path: root/utils/makehrtf.c

/*
 * HRTF utility for producing and demonstrating the process of creating an
 * OpenAL Soft compatible HRIR data set.
 *
 * Copyright (C) 2011-2012  Christopher Fitzgerald
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Or visit:  http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
 *
 * --------------------------------------------------------------------------
 *
 * A big thanks goes out to all those whose work done in the field of
 * binaural sound synthesis using measured HRTFs makes this utility and the
 * OpenAL Soft implementation possible.
 *
 * The algorithm for diffuse-field equalization was adapted from the work
 * done by Rio Emmanuel and Larcher Veronique of IRCAM and Bill Gardner of
 * MIT Media Laboratory.  It operates as follows:
 *
 *  1.  Take the FFT of each HRIR and only keep the magnitude responses.
 *  2.  Calculate the diffuse-field power-average of all HRIRs weighted by
 *      their contribution to the total surface area covered by their
 *      measurement.
 *  3.  Take the diffuse-field average and limit its magnitude range.
 *  4.  Equalize the responses by using the inverse of the diffuse-field
 *      average.
 *  5.  Reconstruct the minimum-phase responses.
 *  5.  Zero the DC component.
 *  6.  IFFT the result and truncate to the desired-length minimum-phase FIR.
 *
 * The spherical head algorithm for calculating propagation delay was adapted
 * from the paper:
 *
 *  Modeling Interaural Time Difference Assuming a Spherical Head
 *  Joel David Miller
 *  Music 150, Musical Acoustics, Stanford University
 *  December 2, 2001
 *
 */

/* Needed for 64-bit unsigned integer. */
#include "config.h"

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <ctype.h>
#include <math.h>

// Rely (if naively) on OpenAL's header for the types used for serialization.
#include "AL/al.h"

#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif

#ifndef HUGE_VAL
#define HUGE_VAL (1.0/0.0)
#endif

// The epsilon used to maintain signal stability.
#define EPSILON                      (1e-15)

// Constants for accessing the token reader's ring buffer.
#define TR_RING_BITS                 (16)
#define TR_RING_SIZE                 (1 << TR_RING_BITS)
#define TR_RING_MASK                 (TR_RING_SIZE - 1)

// The token reader's load interval in bytes.
#define TR_LOAD_SIZE                 (TR_RING_SIZE >> 2)

// The maximum identifier length used when processing the data set
// definition.
#define MAX_IDENT_LEN                (16)

// The maximum path length used when processing filenames.
#define MAX_PATH_LEN                 (256)

// The limits for the sample 'rate' metric in the data set definition.
#define MIN_RATE                     (32000)
#define MAX_RATE                     (96000)

// The limits for the HRIR 'points' metric in the data set definition.
#define MIN_POINTS                   (16)
#define MAX_POINTS                   (8192)

// The limits to the number of 'azimuths' listed in the data set definition.
#define MIN_EV_COUNT                 (5)
#define MAX_EV_COUNT                 (128)

// The limits for each of the 'azimuths' listed in the data set definition.
#define MIN_AZ_COUNT                 (1)
#define MAX_AZ_COUNT                 (128)

// The limits for the listener's head 'radius' in the data set definition.
#define MIN_RADIUS                   (0.05)
#define MAX_RADIUS                   (0.15)

// The limits for the 'distance' from source to listener in the definition
// file.
#define MIN_DISTANCE                 (0.5)
#define MAX_DISTANCE                 (2.5)

// The maximum number of channels that can be addressed for a WAVE file
// source listed in the data set definition.
#define MAX_WAVE_CHANNELS            (65535)

// The limits to the byte size for a binary source listed in the definition
// file.
#define MIN_BIN_SIZE                 (2)
#define MAX_BIN_SIZE                 (4)

// The minimum number of significant bits for binary sources listed in the
// data set definition.  The maximum is calculated from the byte size.
#define MIN_BIN_BITS                 (16)

// The limits to the number of significant bits for an ASCII source listed in
// the data set definition.
#define MIN_ASCII_BITS               (16)
#define MAX_ASCII_BITS               (32)

// The limits to the FFT window size override on the command line.
#define MIN_FFTSIZE                  (512)
#define MAX_FFTSIZE                  (16384)

// The limits to the equalization range limit on the command line.
#define MIN_LIMIT                    (2.0)
#define MAX_LIMIT                    (120.0)

// The limits to the truncation window size on the command line.
#define MIN_TRUNCSIZE                (8)
#define MAX_TRUNCSIZE                (128)

// The truncation window size must be a multiple of the below value to allow
// for vectorized convolution.
#define MOD_TRUNCSIZE                (8)

// The defaults for the command line options.
#define DEFAULT_EQUALIZE             (1)
#define DEFAULT_SURFACE              (1)
#define DEFAULT_LIMIT                (24.0)
#define DEFAULT_TRUNCSIZE            (32)

// The four-character-codes for RIFF/RIFX WAVE file chunks.
#define FOURCC_RIFF                  (0x46464952) // 'RIFF'
#define FOURCC_RIFX                  (0x58464952) // 'RIFX'
#define FOURCC_WAVE                  (0x45564157) // 'WAVE'
#define FOURCC_FMT                   (0x20746D66) // 'fmt '
#define FOURCC_DATA                  (0x61746164) // 'data'
#define FOURCC_LIST                  (0x5453494C) // 'LIST'
#define FOURCC_WAVL                  (0x6C766177) // 'wavl'
#define FOURCC_SLNT                  (0x746E6C73) // 'slnt'

// The supported wave formats.
#define WAVE_FORMAT_PCM              (0x0001)
#define WAVE_FORMAT_IEEE_FLOAT       (0x0003)
#define WAVE_FORMAT_EXTENSIBLE       (0xFFFE)

// The maximum propagation delay value supported by OpenAL Soft.
#define MAX_HRTD                     (63.0)

// The OpenAL Soft HRTF format marker.  It stands for minimum-phase head
// response protocol 01.
#define MHR_FORMAT                   ("MinPHR01")

// Byte order for the serialization routines.
enum ByteOrderT {
  BO_NONE   = 0,
  BO_LITTLE    ,
  BO_BIG
};

// Source format for the references listed in the data set definition.
enum SourceFormatT {
  SF_NONE   = 0,
  SF_WAVE      ,  // RIFF/RIFX WAVE file.
  SF_BIN_LE    ,  // Little-endian binary file.
  SF_BIN_BE    ,  // Big-endian binary file.
  SF_ASCII        // ASCII text file.
};

// Element types for the references listed in the data set definition.
enum ElementTypeT {
  ET_NONE = 0,
  ET_INT     ,    // Integer elements.
  ET_FP           // Floating-point elements.
};

// Desired output format from the command line.
enum OutputFormatT {
  OF_NONE  = 0,
  OF_MHR      ,   // OpenAL Soft MHR data set file.
  OF_TABLE        // OpenAL Soft built-in table file (used when compiling).
};

// Unsigned integer type.
typedef unsigned int                 uint;

// Serialization types.  The trailing digit indicates the number of bytes.
typedef ALubyte                      uint1;

typedef ALint                        int4;
typedef ALuint                       uint4;

#if defined (HAVE_STDINT_H)
#include <stdint.h>

typedef uint64_t                     uint8;
#elif defined (HAVE___INT64)
typedef unsigned __int64             uint8;
#elif (SIZEOF_LONG == 8)
typedef unsigned long                uint8;
#elif (SIZEOF_LONG_LONG == 8)
typedef unsigned long long           uint8;
#endif

typedef enum ByteOrderT              ByteOrderT;
typedef enum SourceFormatT           SourceFormatT;
typedef enum ElementTypeT            ElementTypeT;
typedef enum OutputFormatT           OutputFormatT;

typedef struct TokenReaderT          TokenReaderT;
typedef struct SourceRefT            SourceRefT;
typedef struct HrirDataT             HrirDataT;

// Token reader state for parsing the data set definition.
struct TokenReaderT {
  FILE                             * mFile;
  const char                       * mName;
  uint                               mLine,
                                     mColumn;
  char                               mRing [TR_RING_SIZE];
  size_t                             mIn,
                                     mOut;
};

// Source reference state used when loading sources.
struct SourceRefT {
  SourceFormatT                      mFormat;
  ElementTypeT                       mType;
  uint                               mSize;
  int                                mBits;
  uint                               mChannel,
                                     mSkip,
                                     mOffset;
  char                               mPath [MAX_PATH_LEN + 1];
};

// The HRIR metrics and data set used when loading, processing, and storing
// the resulting HRTF.
struct HrirDataT {
  uint                               mIrRate,
                                     mIrCount;
  size_t                             mIrSize,
                                     mIrPoints,
                                     mFftSize;
  uint                               mEvCount,
                                     mEvStart,
                                     mAzCount [MAX_EV_COUNT],
                                     mEvOffset [MAX_EV_COUNT];
  double                             mRadius,
                                     mDistance,
                                   * mHrirs,
                                   * mHrtds,
                                     mMaxHrtd;
};

/* Token reader routines for parsing text files.  Whitespace is not
 * significant.  It can process tokens as identifiers, numbers (integer and
 * floating-point), strings, and operators.  Strings must be encapsulated by
 * double-quotes and cannot span multiple lines.
 */

// Setup the reader on the given file.  The filename can be NULL if no error
// output is desired.
static void TrSetup (FILE * fp, const char * filename, TokenReaderT * tr) {
  const char * name = NULL;
  char ch;

  tr -> mFile = fp;
  name = filename;
  // If a filename was given, store a pointer to the base name.
  if (filename != NULL) {
     while ((ch = (* filename)) != '\0') {
       if ((ch == '/') || (ch == '\\'))
          name = filename + 1;
       filename ++;
     }
  }
  tr -> mName = name;
  tr -> mLine = 1;
  tr -> mColumn = 1;
  tr -> mIn = 0;
  tr -> mOut = 0;
}

// Prime the reader's ring buffer, and return a result indicating that there
// is text to process.
static int TrLoad (TokenReaderT * tr) {
  size_t toLoad, in, count;

  toLoad = TR_RING_SIZE - (tr -> mIn - tr -> mOut);
  if ((toLoad >= TR_LOAD_SIZE) && (! feof (tr -> mFile))) {
     // Load TR_LOAD_SIZE (or less if at the end of the file) per read.
     toLoad = TR_LOAD_SIZE;
     in = tr -> mIn & TR_RING_MASK;
     count = TR_RING_SIZE - in;
     if (count < toLoad) {
        tr -> mIn += fread (& tr -> mRing [in], 1, count, tr -> mFile);
        tr -> mIn += fread (& tr -> mRing [0], 1, toLoad - count, tr -> mFile);
     } else {
        tr -> mIn += fread (& tr -> mRing [in], 1, toLoad, tr -> mFile);
     }
     if (tr -> mOut >= TR_RING_SIZE) {
        tr -> mOut -= TR_RING_SIZE;
        tr -> mIn -= TR_RING_SIZE;
     }
  }
  if (tr -> mIn > tr -> mOut)
     return (1);
  return (0);
}

// Error display routine.  Only displays when the base name is not NULL.
static void TrErrorVA (const TokenReaderT * tr, uint line, uint column, const char * format, va_list argPtr) {
  if (tr -> mName != NULL) {
     fprintf (stderr, "Error (%s:%d:%d):  ", tr -> mName, line, column);
     vfprintf (stderr, format, argPtr);
  }
}

// Used to display an error at a saved line/column.
static void TrErrorAt (const TokenReaderT * tr, uint line, uint column, const char * format, ...) {
  va_list argPtr;

  va_start (argPtr, format);
  TrErrorVA (tr, line, column, format, argPtr);
  va_end (argPtr);
}

// Used to display an error at the current line/column.
static void TrError (const TokenReaderT * tr, const char * format, ...) {
  va_list argPtr;

  va_start (argPtr, format);
  TrErrorVA (tr, tr -> mLine, tr -> mColumn, format, argPtr);
  va_end (argPtr);
}

// Skips to the next line.
static void TrSkipLine (TokenReaderT * tr) {
  char ch;

  while (TrLoad (tr)) {
    ch = tr -> mRing [tr -> mOut & TR_RING_MASK];
    tr -> mOut ++;
    if (ch == '\n') {
       tr -> mLine ++;
       tr -> mColumn = 1;
       break;
    }
    tr -> mColumn ++;
  }
}

// Skips to the next token.
static int TrSkipWhitespace (TokenReaderT * tr) {
  char ch;

  while (TrLoad (tr)) {
    ch = tr -> mRing [tr -> mOut & TR_RING_MASK];
    if (isspace (ch)) {
       tr -> mOut ++;
       if (ch == '\n') {
          tr -> mLine ++;
          tr -> mColumn = 1;
       } else {
          tr -> mColumn ++;
       }
    } else if (ch == '#') {
       TrSkipLine (tr);
    } else {
       return (1);
    }
  }
  return (0);
}

// Get the line and/or column of the next token (or the end of input).
static void TrIndication (TokenReaderT * tr, uint * line, uint * column) {
  TrSkipWhitespace (tr);
  if (line != NULL)
     (* line) = tr -> mLine;
  if (column != NULL)
     (* column) = tr -> mColumn;
}

// Checks to see if a token is the given operator.  It does not display any
// errors and will not proceed to the next token.
static int TrIsOperator (TokenReaderT * tr, const char * op) {
  size_t out, len;
  char ch;

  if (! TrSkipWhitespace (tr))
     return (0);
  out = tr -> mOut;
  len = 0;
  while ((op [len] != '\0') && (out < tr -> mIn)) {
    ch = tr -> mRing [out & TR_RING_MASK];
    if (ch != op [len])
       break;
    len ++;
    out ++;
  }
  if (op [len] == '\0')
     return (1);
  return (0);
}

/* The TrRead*() routines obtain the value of a matching token type.  They
 * display type, form, and boundary errors and will proceed to the next
 * token.
 */

// Reads and validates an identifier token.
static int TrReadIdent (TokenReaderT * tr, const size_t maxLen, char * ident) {
  uint col;
  size_t len;
  char ch;

  col = tr -> mColumn;
  if (TrSkipWhitespace (tr)) {
     col = tr -> mColumn;
     ch = tr -> mRing [tr -> mOut & TR_RING_MASK];
     if ((ch == '_') || isalpha (ch)) {
        len = 0;
        do {
          if (len < maxLen)
             ident [len] = ch;
          len ++;
          tr -> mOut ++;
          if (! TrLoad (tr))
             break;
          ch = tr -> mRing [tr -> mOut & TR_RING_MASK];
        } while ((ch == '_') || isdigit (ch) || isalpha (ch));
        tr -> mColumn += len;
        if (len > maxLen) {
           TrErrorAt (tr, tr -> mLine, col, "Identifier is too long.\n");
           return (0);
        }
        ident [len] = '\0';
        return (1);
     }
  }
  TrErrorAt (tr, tr -> mLine, col, "Expected an identifier.\n");
  return (0);
}

// Reads and validates (including bounds) an integer token.
static int TrReadInt (TokenReaderT * tr, const int loBound, const int hiBound, int * value) {
  uint col, digis;
  size_t len;
  char ch, temp [64 + 1];

  col = tr -> mColumn;
  if (TrSkipWhitespace (tr)) {
     col = tr -> mColumn;
     len = 0;
     ch = tr -> mRing [tr -> mOut & TR_RING_MASK];
     if ((ch == '+') || (ch == '-')) {
        temp [len] = ch;
        len ++;
        tr -> mOut ++;
     }
     digis = 0;
     while (TrLoad (tr)) {
       ch = tr -> mRing [tr -> mOut & TR_RING_MASK];
       if (! isdigit (ch))
          break;
       if (len < 64)
          temp [len] = ch;
       len ++;
       digis ++;
       tr -> mOut ++;
     }
     tr -> mColumn += len;
     if ((digis > 0) && (ch != '.') && (! isalpha (ch))) {
        if (len > 64) {
           TrErrorAt (tr, tr -> mLine, col, "Integer is too long.");
           return (0);
        }
        temp [len] = '\0';
        (* value) = strtol (temp, NULL, 10);
        if (((* value) < loBound) || ((* value) > hiBound)) {
           TrErrorAt (tr, tr -> mLine, col, "Expected a value from %d to %d.\n", loBound, hiBound);
           return (0);
        }
        return (1);
     }
  }
  TrErrorAt (tr, tr -> mLine, col, "Expected an integer.\n");
  return (0);
}

// Reads and validates (including bounds) a float token.
static int TrReadFloat (TokenReaderT * tr, const double loBound, const double hiBound, double * value) {
  uint col, digis;
  size_t len;
  char ch, temp [64 + 1];

  col = tr -> mColumn;
  if (TrSkipWhitespace (tr)) {
     col = tr -> mColumn;
     len = 0;
     ch = tr -> mRing [tr -> mOut & TR_RING_MASK];
     if ((ch == '+') || (ch == '-')) {
        temp [len] = ch;
        len ++;
        tr -> mOut ++;
     }
     digis = 0;
     while (TrLoad (tr)) {
       ch = tr -> mRing [tr -> mOut & TR_RING_MASK];
       if (! isdigit (ch))
          break;
       if (len < 64)
          temp [len] = ch;
       len ++;
       digis ++;
       tr -> mOut ++;
     }
     if (ch == '.') {
        if (len < 64)
           temp [len] = ch;
        len ++;
        tr -> mOut ++;
     }
     while (TrLoad (tr)) {
       ch = tr -> mRing [tr -> mOut & TR_RING_MASK];
       if (! isdigit (ch))
          break;
       if (len < 64)
          temp [len] = ch;
       len ++;
       digis ++;
       tr -> mOut ++;
     }
     if (digis > 0) {
        if ((ch == 'E') || (ch == 'e')) {
           if (len < 64)
              temp [len] = ch;
           len ++;
           digis = 0;
           tr -> mOut ++;
           if ((ch == '+') || (ch == '-')) {
              if (len < 64)
                 temp [len] = ch;
              len ++;
              tr -> mOut ++;
           }
           while (TrLoad (tr)) {
             ch = tr -> mRing [tr -> mOut & TR_RING_MASK];
             if (! isdigit (ch))
                break;
             if (len < 64)
                temp [len] = ch;
             len ++;
             digis ++;
             tr -> mOut ++;
           }
        }
        tr -> mColumn += len;
        if ((digis > 0) && (ch != '.') && (! isalpha (ch))) {
           if (len > 64) {
              TrErrorAt (tr, tr -> mLine, col, "Float is too long.");
              return (0);
           }
           temp [len] = '\0';
           (* value) = strtod (temp, NULL);
           if (((* value) < loBound) || ((* value) > hiBound)) {
              TrErrorAt (tr, tr -> mLine, col, "Expected a value from %f to %f.\n", loBound, hiBound);
              return (0);
           }
           return (1);
        }
     } else {
        tr -> mColumn += len;
     }
  }
  TrErrorAt (tr, tr -> mLine, col, "Expected a float.\n");
  return (0);
}

// Reads and validates a string token.
static int TrReadString (TokenReaderT * tr, const size_t maxLen, char * text) {
  uint col;
  size_t len;
  char ch;

  col = tr -> mColumn;
  if (TrSkipWhitespace (tr)) {
     col = tr -> mColumn;
     ch = tr -> mRing [tr -> mOut & TR_RING_MASK];
     if (ch == '\"') {
        tr -> mOut ++;
        len = 0;
        while (TrLoad (tr)) {
          ch = tr -> mRing [tr -> mOut & TR_RING_MASK];
          tr -> mOut ++;
          if (ch == '\"')
             break;
          if (ch == '\n') {
             TrErrorAt (tr, tr -> mLine, col, "Unterminated string at end of line.\n");
             return (0);
          }
          if (len < maxLen)
             text [len] = ch;
          len ++;
        }
        if (ch != '\"') {
           tr -> mColumn += 1 + len;
           TrErrorAt (tr, tr -> mLine, col, "Unterminated string at end of input.\n");
           return (0);
        }
        tr -> mColumn += 2 + len;
        if (len > maxLen) {
           TrErrorAt (tr, tr -> mLine, col, "String is too long.\n");
           return (0);
        }
        text [len] = '\0';
        return (1);
     }
  }
  TrErrorAt (tr, tr -> mLine, col, "Expected a string.\n");
  return (0);
}

// Reads and validates the given operator.
static int TrReadOperator (TokenReaderT * tr, const char * op) {
  uint col;
  size_t len;
  char ch;

  col = tr -> mColumn;
  if (TrSkipWhitespace (tr)) {
     col = tr -> mColumn;
     len = 0;
     while ((op [len] != '\0') && TrLoad (tr)) {
       ch = tr -> mRing [tr -> mOut & TR_RING_MASK];
       if (ch != op [len])
          break;
       len ++;
       tr -> mOut ++;
     }
     tr -> mColumn += len;
     if (op [len] == '\0')
        return (1);
  }
  TrErrorAt (tr, tr -> mLine, col, "Expected '%s' operator.\n", op);
  return (0);
}

/* Performs a string substitution.  Any case-insensitive occurrences of the
 * pattern string are replaced with the replacement string.  The result is
 * truncated if necessary.
 */
static int StrSubst (const char * in, const char * pat, const char * rep, const size_t maxLen, char * out) {
  size_t inLen, patLen, repLen;
  size_t si, di;
  int truncated;

  inLen = strlen (in);
  patLen = strlen (pat);
  repLen = strlen (rep);
  si = 0;
  di = 0;
  truncated = 0;
  while ((si < inLen) && (di < maxLen)) {
    if (patLen <= (inLen - si)) {
       if (strncasecmp (& in [si], pat, patLen) == 0) {
          if (repLen > (maxLen - di)) {
             repLen = maxLen - di;
             truncated = 1;
          }
          strncpy (& out [di], rep, repLen);
          si += patLen;
          di += repLen;
       }
    }
    out [di] = in [si];
    si ++;
    di ++;
  }
  if (si < inLen)
     truncated = 1;
  out [di] = '\0';
  return (! truncated);
}

// Provide missing math routines for MSVC.
#ifdef _MSC_VER
static double round (double val) {
  if (val < 0.0)
     return (ceil (val - 0.5));
  return (floor (val + 0.5));
}

static double fmin (double a, double b) {
  return ((a < b) ? a : b);
}

static double fmax (double a, double b) {
  return ((a > b) ? a : b);
}
#endif

// Simple clamp routine.
static double Clamp (const double val, const double lower, const double upper) {
  return (fmin (fmax (val, lower), upper));
}

// Performs linear interpolation.
static double Lerp (const double a, const double b, const double f) {
  return (a + (f * (b - a)));
}

// Performs a high-passed triangular probability density function dither from
// a double to an integer.  It assumes the input sample is already scaled.
static int HpTpdfDither (const double in, int * hpHist) {
  const double PRNG_SCALE = 1.0 / RAND_MAX;
  int prn;
  double out;

  prn = rand ();
  out = round (in + (PRNG_SCALE * (prn - (* hpHist))));
  (* hpHist) = prn;
  return ((int) out);
}

// Allocates an array of doubles.
static double * CreateArray (const size_t n) {
  double * a = NULL;

  a = (double *) calloc (n, sizeof (double));
  if (a == NULL) {
     fprintf (stderr, "Error:  Out of memory.\n");
     exit (-1);
  }
  return (a);
}

// Frees an array of doubles.
static void DestroyArray (const double * a) {
  free ((void *) a);
}

// Complex number routines.  All outputs must be non-NULL.

// Magnitude/absolute value.
static double ComplexAbs (const double r, const double i) {
  return (sqrt ((r * r) + (i * i)));
}

// Multiply.
static void ComplexMul (const double aR, const double aI, const double bR, const double bI, double * outR, double * outI) {
  (* outR) = (aR * bR) - (aI * bI);
  (* outI) = (aI * bR) + (aR * bI);
}

// Base-e exponent.
static void ComplexExp (const double inR, const double inI, double * outR, double * outI) {
  double e;

  e = exp (inR);
  (* outR) = e * cos (inI);
  (* outI) = e * sin (inI);
}

/* Fast Fourier transform routines.  The number of points must be a power of
 * two.  In-place operation is possible only if both the real and imaginary
 * parts are in-place together.
 */

// Performs bit-reversal ordering.
static void FftArrange (const size_t n, const double * inR, const double * inI, double * outR, double * outI) {
  size_t rk, k, m;
  double tempR, tempI;

  if ((inR == outR) && (inI == outI)) {
     // Handle in-place arrangement.
     rk = 0;
     for (k = 0; k < n; k ++) {
         if (rk > k) {
            tempR = inR [rk];
            tempI = inI [rk];
            outR [rk] = inR [k];
            outI [rk] = inI [k];
            outR [k] = tempR;
            outI [k] = tempI;
         }
         m = n;
         while (rk & (m >>= 1))
           rk &= ~m;
         rk |= m;
     }
  } else {
     // Handle copy arrangement.
     rk = 0;
     for (k = 0; k < n; k ++) {
         outR [rk] = inR [k];
         outI [rk] = inI [k];
         m = n;
         while (rk & (m >>= 1))
           rk &= ~m;
         rk |= m;
     }
  }
}

// Performs the summation.
static void FftSummation (const size_t n, const double s, double * re, double * im) {
  double pi;
  size_t m, m2;
  double vR, vI, wR, wI;
  size_t i, k, mk;
  double tR, tI;

  pi = s * M_PI;
  for (m = 1, m2 = 2; m < n; m <<= 1, m2 <<= 1) {
      // v = Complex (-2.0 * sin (0.5 * pi / m) * sin (0.5 * pi / m), -sin (pi / m))
      vR = sin (0.5 * pi / m);
      vR = -2.0 * vR * vR;
      vI = -sin (pi / m);
      // w = Complex (1.0, 0.0)
      wR = 1.0;
      wI = 0.0;
      for (i = 0; i < m; i ++) {
          for (k = i; k < n; k += m2) {
              mk = k + m;
              // t = ComplexMul (w, out [km2])
              tR = (wR * re [mk]) - (wI * im [mk]);
              tI = (wR * im [mk]) + (wI * re [mk]);
              // out [mk] = ComplexSub (out [k], t)
              re [mk] = re [k] - tR;
              im [mk] = im [k] - tI;
              // out [k] = ComplexAdd (out [k], t)
              re [k] += tR;
              im [k] += tI;
          }
          // t = ComplexMul (v, w)
          tR = (vR * wR) - (vI * wI);
          tI = (vR * wI) + (vI * wR);
          // w = ComplexAdd (w, t)
          wR += tR;
          wI += tI;
      }
  }
}

// Performs a forward FFT.
static void FftForward (const size_t n, const double * inR, const double * inI, double * outR, double * outI) {
  FftArrange (n, inR, inI, outR, outI);
  FftSummation (n, 1.0, outR, outI);
}

// Performs an inverse FFT.
static void FftInverse (const size_t n, const double * inR, const double * inI, double * outR, double * outI) {
  double f;
  size_t i;

  FftArrange (n, inR, inI, outR, outI);
  FftSummation (n, -1.0, outR, outI);
  f = 1.0 / n;
  for (i = 0; i < n; i ++) {
      outR [i] *= f;
      outI [i] *= f;
  }
}

/* Calculate the complex helical sequence (or discrete-time analytical
 * signal) of the given input using the Hilbert transform.  Given the
 * negative natural logarithm of a signal's magnitude response, the imaginary
 * components can be used as the angles for minimum-phase reconstruction.
 */
static void Hilbert (const size_t n, const double * in, double * outR, double * outI) {
  size_t i;

  if (in == outR) {
     // Handle in-place operation.
     for (i = 0; i < n; i ++)
         outI [i] = 0.0;
  } else {
     // Handle copy operation.
     for (i = 0; i < n; i ++) {
         outR [i] = in [i];
         outI [i] = 0.0;
     }
  }
  FftForward (n, outR, outI, outR, outI);
  /* Currently the Fourier routines operate only on point counts that are
   * powers of two.  If that changes and n is odd, the following conditional
   * should be:  i < (n + 1) / 2.
   */
  for (i = 1; i < (n / 2); i ++) {
      outR [i] *= 2.0;
      outI [i] *= 2.0;
  }
  // If n is odd, the following increment should be skipped.
  i ++;
  for (; i < n; i ++) {
      outR [i] = 0.0;
      outI [i] = 0.0;
  }
  FftInverse (n, outR, outI, outR, outI);
}

/* Calculate the magnitude response of the given input.  This is used in
 * place of phase decomposition, since the phase residuals are discarded for
 * minimum phase reconstruction.  The mirrored half of the response is also
 * discarded.
 */
static void MagnitudeResponse (const size_t n, const double * inR, const double * inI, double * out) {
  const size_t m = 1 + (n / 2);
  size_t i;

  for (i = 0; i < m; i ++)
      out [i] = fmax (ComplexAbs (inR [i], inI [i]), EPSILON);
}

/* Apply a range limit (in dB) to the given magnitude response.  This is used
 * to adjust the effects of the diffuse-field average on the equalization
 * process.
 */
static void LimitMagnitudeResponse (const size_t n, const double limit, const double * in, double * out) {
  const size_t m = 1 + (n / 2);
  double halfLim;
  size_t i, lower, upper;
  double ave;

  halfLim = limit / 2.0;
  // Convert the response to dB.
  for (i = 0; i < m; i ++)
      out [i] = 20.0 * log10 (in [i]);
  // Use six octaves to calculate the average magnitude of the signal.
  lower = ((size_t) ceil (n / pow (2.0, 8.0))) - 1;
  upper = ((size_t) floor (n / pow (2.0, 2.0))) - 1;
  ave = 0.0;
  for (i = lower; i <= upper; i ++)
      ave += out [i];
  ave /= upper - lower + 1;
  // Keep the response within range of the average magnitude.
  for (i = 0; i < m; i ++)
      out [i] = Clamp (out [i], ave - halfLim, ave + halfLim);
  // Convert the response back to linear magnitude.
  for (i = 0; i < m; i ++)
      out [i] = pow (10.0, out [i] / 20.0);
}

/* Reconstructs the minimum-phase component for the given magnitude response
 * of a signal.  This is equivalent to phase recomposition, sans the missing
 * residuals (which were discarded).  The mirrored half of the response is
 * reconstructed.
 */
static void MinimumPhase (const size_t n, const double * in, double * outR, double * outI) {
  const size_t m = 1 + (n / 2);
  double * mags = NULL;
  size_t i;
  double aR, aI;

  mags = CreateArray (n);
  for (i = 0; i < m; i ++) {
      mags [i] = fmax (in [i], EPSILON);
      outR [i] = -log (mags [i]);
  }
  for (; i < n; i ++) {
      mags [i] = mags [n - i];
      outR [i] = outR [n - i];
  }
  Hilbert (n, outR, outR, outI);
  // Remove any DC offset the filter has.
  outR [0] = 0.0;
  outI [0] = 0.0;
  for (i = 1; i < n; i ++) {
      ComplexExp (0.0, outI [i], & aR, & aI);
      ComplexMul (mags [i], 0.0, aR, aI, & outR [i], & outI [i]);
  }
  DestroyArray (mags);
}

// Read a binary value of the specified byte order and byte size from a file,
// storing it as a 32-bit unsigned integer.
static int ReadBin4 (FILE * fp, const char * filename, const ByteOrderT order, const uint bytes, uint4 * out) {
  uint1 in [4];
  uint4 accum;
  uint i;

  if (fread (in, 1, bytes, fp) != bytes) {
     fprintf (stderr, "Error:  Bad read from file '%s'.\n", filename);
     return (0);
  }
  accum = 0;
  switch (order) {
    case BO_LITTLE :
      for (i = 0; i < bytes; i ++)
          accum = (accum << 8) | in [bytes - i - 1];
    break;
    case BO_BIG :
      for (i = 0; i < bytes; i ++)
          accum = (accum << 8) | in [i];
    break;
    default :
    break;
  }
  (* out) = accum;
  return (1);
}

// Read a binary value of the specified byte order from a file, storing it as
// a 64-bit unsigned integer.
static int ReadBin8 (FILE * fp, const char * filename, const ByteOrderT order, uint8 * out) {
  uint1 in [8];
  uint8 accum;
  uint i;

  if (fread (in, 1, 8, fp) != 8) {
     fprintf (stderr, "Error:  Bad read from file '%s'.\n", filename);
     return (0);
  }
  accum = 0ULL;
  switch (order) {
    case BO_LITTLE :
      for (i = 0; i < 8; i ++)
          accum = (accum << 8) | in [8 - i - 1];
    break;
    case BO_BIG :
      for (i = 0; i < 8; i ++)
          accum = (accum << 8) | in [i];
    break;
    default :
    break;
  }
  (* out) = accum;
  return (1);
}

// Write an ASCII string to a file.
static int WriteAscii (const char * out, FILE * fp, const char * filename) {
  size_t len;

  len = strlen (out);
  if (fwrite (out, 1, len, fp) != len) {
     fclose (fp);
     fprintf (stderr, "Error:  Bad write to file '%s'.\n", filename);
     return (0);
  }
  return (1);
}

// Write a binary value of the given byte order and byte size to a file,
// loading it from a 32-bit unsigned integer.
static int WriteBin4 (const ByteOrderT order, const uint bytes, const uint4 in, FILE * fp, const char * filename) {
  uint1 out [4];
  uint i;

  switch (order) {
    case BO_LITTLE :
      for (i = 0; i < bytes; i ++)
          out [i] = (in >> (i * 8)) & 0x000000FF;
    break;
    case BO_BIG :
      for (i = 0; i < bytes; i ++)
          out [bytes - i - 1] = (in >> (i * 8)) & 0x000000FF;
    break;
    default :
    break;
  }
  if (fwrite (out, 1, bytes, fp) != bytes) {
     fprintf (stderr, "Error:  Bad write to file '%s'.\n", filename);
     return (0);
  }
  return (1);
}

/* Read a binary value of the specified type, byte order, and byte size from
 * a file, converting it to a double.  For integer types, the significant
 * bits are used to normalize the result.  The sign of bits determines
 * whether they are padded toward the MSB (negative) or LSB (positive).
 * Floating-point types are not normalized.
 */
static int ReadBinAsDouble (FILE * fp, const char * filename, const ByteOrderT order, const ElementTypeT type, const uint bytes, const int bits, double * out) {
  union {
    uint4 ui;
    int4 i;
    float f;
  } v4;
  union {
    uint8 ui;
    double f;
  } v8;

  (* out) = 0.0;
  if (bytes > 4) {
     if (! ReadBin8 (fp, filename, order, & v8 . ui))
        return (0);
     if (type == ET_FP)
        (* out) = v8 . f;
  } else {
     if (! ReadBin4 (fp, filename, order, bytes, & v4 . ui))
        return (0);
     if (type == ET_FP) {
        (* out) = (double) v4 . f;
     } else {
        if (bits > 0)
           v4 . ui >>= (8 * bytes) - bits;
        else
           v4 . ui &= (0xFFFFFFFF >> (32 + bits));
        if (v4 . ui & (1 << (abs (bits) - 1)))
           v4 . ui |= (0xFFFFFFFF << abs (bits));
        (* out) = v4 . i / ((double) (1 << (abs (bits) - 1)));
     }
  }
  return (1);
}

/* Read an ascii value of the specified type from a file, converting it to a
 * double.  For integer types, the significant bits are used to normalize the
 * result.  The sign of the bits should always be positive.  This also skips
 * up to one separator character before the element itself.
 */
static int ReadAsciiAsDouble (TokenReaderT * tr, const char * filename, const ElementTypeT type, const uint bits, double * out) {
  int v;

  if (TrIsOperator (tr, ","))
     TrReadOperator (tr, ",");
  else if (TrIsOperator (tr, ":"))
     TrReadOperator (tr, ":");
  else if (TrIsOperator (tr, ";"))
     TrReadOperator (tr, ";");
  else if (TrIsOperator (tr, "|"))
     TrReadOperator (tr, "|");
  if (type == ET_FP) {
     if (! TrReadFloat (tr, -HUGE_VAL, HUGE_VAL, out)) {
        fprintf (stderr, "Error:  Bad read from file '%s'.\n", filename);
        return (0);
     }
  } else {
     if (! TrReadInt (tr, -(1 << (bits - 1)), (1 << (bits - 1)) - 1, & v)) {
        fprintf (stderr, "Error:  Bad read from file '%s'.\n", filename);
        return (0);
     }
     (* out) = v / ((double) ((1 << (bits - 1)) - 1));
  }
  return (1);
}

// Read the RIFF/RIFX WAVE format chunk from a file, validating it against
// the source parameters and data set metrics.
static int ReadWaveFormat (FILE * fp, const ByteOrderT order, const uint hrirRate, SourceRefT * src) {
  uint4 fourCC, chunkSize;
  uint4 format, channels, rate, dummy, block, size, bits;

  chunkSize = 0;
  do {
    if (chunkSize > 0)
       fseek (fp, chunkSize, SEEK_CUR);
    if ((! ReadBin4 (fp, src -> mPath, BO_LITTLE, 4, & fourCC)) ||
        (! ReadBin4 (fp, src -> mPath, order, 4, & chunkSize)))
       return (0);
  } while (fourCC != FOURCC_FMT);
  if ((! ReadBin4 (fp, src -> mPath, order, 2, & format)) ||
      (! ReadBin4 (fp, src -> mPath, order, 2, & channels)) ||
      (! ReadBin4 (fp, src -> mPath, order, 4, & rate)) ||
      (! ReadBin4 (fp, src -> mPath, order, 4, & dummy)) ||
      (! ReadBin4 (fp, src -> mPath, order, 2, & block)))
     return (0);
  block /= channels;
  if (chunkSize > 14) {
     if (! ReadBin4 (fp, src -> mPath, order, 2, & size))
        return (0);
     size /= 8;
     if (block > size)
        size = block;
  } else {
     size = block;
  }
  if (format == WAVE_FORMAT_EXTENSIBLE) {
     fseek (fp, 2, SEEK_CUR);
     if (! ReadBin4 (fp, src -> mPath, order, 2, & bits))
        return (0);
     if (bits == 0)
        bits = 8 * size;
     fseek (fp, 4, SEEK_CUR);
     if (! ReadBin4 (fp, src -> mPath, order, 2, & format))
        return (0);
     fseek (fp, chunkSize - 26, SEEK_CUR);
  } else {
     bits = 8 * size;
     if (chunkSize > 14)
        fseek (fp, chunkSize - 16, SEEK_CUR);
     else
        fseek (fp, chunkSize - 14, SEEK_CUR);
  }
  if ((format != WAVE_FORMAT_PCM) && (format != WAVE_FORMAT_IEEE_FLOAT)) {
     fprintf (stderr, "Error:  Unsupported WAVE format in file '%s'.\n", src -> mPath);
     return (0);
  }
  if (src -> mChannel >= channels) {
     fprintf (stderr, "Error:  Missing source channel in WAVE file '%s'.\n", src -> mPath);
     return (0);
  }
  if (rate != hrirRate) {
     fprintf (stderr, "Error:  Mismatched source sample rate in WAVE file '%s'.\n", src -> mPath);
     return (0);
  }
  if (format == WAVE_FORMAT_PCM) {
     if ((size < 2) || (size > 4)) {
        fprintf (stderr, "Error:  Unsupported sample size in WAVE file '%s'.\n", src -> mPath);
        return (0);
     }
     if ((bits < 16) || (bits > (8 * size))) {
        fprintf (stderr, "Error:  Bad significant bits in WAVE file '%s'.\n", src -> mPath);
        return (0);
     }
     src -> mType = ET_INT;
  } else {
     if ((size != 4) && (size != 8)) {
        fprintf (stderr, "Error:  Unsupported sample size in WAVE file '%s'.\n", src -> mPath);
        return (0);
     }
     src -> mType = ET_FP;
  }
  src -> mSize = size;
  src -> mBits = (int) bits;
  src -> mSkip = channels;
  return (1);
}

// Read a RIFF/RIFX WAVE data chunk, converting all elements to doubles.
static int ReadWaveData (FILE * fp, const SourceRefT * src, const ByteOrderT order, const size_t n, double * hrir) {
  int pre, post, skip;
  size_t i;

  pre = (int) (src -> mSize * src -> mChannel);
  post = (int) (src -> mSize * (src -> mSkip - src -> mChannel - 1));
  skip = 0;
  for (i = 0; i < n; i ++) {
      skip += pre;
      if (skip > 0)
         fseek (fp, skip, SEEK_CUR);
      if (! ReadBinAsDouble (fp, src -> mPath, order, src -> mType, src -> mSize, src -> mBits, & hrir [i]))
         return (0);
      skip = post;
  }
  if (skip > 0)
     fseek (fp, skip, SEEK_CUR);
  return (1);
}

// Read the RIFF/RIFX WAVE list or data chunk, converting all elements to
// doubles.
static int ReadWaveList (FILE * fp, const SourceRefT * src, const ByteOrderT order, const size_t n, double * hrir) {
  uint4 fourCC, chunkSize, listSize;
  size_t block, skip, count, offset, i;
  double lastSample;

  for (;;) {
      if ((! ReadBin4 (fp, src -> mPath, BO_LITTLE, 4, & fourCC)) ||
          (! ReadBin4 (fp, src -> mPath, order, 4, & chunkSize)))
         return (0);
      if (fourCC == FOURCC_DATA) {
         block = src -> mSize * src -> mSkip;
         count = chunkSize / block;
         if (count < (src -> mOffset + n)) {
            fprintf (stderr, "Error:  Bad read from file '%s'.\n", src -> mPath);
            return (0);
         }
         fseek (fp, src -> mOffset * block, SEEK_CUR);
         if (! ReadWaveData (fp, src, order, n, & hrir [0]))
            return (0);
         return (1);
      } else if (fourCC == FOURCC_LIST) {
         if (! ReadBin4 (fp, src -> mPath, BO_LITTLE, 4, & fourCC))
            return (0);
         chunkSize -= 4;
         if (fourCC == FOURCC_WAVL)
            break;
      }
      if (chunkSize > 0)
         fseek (fp, chunkSize, SEEK_CUR);
  }
  listSize = chunkSize;
  block = src -> mSize * src -> mSkip;
  skip = src -> mOffset;
  offset = 0;
  lastSample = 0.0;
  while ((offset < n) && (listSize > 8)) {
    if ((! ReadBin4 (fp, src -> mPath, BO_LITTLE, 4, & fourCC)) ||
        (! ReadBin4 (fp, src -> mPath, order, 4, & chunkSize)))
       return (0);
    listSize -= 8 + chunkSize;
    if (fourCC == FOURCC_DATA) {
       count = chunkSize / block;
       if (count > skip) {
          fseek (fp, skip * block, SEEK_CUR);
          chunkSize -= skip * block;
          count -= skip;
          skip = 0;
          if (count > (n - offset))
             count = n - offset;
          if (! ReadWaveData (fp, src, order, count, & hrir [offset]))
             return (0);
          chunkSize -= count * block;
          offset += count;
          lastSample = hrir [offset - 1];
       } else {
          skip -= count;
          count = 0;
       }
    } else if (fourCC == FOURCC_SLNT) {
       if (! ReadBin4 (fp, src -> mPath, order, 4, & count))
          return (0);
       chunkSize -= 4;
       if (count > skip) {
          count -= skip;
          skip = 0;
          if (count > (n - offset))
             count = n - offset;
          for (i = 0; i < count; i ++)
              hrir [offset + i] = lastSample;
          offset += count;
       } else {
          skip -= count;
          count = 0;
       }
    }
    if (chunkSize > 0)
       fseek (fp, chunkSize, SEEK_CUR);
  }
  if (offset < n) {
     fprintf (stderr, "Error:  Bad read from file '%s'.\n", src -> mPath);
     return (0);
  }
  return (1);
}

// Load a source HRIR from a RIFF/RIFX WAVE file.
static int LoadWaveSource (FILE * fp, SourceRefT * src, const uint hrirRate, const size_t n, double * hrir) {
  uint4 fourCC, dummy;
  ByteOrderT order;

  if ((! ReadBin4 (fp, src -> mPath, BO_LITTLE, 4, & fourCC)) ||
      (! ReadBin4 (fp, src -> mPath, BO_LITTLE, 4, & dummy)))
     return (0);
  if (fourCC == FOURCC_RIFF) {
     order = BO_LITTLE;
  } else if (fourCC == FOURCC_RIFX) {
     order = BO_BIG;
  } else {
     fprintf (stderr, "Error:  No RIFF/RIFX chunk in file '%s'.\n", src -> mPath);
     return (0);
  }
  if (! ReadBin4 (fp, src -> mPath, BO_LITTLE, 4, & fourCC))
     return (0);
  if (fourCC != FOURCC_WAVE) {
     fprintf (stderr, "Error:  Not a RIFF/RIFX WAVE file '%s'.\n", src -> mPath);
     return (0);
  }
  if (! ReadWaveFormat (fp, order, hrirRate, src))
     return (0);
  if (! ReadWaveList (fp, src, order, n, hrir))
     return (0);
  return (1);
}

// Load a source HRIR from a binary file.
static int LoadBinarySource (FILE * fp, const SourceRefT * src, const ByteOrderT order, const size_t n, double * hrir) {
  size_t i;

  fseek (fp, src -> mOffset, SEEK_SET);
  for (i = 0; i < n; i ++) {
      if (! ReadBinAsDouble (fp, src -> mPath, order, src -> mType, src -> mSize, src -> mBits, & hrir [i]))
         return (0);
      if (src -> mSkip > 0)
         fseek (fp, src -> mSkip, SEEK_CUR);
  }
  return (1);
}

// Load a source HRIR from an ASCII text file containing a list of elements
// separated by whitespace or common list operators (',', ';', ':', '|').
static int LoadAsciiSource (FILE * fp, const SourceRefT * src, const size_t n, double * hrir) {
  TokenReaderT tr;
  size_t i, j;
  double dummy;

  TrSetup (fp, NULL, & tr);
  for (i = 0; i < src -> mOffset; i ++) {
      if (! ReadAsciiAsDouble (& tr, src -> mPath, src -> mType, src -> mBits, & dummy))
         return (0);
  }
  for (i = 0; i < n; i ++) {
      if (! ReadAsciiAsDouble (& tr, src -> mPath, src -> mType, src -> mBits, & hrir [i]))
         return (0);
      for (j = 0; j < src -> mSkip; j ++) {
          if (! ReadAsciiAsDouble (& tr, src -> mPath, src -> mType, src -> mBits, & dummy))
             return (0);
      }
  }
  return (1);
}

// Load a source HRIR from a supported file type.
static int LoadSource (SourceRefT * src, const uint hrirRate, const size_t n, double * hrir) {
  FILE * fp = NULL;
  int result;

  if (src -> mFormat == SF_ASCII)
     fp = fopen (src -> mPath, "r");
  else
     fp = fopen (src -> mPath, "rb");
  if (fp == NULL) {
     fprintf (stderr, "Error:  Could not open source file '%s'.\n", src -> mPath);
     return (0);
  }
  if (src -> mFormat == SF_WAVE)
     result = LoadWaveSource (fp, src, hrirRate, n, hrir);
  else if (src -> mFormat == SF_BIN_LE)
     result = LoadBinarySource (fp, src, BO_LITTLE, n, hrir);
  else if (src -> mFormat == SF_BIN_BE)
     result = LoadBinarySource (fp, src, BO_BIG, n, hrir);
  else
     result = LoadAsciiSource (fp, src, n, hrir);
  fclose (fp);
  return (result);
}

// Calculate the magnitude response of an HRIR and average it with any
// existing responses for its elevation and azimuth.
static void AverageHrirMagnitude (const double * hrir, const double f, const uint ei, const uint ai, const HrirDataT * hData) {
  double * re = NULL, * im = NULL;
  size_t n, m, i, j;

  n = hData -> mFftSize;
  re = CreateArray (n);
  im = CreateArray (n);
  for (i = 0; i < hData -> mIrPoints; i ++) {
      re [i] = hrir [i];
      im [i] = 0.0;
  }
  for (; i < n; i ++) {
      re [i] = 0.0;
      im [i] = 0.0;
  }
  FftForward (n, re, im, re, im);
  MagnitudeResponse (n, re, im, re);
  m = 1 + (n / 2);
  j = (hData -> mEvOffset [ei] + ai) * hData -> mIrSize;
  for (i = 0; i < m; i ++)
      hData -> mHrirs [j + i] = Lerp (hData -> mHrirs [j + i], re [i], f);
  DestroyArray (im);
  DestroyArray (re);
}

/* Calculate the contribution of each HRIR to the diffuse-field average based
 * on the area of its surface patch.  All patches are centered at the HRIR
 * coordinates on the unit sphere and are measured by solid angle.
 */
static void CalculateDfWeights (const HrirDataT * hData, double * weights) {
  uint ei;
  double evs, sum, ev, up_ev, down_ev, solidAngle;

  evs = 90.0 / (hData -> mEvCount - 1);
  sum = 0.0;
  for (ei = hData -> mEvStart; ei < hData -> mEvCount; ei ++) {
      // For each elevation, calculate the upper and lower limits of the
      // patch band.
      ev = -90.0 + (ei * 2.0 * evs);
      if (ei < (hData -> mEvCount - 1))
         up_ev = (ev + evs) * M_PI / 180.0;
      else
         up_ev = M_PI / 2.0;
      if (ei > 0)
         down_ev = (ev - evs) * M_PI / 180.0;
      else
         down_ev = -M_PI / 2.0;
      // Calculate the area of the patch band.
      solidAngle = 2.0 * M_PI * (sin (up_ev) - sin (down_ev));
      // Each weight is the area of one patch.
      weights [ei] = solidAngle / hData -> mAzCount [ei];
      // Sum the total surface area covered by the HRIRs.
      sum += solidAngle;
  }
  // Normalize the weights given the total surface coverage.
  for (ei = hData -> mEvStart; ei < hData -> mEvCount; ei ++)
      weights [ei] /= sum;
}

/* Calculate the diffuse-field average from the given magnitude responses of
 * the HRIR set.  Weighting can be applied to compensate for the varying
 * surface area covered by each HRIR.  The final average can then be limited
 * by the specified magnitude range (in positive dB; 0.0 to skip).
 */
static void CalculateDiffuseFieldAverage (const HrirDataT * hData, const int weighted, const double limit, double * dfa) {
  double * weights = NULL;
  uint ei, ai;
  size_t count, step, start, end, m, j, i;
  double weight;

  weights = CreateArray (hData -> mEvCount);
  if (weighted) {
     // Use coverage weighting to calculate the average.
     CalculateDfWeights (hData, weights);
  } else {
     // If coverage weighting is not used, the weights still need to be
     // averaged by the number of HRIRs.
     count = 0;
     for (ei = hData -> mEvStart; ei < hData -> mEvCount; ei ++)
         count += hData -> mAzCount [ei];
     for (ei = hData -> mEvStart; ei < hData -> mEvCount; ei ++)
         weights [ei] = 1.0 / count;
  }
  ei = hData -> mEvStart;
  ai = 0;
  step = hData -> mIrSize;
  start = hData -> mEvOffset [ei] * step;
  end = hData -> mIrCount * step;
  m = 1 + (hData -> mFftSize / 2);
  for (i = 0; i < m; i ++)
      dfa [i] = 0.0;
  for (j = start; j < end; j += step) {
      // Get the weight for this HRIR's contribution.
      weight = weights [ei];
      // Add this HRIR's weighted power average to the total.
      for (i = 0; i < m; i ++)
          dfa [i] += weight * hData -> mHrirs [j + i] * hData -> mHrirs [j + i];
      // Determine the next weight to use.
      ai ++;
      if (ai >= hData -> mAzCount [ei]) {
         ei ++;
         ai = 0;
      }
  }
  // Finish the average calculation and keep it from being too small.
  for (i = 0; i < m; i ++)
      dfa [i] = fmax (sqrt (dfa [i]), EPSILON);
  // Apply a limit to the magnitude range of the diffuse-field average if
  // desired.
  if (limit > 0.0)
     LimitMagnitudeResponse (hData -> mFftSize, limit, dfa, dfa);
  DestroyArray (weights);
}

// Perform diffuse-field equalization on the magnitude responses of the HRIR
// set using the given average response.
static void DiffuseFieldEqualize (const double * dfa, const HrirDataT * hData) {
  size_t step, start, end, m, j, i;

  step = hData -> mIrSize;
  start = hData -> mEvOffset [hData -> mEvStart] * step;
  end = hData -> mIrCount * step;
  m = 1 + (hData -> mFftSize / 2);
  for (j = start; j < end; j += step) {
      for (i = 0; i < m; i ++)
          hData -> mHrirs [j + i] /= dfa [i];
  }
}

// Perform minimum-phase reconstruction using the magnitude responses of the
// HRIR set.
static void ReconstructHrirs (const HrirDataT * hData) {
  double * re = NULL, * im = NULL;
  size_t step, start, end, n, j, i;

  step = hData -> mIrSize;
  start = hData -> mEvOffset [hData -> mEvStart] * step;
  end = hData -> mIrCount * step;
  n = hData -> mFftSize;
  re = CreateArray (n);
  im = CreateArray (n);
  for (j = start; j < end; j += step) {
      MinimumPhase (n, & hData -> mHrirs [j], re, im);
      FftInverse (n, re, im, re, im);
      for (i = 0; i < hData -> mIrPoints; i ++)
          hData -> mHrirs [j + i] = re [i];
  }
  DestroyArray (im);
  DestroyArray (re);
}

/* Given an elevation index and an azimuth, calculate the indices of the two
 * HRIRs that bound the coordinate along with a factor for calculating the
 * continous HRIR using interpolation.
 */
static void CalcAzIndices (const HrirDataT * hData, const uint ei, const double az, uint * j0, uint * j1, double * jf) {
  double af;
  uint ai;

  af = ((2.0 * M_PI) + az) * hData -> mAzCount [ei] / (2.0 * M_PI);
  ai = ((uint) af) % hData -> mAzCount [ei];
  af -= floor (af);
  (* j0) = hData -> mEvOffset [ei] + ai;
  (* j1) = hData -> mEvOffset [ei] + ((ai + 1) % hData -> mAzCount [ei]);
  (* jf) = af;
}

/* Attempt to synthesize any missing HRIRs at the bottom elevations.  Right
 * now this just blends the lowest elevation HRIRs together and applies some
 * attenuation and high frequency damping.  It is a simple, if inaccurate
 * model.
 */
static void SynthesizeHrirs (HrirDataT * hData) {
  uint oi, a, e;
  size_t step, n, i, j;
  double of;
  size_t j0, j1;
  double jf;
  double lp [4], s0, s1;

  if (hData -> mEvStart <= 0)
     return;
  step = hData -> mIrSize;
  oi = hData -> mEvStart;
  n = hData -> mIrPoints;
  for (i = 0; i < n; i ++)
      hData -> mHrirs [i] = 0.0;
  for (a = 0; a < hData -> mAzCount [oi]; a ++) {
      j = (hData -> mEvOffset [oi] + a) * step;
      for (i = 0; i < n; i ++)
          hData -> mHrirs [i] += hData -> mHrirs [j + i] / hData -> mAzCount [oi];
  }
  for (e = 1; e < hData -> mEvStart; e ++) {
      of = ((double) e) / hData -> mEvStart;
      for (a = 0; a < hData -> mAzCount [e]; a ++) {
          j = (hData -> mEvOffset [e] + a) * step;
          CalcAzIndices (hData, oi, a * 2.0 * M_PI / hData -> mAzCount [e], & j0, & j1, & jf);
          j0 *= step;
          j1 *= step;
          lp [0] = 0.0;
          lp [1] = 0.0;
          lp [2] = 0.0;
          lp [3] = 0.0;
          for (i = 0; i < n; i ++) {
              s0 = hData -> mHrirs [i];
              s1 = Lerp (hData -> mHrirs [j0 + i], hData -> mHrirs [j1 + i], jf);
              s0 = Lerp (s0, s1, of);
              lp [0] = Lerp (s0, lp [0], 0.15 - (0.15 * of));
              lp [1] = Lerp (lp [0], lp [1], 0.15 - (0.15 * of));
              lp [2] = Lerp (lp [1], lp [2], 0.15 - (0.15 * of));
              lp [3] = Lerp (lp [2], lp [3], 0.15 - (0.15 * of));
              hData -> mHrirs [j + i] = lp [3];
          }
      }
  }
  lp [0] = 0.0;
  lp [1] = 0.0;
  lp [2] = 0.0;
  lp [3] = 0.0;
  for (i = 0; i < n; i ++) {
      s0 = hData -> mHrirs [i];
      lp [0] = Lerp (s0, lp [0], 0.15);
      lp [1] = Lerp (lp [0], lp [1], 0.15);
      lp [2] = Lerp (lp [1], lp [2], 0.15);
      lp [3] = Lerp (lp [2], lp [3], 0.15);
      hData -> mHrirs [i] = lp [3];
  }
  hData -> mEvStart = 0;
}

// The following routines assume a full set of HRIRs for all elevations.

// Normalize the HRIR set and slightly attenuate the result.
static void NormalizeHrirs (const HrirDataT * hData) {
  size_t step, end, n, j, i;
  double maxLevel;

  step = hData -> mIrSize;
  end = hData -> mIrCount * step;
  n = hData -> mIrPoints;
  maxLevel = 0.0;
  for (j = 0; j < end; j += step) {
      for (i = 0; i < n; i ++)
          maxLevel = fmax (fabs (hData -> mHrirs [j + i]), maxLevel);
  }
  maxLevel = 1.01 * maxLevel;
  for (j = 0; j < end; j += step) {
      for (i = 0; i < n; i ++)
          hData -> mHrirs [j + i] /= maxLevel;
  }
}

// Calculate the left-ear time delay using a spherical head model.
static double CalcLTD (const double ev, const double az, const double rad, const double dist) {
  double azp, dlp, l, al;

  azp = asin (cos (ev) * sin (az));
  dlp = sqrt ((dist * dist) + (rad * rad) + (2.0 * dist * rad * sin (azp)));
  l = sqrt ((dist * dist) - (rad * rad));
  al = (0.5 * M_PI) + azp;
  if (dlp > l)
     dlp = l + (rad * (al - acos (rad / dist)));
  return (dlp / 343.3);
}

// Calculate the effective head-related time delays for the each HRIR, now
// that they are minimum-phase.
static void CalculateHrtds (HrirDataT * hData) {
  double minHrtd, maxHrtd;
  uint e, a, j;
  double t;

  minHrtd = 1000.0;
  maxHrtd = -1000.0;
  for (e = 0; e < hData -> mEvCount; e ++) {
      for (a = 0; a < hData -> mAzCount [e]; a ++) {
          j = hData -> mEvOffset [e] + a;
          t = CalcLTD ((-90.0 + (e * 180.0 / (hData -> mEvCount - 1))) * M_PI / 180.0,
                       (a * 360.0 / hData -> mAzCount [e]) * M_PI / 180.0,
                       hData -> mRadius, hData -> mDistance);
          hData -> mHrtds [j] = t;
          maxHrtd = fmax (t, maxHrtd);
          minHrtd = fmin (t, minHrtd);
      }
  }
  maxHrtd -= minHrtd;
  for (j = 0; j < hData -> mIrCount; j ++)
      hData -> mHrtds [j] -= minHrtd;
  hData -> mMaxHrtd = maxHrtd;
}

// Store the OpenAL Soft HRTF data set.
static int StoreMhr (const HrirDataT * hData, const char * filename) {
  FILE * fp = NULL;
  uint e;
  size_t step, end, n, j, i;
  int hpHist, v;

  if ((fp = fopen (filename, "wb")) == NULL) {
     fprintf (stderr, "Error:  Could not open MHR file '%s'.\n", filename);
     return (0);
  }
  if (! WriteAscii (MHR_FORMAT, fp, filename))
     return (0);
  if (! WriteBin4 (BO_LITTLE, 4, (uint4) hData -> mIrRate, fp, filename))
     return (0);
  if (! WriteBin4 (BO_LITTLE, 1, (uint4) hData -> mIrPoints, fp, filename))
     return (0);
  if (! WriteBin4 (BO_LITTLE, 1, (uint4) hData -> mEvCount, fp, filename))
     return (0);
  for (e = 0; e < hData -> mEvCount; e ++) {
      if (! WriteBin4 (BO_LITTLE, 1, (uint4) hData -> mAzCount [e], fp, filename))
         return (0);
  }
  step = hData -> mIrSize;
  end = hData -> mIrCount * step;
  n = hData -> mIrPoints;
  srand (0x31DF840C);
  for (j = 0; j < end; j += step) {
      hpHist = 0;
      for (i = 0; i < n; i ++) {
          v = HpTpdfDither (32767.0 * hData -> mHrirs [j + i], & hpHist);
          if (! WriteBin4 (BO_LITTLE, 2, (uint4) v, fp, filename))
             return (0);
      }
  }
  for (j = 0; j < hData -> mIrCount; j ++) {
//      v = (int) fmin (round (44100.0 * hData -> mHrtds [j]), MAX_HRTD);
      v = (int) fmin (hData -> mHrtds [j], MAX_HRTD);
      if (! WriteBin4 (BO_LITTLE, 1, (uint4) v, fp, filename))
         return (0);
  }
  fclose (fp);
  return (1);
}

// Store the OpenAL Soft built-in table.
static int StoreTable (const HrirDataT * hData, const char * filename) {
  FILE * fp = NULL;
  size_t step, end, n, j, i;
  int hpHist, v;
  char text [128 + 1];

  if ((fp = fopen (filename, "wb")) == NULL) {
     fprintf (stderr, "Error:  Could not open table file '%s'.\n", filename);
     return (0);
  }
  snprintf (text, 128, "/* Elevation metrics */\n"
                       "static const ALubyte defaultAzCount[%u] = { ", hData -> mEvCount);
  if (! WriteAscii (text, fp, filename))
     return (0);
  for (i = 0; i < hData -> mEvCount; i ++) {
      snprintf (text, 128, "%u, ", hData -> mAzCount [i]);
      if (! WriteAscii (text, fp, filename))
         return (0);
  }
  snprintf (text, 128, "};\n"
                       "static const ALushort defaultEvOffset[%u] = { ", hData -> mEvCount);
  if (! WriteAscii (text, fp, filename))
     return (0);
  for (i = 0; i < hData -> mEvCount; i ++) {
      snprintf (text, 128, "%u, ", hData -> mEvOffset [i]);
      if (! WriteAscii (text, fp, filename))
         return (0);
  }
  step = hData -> mIrSize;
  end = hData -> mIrCount * step;
  n = hData -> mIrPoints;
  snprintf (text, 128, "};\n\n"
                       "/* HRIR Coefficients */\n"
                       "static const ALshort defaultCoeffs[%u] =\n{\n", hData -> mIrCount * n);
  if (! WriteAscii (text, fp, filename))
     return (0);
  srand (0x31DF840C);
  for (j = 0; j < end; j += step) {
      if (! WriteAscii ("    ", fp, filename))
         return (0);
      hpHist = 0;
      for (i = 0; i < n; i ++) {
          v = HpTpdfDither (32767.0 * hData -> mHrirs [j + i], & hpHist);
          snprintf (text, 128, "%+d, ", v);
          if (! WriteAscii (text, fp, filename))
             return (0);
      }
      if (! WriteAscii ("\n", fp, filename))
         return (0);
  }
  snprintf (text, 128, "};\n\n"
                       "/* HRIR Delays */\n"
                       "static const ALubyte defaultDelays[%d] =\n{\n"
                       "    ", hData -> mIrCount);
  if (! WriteAscii (text, fp, filename))
     return (0);
  for (j = 0; j < hData -> mIrCount; j ++) {
      v = (int) fmin (round (44100.0 * hData -> mHrtds [j]), MAX_HRTD);
      snprintf (text, 128, "%d, ", v);
      if (! WriteAscii (text, fp, filename))
         return (0);
  }
  if (! WriteAscii ("\n};\n\n"
                    "/* Default HRTF Definition */\n", fp, filename))
     return (0);
  snprintf (text, 128, "static const struct Hrtf DefaultHrtf = {\n"
                       "    %u, %u, %u, defaultAzCount, defaultEvOffset,\n",
                       hData -> mIrRate, hData -> mIrPoints, hData -> mEvCount);
  if (! WriteAscii (text, fp, filename))
     return (0);
  if (! WriteAscii ("    defaultCoeffs, defaultDelays, NULL\n"
                    "};\n", fp, filename))
     return (0);
  fclose (fp);
  return (1);
}

// Process the data set definition to read and validate the data set metrics.
static int ProcessMetrics (TokenReaderT * tr, const size_t fftSize, const size_t truncSize, HrirDataT * hData) {
  char ident [MAX_IDENT_LEN + 1];
  uint line, col;
  int intVal;
  size_t points;
  double fpVal;
  int hasRate = 0, hasPoints = 0, hasAzimuths = 0;
  int hasRadius = 0, hasDistance = 0;

  while (! (hasRate && hasPoints && hasAzimuths && hasRadius && hasDistance)) {
    TrIndication (tr, & line, & col);
    if (! TrReadIdent (tr, MAX_IDENT_LEN, ident))
       return (0);
    if (strcasecmp (ident, "rate") == 0) {
       if (hasRate) {
          TrErrorAt (tr, line, col, "Redefinition of 'rate'.\n");
          return (0);
       }
       if (! TrReadOperator (tr, "="))
          return (0);
       if (! TrReadInt (tr, MIN_RATE, MAX_RATE, & intVal))
          return (0);
       hData -> mIrRate = intVal;
       hasRate = 1;
    } else if (strcasecmp (ident, "points") == 0) {
       if (hasPoints) {
          TrErrorAt (tr, line, col, "Redefinition of 'points'.\n");
          return (0);
       }
       if (! TrReadOperator (tr, "="))
          return (0);
       TrIndication (tr, & line, & col);
       if (! TrReadInt (tr, MIN_POINTS, MAX_POINTS, & intVal))
          return (0);
       points = (size_t) intVal;
       if ((fftSize > 0) && (points > fftSize)) {
          TrErrorAt (tr, line, col, "Value exceeds the overriden FFT size.\n");
          return (0);
       }
       if (points < truncSize) {
          TrErrorAt (tr, line, col, "Value is below the truncation size.\n");
          return (0);
       }
       hData -> mIrPoints = points;
       hData -> mFftSize = fftSize;
       if (fftSize <= 0) {
          points = 1;
          while (points < (4 * hData -> mIrPoints))
            points <<= 1;
          hData -> mFftSize = points;
          hData -> mIrSize = 1 + (points / 2);
       } else {
          hData -> mFftSize = fftSize;
          hData -> mIrSize = 1 + (fftSize / 2);
          if (points > hData -> mIrSize)
             hData -> mIrSize = points;
       }
       hasPoints = 1;
    } else if (strcasecmp (ident, "azimuths") == 0) {
       if (hasAzimuths) {
          TrErrorAt (tr, line, col, "Redefinition of 'azimuths'.\n");
          return (0);
       }
       if (! TrReadOperator (tr, "="))
          return (0);
       hData -> mIrCount = 0;
       hData -> mEvCount = 0;
       hData -> mEvOffset [0] = 0;
       for (;;) {
           if (! TrReadInt (tr, MIN_AZ_COUNT, MAX_AZ_COUNT, & intVal))
              return (0);
           hData -> mAzCount [hData -> mEvCount] = intVal;
           hData -> mIrCount += intVal;
           hData -> mEvCount ++;
           if (! TrIsOperator (tr, ","))
              break;
           if (hData -> mEvCount >= MAX_EV_COUNT) {
              TrError (tr, "Exceeded the maximum of %d elevations.\n", MAX_EV_COUNT);
              return (0);
           }
           hData -> mEvOffset [hData -> mEvCount] = hData -> mEvOffset [hData -> mEvCount - 1] + intVal;
           TrReadOperator (tr, ",");
       }
       if (hData -> mEvCount < MIN_EV_COUNT) {
          TrErrorAt (tr, line, col, "Did not reach the minimum of %d azimuth counts.\n", MIN_EV_COUNT);
          return (0);
       }
       hasAzimuths = 1;
    } else if (strcasecmp (ident, "radius") == 0) {
       if (hasRadius) {
          TrErrorAt (tr, line, col, "Redefinition of 'radius'.\n");
          return (0);
       }
       if (! TrReadOperator (tr, "="))
          return (0);
       if (! TrReadFloat (tr, MIN_RADIUS, MAX_RADIUS, & fpVal))
          return (0);
       hData -> mRadius = fpVal;
       hasRadius = 1;
    } else if (strcasecmp (ident, "distance") == 0) {
       if (hasDistance) {
          TrErrorAt (tr, line, col, "Redefinition of 'distance'.\n");
          return (0);
       }
       if (! TrReadOperator (tr, "="))
          return (0);
       if (! TrReadFloat (tr, MIN_DISTANCE, MAX_DISTANCE, & fpVal))
          return (0);
       hData -> mDistance = fpVal;
       hasDistance = 1;
    } else {
       TrErrorAt (tr, line, col, "Expected a metric name.\n");
       return (0);
    }
    TrSkipWhitespace (tr);
  }
  return (1);
}

// Parse an index pair from the data set definition.
static int ReadIndexPair (TokenReaderT * tr, const HrirDataT * hData, uint * ei, uint * ai) {
  int intVal;

  if (! TrReadInt (tr, 0, hData -> mEvCount, & intVal))
     return (0);
  (* ei) = (uint) intVal;
  if (! TrReadOperator (tr, ","))
     return (0);
  if (! TrReadInt (tr, 0, hData -> mAzCount [(* ei)], & intVal))
     return (0);
  (* ai) = (uint) intVal;
  return (1);
}

// Match the source format from a given identifier.
static SourceFormatT MatchSourceFormat (const char * ident) {
  if (strcasecmp (ident, "wave") == 0)
     return (SF_WAVE);
  else if (strcasecmp (ident, "bin_le") == 0)
     return (SF_BIN_LE);
  else if (strcasecmp (ident, "bin_be") == 0)
     return (SF_BIN_BE);
  else if (strcasecmp (ident, "ascii") == 0)
     return (SF_ASCII);
  return (SF_NONE);
}

// Match the source element type from a given identifier.
static ElementTypeT MatchElementType (const char * ident) {
  if (strcasecmp (ident, "int") == 0)
     return (ET_INT);
  else if (strcasecmp (ident, "fp") == 0)
     return (ET_FP);
  return (ET_NONE);
}

// Parse and validate a source reference from the data set definition.
static int ReadSourceRef (TokenReaderT * tr, SourceRefT * src) {
  uint line, col;
  char ident [MAX_IDENT_LEN + 1];
  int intVal;

  TrIndication (tr, & line, & col);
  if (! TrReadIdent (tr, MAX_IDENT_LEN, ident))
     return (0);
  src -> mFormat = MatchSourceFormat (ident);
  if (src -> mFormat == SF_NONE) {
     TrErrorAt (tr, line, col, "Expected a source format.\n");
     return (0);
  }
  if (! TrReadOperator (tr, "("))
     return (0);
  if (src -> mFormat == SF_WAVE) {
     if (! TrReadInt (tr, 0, MAX_WAVE_CHANNELS, & intVal))
        return (0);
     src -> mType = ET_NONE;
     src -> mSize = 0;
     src -> mBits = 0;
     src -> mChannel = (uint) intVal;
     src -> mSkip = 0;
  } else {
     TrIndication (tr, & line, & col);
     if (! TrReadIdent (tr, MAX_IDENT_LEN, ident))
        return (0);
     src -> mType = MatchElementType (ident);
     if (src -> mType == ET_NONE) {
        TrErrorAt (tr, line, col, "Expected a source element type.\n");
        return (0);
     }
     if ((src -> mFormat == SF_BIN_LE) || (src -> mFormat == SF_BIN_BE)) {
        if (! TrReadOperator (tr, ","))
           return (0);
        if (src -> mType == ET_INT) {
           if (! TrReadInt (tr, MIN_BIN_SIZE, MAX_BIN_SIZE, & intVal))
              return (0);
           src -> mSize = intVal;
           if (TrIsOperator (tr, ",")) {
              TrReadOperator (tr, ",");
              TrIndication (tr, & line, & col);
              if (! TrReadInt (tr, 0x80000000, 0x7FFFFFFF, & intVal))
                 return (0);
              if ((abs (intVal) < MIN_BIN_BITS) || ((uint)abs(intVal) > (8 * src -> mSize))) {
                 TrErrorAt (tr, line, col, "Expected a value of (+/-) %d to %d.\n", MIN_BIN_BITS, 8 * src -> mSize);
                 return (0);
              }
              src -> mBits = intVal;
           } else {
              src -> mBits = 8 * src -> mSize;
           }
        } else {
           TrIndication (tr, & line, & col);
           if (! TrReadInt (tr, 0x80000000, 0x7FFFFFFF, & intVal))
              return (0);
           if ((intVal != 4) && (intVal != 8)) {
              TrErrorAt (tr, line, col, "Expected a value of 4 or 8.\n");
              return (0);
           }
           src -> mSize = (uint) intVal;
           src -> mBits = 0;
        }
     } else if ((src -> mFormat == SF_ASCII) && (src -> mType == ET_INT)) {
        if (! TrReadOperator (tr, ","))
           return (0);
        if (! TrReadInt (tr, MIN_ASCII_BITS, MAX_ASCII_BITS, & intVal))
           return (0);
        src -> mSize = 0;
        src -> mBits = intVal;
     } else {
        src -> mSize = 0;
        src -> mBits = 0;
     }
     if (TrIsOperator (tr, ";")) {
        TrReadOperator (tr, ";");
        if (! TrReadInt (tr, 0, 0x7FFFFFFF, & intVal))
           return (0);
        src -> mSkip = (uint) intVal;
     } else {
        src -> mSkip = 0;
     }
  }
  if (! TrReadOperator (tr, ")"))
     return (0);
  if (TrIsOperator (tr, "@")) {
     TrReadOperator (tr, "@");
     if (! TrReadInt (tr, 0, 0x7FFFFFFF, & intVal))
        return (0);
     src -> mOffset = (uint) intVal;
  } else {
     src -> mOffset = 0;
  }
  if (! TrReadOperator (tr, ":"))
     return (0);
  if (! TrReadString (tr, MAX_PATH_LEN, src -> mPath))
     return (0);
  return (1);
}

// Process the list of sources in the data set definition.
static int ProcessSources (TokenReaderT * tr, HrirDataT * hData) {
  uint * setCount = NULL, * setFlag = NULL;
  double * hrir = NULL;
  uint line, col, ei, ai;
  SourceRefT src;
  double factor;

  setCount = (uint *) calloc (hData -> mEvCount, sizeof (uint));
  setFlag = (uint *) calloc (hData -> mIrCount, sizeof (uint));
  hrir = CreateArray (hData -> mIrPoints);
  while (TrIsOperator (tr, "[")) {
    TrIndication (tr, & line, & col);
    TrReadOperator (tr, "[");
    if (ReadIndexPair (tr, hData, & ei, & ai)) {
       if (TrReadOperator (tr, "]")) {
          if (! setFlag [hData -> mEvOffset [ei] + ai]) {
             if (TrReadOperator (tr, "=")) {
                factor = 1.0;
                for (;;) {
                    if (ReadSourceRef (tr, & src)) {
                       if (LoadSource (& src, hData -> mIrRate, hData -> mIrPoints, hrir)) {
                          AverageHrirMagnitude (hrir, 1.0 / factor, ei, ai, hData);
                          factor += 1.0;
                          if (! TrIsOperator (tr, "+"))
                             break;
                          TrReadOperator (tr, "+");
                          continue;
                       }
                    }
                    DestroyArray (hrir);
                    free (setFlag);
                    free (setCount);
                    return (0);
                }
                setFlag [hData -> mEvOffset [ei] + ai] = 1;
                setCount [ei] ++;
                continue;
             }
          } else {
             TrErrorAt (tr, line, col, "Redefinition of source.\n");
          }
       }
    }
    DestroyArray (hrir);
    free (setFlag);
    free (setCount);
    return (0);
  }
  ei = 0;
  while ((ei < hData -> mEvCount) && (setCount [ei] < 1))
    ei ++;
  if (ei < hData -> mEvCount) {
     hData -> mEvStart = ei;
     while ((ei < hData -> mEvCount) && (setCount [ei] == hData -> mAzCount [ei]))
       ei ++;
     if (ei >= hData -> mEvCount) {
        if (! TrLoad (tr)) {
           DestroyArray (hrir);
           free (setFlag);
           free (setCount);
           return (1);
        } else {
           TrError (tr, "Errant data at end of source list.\n");
        }
     } else {
        TrError (tr, "Missing sources for elevation index %d.\n", ei);
     }
  } else {
     TrError (tr, "Missing source references.\n");
  }
  DestroyArray (hrir);
  free (setFlag);
  free (setCount);
  return (0);
}

/* Parse the data set definition and process the source data, storing the
 * resulting data set as desired.  If the input name is NULL it will read
 * from standard input.
 */
static int ProcessDefinition (const char * inName, const size_t fftSize, const int equalize, const int surface, const double limit, const size_t truncSize, const OutputFormatT outFormat, const char * outName) {
  FILE * fp = NULL;
  TokenReaderT tr;
  HrirDataT hData;
  double * dfa = NULL;
  char rateStr [8 + 1], expName [MAX_PATH_LEN];

  hData.mIrRate   = 0;
  hData.mIrPoints = 0;
  hData.mFftSize  = 0;
  hData.mIrSize   = 0;
  hData.mIrCount  = 0;
  hData.mEvCount  = 0;
  hData.mRadius   = 0;
  hData.mDistance = 0;

  fprintf (stdout, "Reading HRIR definition...\n");
  if (inName != NULL) {
     fp = fopen (inName, "r");
     if (fp == NULL) {
        fprintf (stderr, "Error:  Could not open definition file '%s'\n", inName);
        return (0);
     }
     TrSetup (fp, inName, & tr);
  } else {
     fp = stdin;
     TrSetup (fp, "<stdin>", & tr);
  }
  if (! ProcessMetrics (& tr, fftSize, truncSize, & hData)) {
     if (inName != NULL)
        fclose (fp);
     return (0);
  }
  hData . mHrirs = CreateArray (hData . mIrCount * hData . mIrSize);
  hData . mHrtds = CreateArray (hData . mIrCount);
  if (! ProcessSources (& tr, & hData)) {
     DestroyArray (hData . mHrtds);
     DestroyArray (hData . mHrirs);
     if (inName != NULL)
        fclose (fp);
     return (0);
  }
  if (inName != NULL)
     fclose (fp);
  if (equalize) {
     dfa = CreateArray (1 + (hData . mFftSize / 2));
     fprintf (stdout, "Calculating diffuse-field average...\n");
     CalculateDiffuseFieldAverage (& hData, surface, limit, dfa);
     fprintf (stdout, "Performing diffuse-field equalization...\n");
     DiffuseFieldEqualize (dfa, & hData);
     DestroyArray (dfa);
  }
  fprintf (stdout, "Performing minimum phase reconstruction...\n");
  ReconstructHrirs (& hData);
  fprintf (stdout, "Truncating minimum-phase HRIRs...\n");
  hData . mIrPoints = truncSize;
  fprintf (stdout, "Synthesizing missing elevations...\n");
  SynthesizeHrirs (& hData);
  fprintf (stdout, "Normalizing final HRIRs...\n");
  NormalizeHrirs (& hData);
  fprintf (stdout, "Calculating impulse delays...\n");
  CalculateHrtds (& hData);
  snprintf (rateStr, 8, "%u", hData . mIrRate);
  StrSubst (outName, "%r", rateStr, MAX_PATH_LEN, expName);
  switch (outFormat) {
    case OF_MHR :
      fprintf (stdout, "Creating MHR data set file...\n");
      if (! StoreMhr (& hData, expName))
         return (0);
    break;
    case OF_TABLE :
      fprintf (stderr, "Creating OpenAL Soft table file...\n");
      if (! StoreTable (& hData, expName))
         return (0);
    break;
    default :
    break;
  }
  DestroyArray (hData . mHrtds);
  DestroyArray (hData . mHrirs);
  return (1);
}

// Standard command line dispatch.
int main (const int argc, const char * argv []) {
  const char * inName = NULL, * outName = NULL;
  OutputFormatT outFormat;
  int argi;
  size_t fftSize;
  int equalize, surface;
  double limit;
  size_t truncSize;
  char * end = NULL;

  if (argc < 2) {
     fprintf (stderr, "Error:  No command specified.  See '%s -h' for help.\n", argv [0]);
     return (-1);
  }
  if ((strcmp (argv [1], "--help") == 0) || (strcmp (argv [1], "-h") == 0)) {
     fprintf (stdout, "HRTF Processing and Composition Utility\n\n");
     fprintf (stdout, "Usage:  %s <command> [<option>...]\n\n", argv [0]);
     fprintf (stdout, "Commands:\n");
     fprintf (stdout, " -m, --make-mhr  Makes an OpenAL Soft compatible HRTF data set.\n");
     fprintf (stdout, "                 Defaults output to: ./oalsoft_hrtf_%%r.mhr\n");
     fprintf (stdout, " -t, --make-tab  Makes the built-in table used when compiling OpenAL Soft.\n");
     fprintf (stdout, "                 Defaults output to: ./hrtf_tables.inc\n");
     fprintf (stdout, " -h, --help      Displays this help information.\n\n");
     fprintf (stdout, "Options:\n");
     fprintf (stdout, " -f=<points>     Override the FFT window size (defaults to the first power-\n");
     fprintf (stdout, "                 of-two that fits four times the number of HRIR points).\n");
     fprintf (stdout, " -e={on|off}     Toggle diffuse-field equalization (default: %s).\n", (DEFAULT_EQUALIZE ? "on" : "off"));
     fprintf (stdout, " -s={on|off}     Toggle surface-weighted diffuse-field average (default: %s).\n", (DEFAULT_SURFACE ? "on" : "off"));
     fprintf (stdout, " -l={<dB>|none}  Specify a limit to the magnitude range of the diffuse-field\n");
     fprintf (stdout, "                 average (default: %.2f).\n", DEFAULT_LIMIT);
     fprintf (stdout, " -w=<points>     Specify the size of the truncation window that's applied\n");
     fprintf (stdout, "                 after minimum-phase reconstruction (default: %d).\n", DEFAULT_TRUNCSIZE);
     fprintf (stdout, " -i=<filename>   Specify an HRIR definition file to use (defaults to stdin).\n");
     fprintf (stdout, " -o=<filename>   Specify an output file.  Overrides command-selected default.\n");
     fprintf (stdout, "                 Use of '%%r' will be substituted with the data set sample rate.\n");
     return (0);
  }
  if ((strcmp (argv [1], "--make-mhr") == 0) || (strcmp (argv [1], "-m") == 0)) {
     if (argc > 3)
        outName = argv [3];
     else
        outName = "./oalsoft_hrtf_%r.mhr";
     outFormat = OF_MHR;
  } else if ((strcmp (argv [1], "--make-tab") == 0) || (strcmp (argv [1], "-t") == 0)) {
     if (argc > 3)
        outName = argv [3];
     else
        outName = "./hrtf_tables.inc";
     outFormat = OF_TABLE;
  } else {
     fprintf (stderr, "Error:  Invalid command '%s'.\n", argv [1]);
     return (-1);
  }
  argi = 2;
  fftSize = 0;
  equalize = DEFAULT_EQUALIZE;
  surface = DEFAULT_SURFACE;
  limit = DEFAULT_LIMIT;
  truncSize = DEFAULT_TRUNCSIZE;
  while (argi < argc) {
    if (strncmp (argv [argi], "-f=", 3) == 0) {
       fftSize = strtoul (& argv [argi] [3], & end, 10);
       if ((end [0] != '\0') || (fftSize & (fftSize - 1)) || (fftSize < MIN_FFTSIZE) || (fftSize > MAX_FFTSIZE)) {
          fprintf (stderr, "Error:  Expected a power-of-two value from %d to %d for '-f'.\n", MIN_FFTSIZE, MAX_FFTSIZE);
          return (-1);
       }
    } else if (strncmp (argv [argi], "-e=", 3) == 0) {
       if (strcmp (& argv [argi] [3], "on") == 0) {
          equalize = 1;
       } else if (strcmp (& argv [argi] [3], "off") == 0) {
          equalize = 0;
       } else {
          fprintf (stderr, "Error:  Expected 'on' or 'off' for '-e'.\n");
          return (-1);
       }
    } else if (strncmp (argv [argi], "-s=", 3) == 0) {
       if (strcmp (& argv [argi] [3], "on") == 0) {
          surface = 1;
       } else if (strcmp (& argv [argi] [3], "off") == 0) {
          surface = 0;
       } else {
          fprintf (stderr, "Error:  Expected 'on' or 'off' for '-s'.\n");
          return (-1);
       }
    } else if (strncmp (argv [argi], "-l=", 3) == 0) {
       if (strcmp (& argv [argi] [3], "none") == 0) {
          limit = 0.0;
       } else {
          limit = strtod (& argv [argi] [3], & end);
          if ((end [0] != '\0') || (limit < MIN_LIMIT) || (limit > MAX_LIMIT)) {
             fprintf (stderr, "Error:  Expected 'none' or a value from %.2f to %.2f for '-l'.\n", MIN_LIMIT, MAX_LIMIT);
             return (-1);
          }
       }
    } else if (strncmp (argv [argi], "-w=", 3) == 0) {
       truncSize = strtoul (& argv [argi] [3], & end, 10);
       if ((end [0] != '\0') || (truncSize < MIN_TRUNCSIZE) || (truncSize > MAX_TRUNCSIZE) || (truncSize % MOD_TRUNCSIZE)) {
          fprintf (stderr, "Error:  Expected a value from %d to %d in multiples of %d for '-w'.\n", MIN_TRUNCSIZE, MAX_TRUNCSIZE, MOD_TRUNCSIZE);
          return (-1);
       }
    } else if (strncmp (argv [argi], "-i=", 3) == 0) {
       inName = & argv [argi] [3];
    } else if (strncmp (argv [argi], "-o=", 3) == 0) {
       outName = & argv [argi] [3];
    } else {
       fprintf (stderr, "Error:  Invalid option '%s'.\n", argv [argi]);
       return (-1);
    }
    argi ++;
  }
  if (! ProcessDefinition (inName, fftSize, equalize, surface, limit, truncSize, outFormat, outName))
     return (-1);
  fprintf (stdout, "Operation completed.\n");
  return (0);
}