Move duplicate SOFA-related functions to a reusable library

5 files changed, 355 insertions, 514 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4bc0aeeb..1d847fe9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1393,6 +1393,15 @@ IF(ALSOFT_UTILS)
 
     find_package(MySOFA)
     if(MYSOFA_FOUND)
+        set(SOFA_SUPPORT_SRCS
+            utils/sofa-support.cpp
+            utils/sofa-support.h)
+        add_library(sofa-support STATIC EXCLUDE_FROM_ALL ${SOFA_SUPPORT_SRCS})
+        target_compile_definitions(sofa-support PRIVATE ${CPP_DEFS})
+        target_include_directories(sofa-support PUBLIC ${OpenAL_SOURCE_DIR}/common)
+        target_compile_options(sofa-support PRIVATE ${C_FLAGS})
+        target_link_libraries(sofa-support PUBLIC common MySOFA::MySOFA PRIVATE ${LINKER_FLAGS})
+
         set(MAKEMHR_SRCS
             utils/makemhr/loaddef.cpp
             utils/makemhr/loaddef.h
@@ -1406,17 +1415,17 @@ IF(ALSOFT_UTILS)
         add_executable(makemhr ${MAKEMHR_SRCS})
         target_compile_definitions(makemhr PRIVATE ${CPP_DEFS})
         target_include_directories(makemhr
-            PRIVATE ${OpenAL_SOURCE_DIR}/common ${OpenAL_BINARY_DIR})
+            PRIVATE ${OpenAL_BINARY_DIR} ${OpenAL_SOURCE_DIR}/utils)
         target_compile_options(makemhr PRIVATE ${C_FLAGS})
-        target_link_libraries(makemhr PRIVATE common ${LINKER_FLAGS} MySOFA::MySOFA)
+        target_link_libraries(makemhr PRIVATE ${LINKER_FLAGS} sofa-support)
         set(UTIL_TARGETS ${UTIL_TARGETS} makemhr)
 
         set(SOFAINFO_SRCS  utils/sofa-info.cpp)
         add_executable(sofa-info ${SOFAINFO_SRCS})
         target_compile_definitions(sofa-info PRIVATE ${CPP_DEFS})
-        target_include_directories(sofa-info PRIVATE ${OpenAL_SOURCE_DIR}/common)
+        target_include_directories(sofa-info PRIVATE ${OpenAL_SOURCE_DIR}/utils)
         target_compile_options(sofa-info PRIVATE ${C_FLAGS})
-        target_link_libraries(sofa-info PRIVATE ${LINKER_FLAGS} MySOFA::MySOFA)
+        target_link_libraries(sofa-info PRIVATE ${LINKER_FLAGS} sofa-support)
     endif()
 
     IF(ALSOFT_INSTALL)
diff --git a/utils/makemhr/loadsofa.cpp b/utils/makemhr/loadsofa.cpp
index 886bd6ff..81df8aa4 100644
--- a/utils/makemhr/loadsofa.cpp
+++ b/utils/makemhr/loadsofa.cpp
@@ -24,11 +24,10 @@
 #include "loadsofa.h"
 
 #include <algorithm>
-#include <array>
 #include <atomic>
+#include <chrono>
 #include <cmath>
 #include <cstdio>
-#include <functional>
 #include <future>
 #include <iterator>
 #include <memory>
@@ -37,148 +36,13 @@
 #include <vector>
 
 #include "makemhr.h"
+#include "polyphase_resampler.h"
+#include "sofa-support.h"
 
 #include "mysofa.h"
 
 
-using namespace std::placeholders;
-
-using double3 = std::array<double,3>;
-
-static const char *SofaErrorStr(int err)
-{
-    switch(err)
-    {
-    case MYSOFA_OK: return "OK";
-    case MYSOFA_INVALID_FORMAT: return "Invalid format";
-    case MYSOFA_UNSUPPORTED_FORMAT: return "Unsupported format";
-    case MYSOFA_INTERNAL_ERROR: return "Internal error";
-    case MYSOFA_NO_MEMORY: return "Out of memory";
-    case MYSOFA_READ_ERROR: return "Read error";
-    }
-    return "Unknown";
-}
-
-
-/* Produces a sorted array of unique elements from a particular axis of the
- * triplets array.  The filters are used to focus on particular coordinates
- * of other axes as necessary.  The epsilons are used to constrain the
- * equality of unique elements.
- */
-static std::vector<double> GetUniquelySortedElems(const std::vector<double3> &aers,
-    const uint axis, const double *const (&filters)[3], const double (&epsilons)[3])
-{
-    std::vector<double> elems;
-    for(const double3 &aer : aers)
-    {
-        const double elem{aer[axis]};
-
-        uint j;
-        for(j = 0;j < 3;j++)
-        {
-            if(filters[j] && std::abs(aer[j] - *filters[j]) > epsilons[j])
-                break;
-        }
-        if(j < 3)
-            continue;
-
-        auto iter = elems.begin();
-        for(;iter != elems.end();++iter)
-        {
-            const double delta{elem - *iter};
-            if(delta > epsilons[axis]) continue;
-            if(delta >= -epsilons[axis]) break;
-
-            iter = elems.emplace(iter, elem);
-            break;
-        }
-        if(iter == elems.end())
-            elems.emplace_back(elem);
-    }
-    return elems;
-}
-
-/* Given a list of azimuths, this will produce the smallest step size that can
- * uniformly cover the list. Ideally this will be over half, but in degenerate
- * cases this can fall to a minimum of 5 (the lower limit).
- */
-static double GetUniformAzimStep(const double epsilon, const std::vector<double> &elems)
-{
-    if(elems.size() < 5) return 0.0;
-
-    /* Get the maximum count possible, given the first two elements. It would
-     * be impossible to have more than this since the first element must be
-     * included.
-     */
-    uint count{static_cast<uint>(std::ceil(360.0 / (elems[1]-elems[0])))};
-    count = std::min(count, uint{MAX_AZ_COUNT});
-
-    for(;count >= 5;--count)
-    {
-        /* Given the stepping value for this number of elements, check each
-         * multiple to ensure there's a matching element.
-         */
-        const double step{360.0 / count};
-        bool good{true};
-        size_t idx{1u};
-        for(uint mult{1u};mult < count && good;++mult)
-        {
-            const double target{step*mult + elems[0]};
-            while(idx < elems.size() && target-elems[idx] > epsilon)
-                ++idx;
-            good &= (idx < elems.size()) && !(std::abs(target-elems[idx++]) > epsilon);
-        }
-        if(good)
-            return step;
-    }
-    return 0.0;
-}
-
-/* Given a list of elevations, this will produce the smallest step size that
- * can uniformly cover the list. Ideally this will be over half, but in
- * degenerate cases this can fall to a minimum of 5 (the lower limit).
- */
-static double GetUniformElevStep(const double epsilon, std::vector<double> &elems)
-{
-    if(elems.size() < 5) return 0.0;
-
-    /* Reverse the elevations so it increments starting with -90 (flipped from
-     * +90). This makes it easier to work out a proper stepping value.
-     */
-    std::reverse(elems.begin(), elems.end());
-    for(auto &v : elems) v *= -1.0;
-
-    uint count{static_cast<uint>(std::ceil(180.0 / (elems[1]-elems[0])))};
-    count = std::min(count, uint{MAX_EV_COUNT-1u});
-
-    double ret{0.0};
-    for(;count >= 5;--count)
-    {
-        const double step{180.0 / count};
-        bool good{true};
-        size_t idx{1u};
-        /* Elevations don't need to match all multiples if there's not enough
-         * elements to check. Missing elevations can be synthesized.
-         */
-        for(uint mult{1u};mult <= count && idx < elems.size() && good;++mult)
-        {
-            const double target{step*mult + elems[0]};
-            while(idx < elems.size() && target-elems[idx] > epsilon)
-                ++idx;
-            good &= !(idx < elems.size()) || !(std::abs(target-elems[idx++]) > epsilon);
-        }
-        if(good)
-        {
-            ret = step;
-            break;
-        }
-    }
-    /* Re-reverse the elevations to restore the correct order. */
-    for(auto &v : elems) v *= -1.0;
-    std::reverse(elems.begin(), elems.end());
-
-    return ret;
-}
+using uint = unsigned int;
 
 /* Attempts to produce a compatible layout.  Most data sets tend to be
  * uniform and have the same major axis as used by OpenAL Soft's HRTF model.
@@ -190,16 +54,8 @@ static bool PrepareLayout(const uint m, const float *xyzs, HrirDataT *hData)
 {
     fprintf(stdout, "Detecting compatible layout...\n");
 
-    auto aers = std::vector<double3>(m, double3{});
-    for(uint i{0u};i < m;++i)
-    {
-        float vals[3]{xyzs[i*3], xyzs[i*3 + 1], xyzs[i*3 + 2]};
-        mysofa_c2s(&vals[0]);
-        aers[i] = {vals[0], vals[1], vals[2]};
-    }
-
-    auto radii = GetUniquelySortedElems(aers, 2, {}, {0.1, 0.1, 0.001});
-    if(radii.size() > MAX_FD_COUNT)
+    auto fds = GetCompatibleLayout(m, xyzs);
+    if(fds.size() > MAX_FD_COUNT)
     {
         fprintf(stdout, "Incompatible layout (inumerable radii).\n");
         return false;
@@ -209,104 +65,24 @@ static bool PrepareLayout(const uint m, const float *xyzs, HrirDataT *hData)
     uint evCounts[MAX_FD_COUNT]{};
     auto azCounts = std::vector<uint>(MAX_FD_COUNT*MAX_EV_COUNT, 0u);
 
-    auto dist_end = std::copy_if(radii.cbegin(), radii.cend(), std::begin(distances),
-        std::bind(std::greater_equal<double>{}, _1, hData->mRadius));
-    auto fdCount = static_cast<uint>(std::distance(std::begin(distances), dist_end));
-
-    uint ir_total{0u};
-    for(uint fi{0u};fi < fdCount;)
+    uint fi{0u}, ir_total{0u};
+    for(const auto &field : fds)
     {
-        const double dist{distances[fi]};
-        auto elevs = GetUniquelySortedElems(aers, 1, {nullptr, nullptr, &dist},
-            {0.1, 0.1, 0.001});
-
-        /* Remove elevations that don't have a valid set of azimuths. */
-        auto invalid_elev = [&dist,&aers](const double ev) -> bool
-        {
-            auto azims = GetUniquelySortedElems(aers, 0, {nullptr, &ev, &dist}, {0.1, 0.1, 0.001});
-
-            if(std::abs(ev) > 89.999)
-                return azims.size() != 1;
-            if(azims.empty() || !(std::abs(azims[0]) < 0.1))
-                return true;
-            return GetUniformAzimStep(0.1, azims) <= 0.0;
-        };
-        elevs.erase(std::remove_if(elevs.begin(), elevs.end(), invalid_elev), elevs.end());
-
-        double step{GetUniformElevStep(0.1, elevs)};
-        if(step <= 0.0)
-        {
-            fprintf(stdout, "Non-uniform elevations on field distance %f.\n", dist);
-            std::copy(&distances[fi+1], &distances[fdCount], &distances[fi]);
-            --fdCount;
-            continue;
-        }
-
-        uint evStart{0u};
-        for(uint ei{0u};ei < elevs.size();ei++)
-        {
-            if(!(elevs[ei] < 0.0))
-            {
-                fprintf(stdout, "Too many missing elevations on field distance %f.\n", dist);
-                return false;
-            }
-
-            double eif{(90.0+elevs[ei]) / step};
-            const double ev_start{std::round(eif)};
+        distances[fi] = field.mDistance;
+        evCounts[fi] = field.mEvCount;
 
-            if(std::abs(eif - ev_start) < (0.1/step))
-            {
-                evStart = static_cast<uint>(ev_start);
-                break;
-            }
-        }
-
-        const auto evCount = static_cast<uint>(std::round(180.0 / step)) + 1;
-        if(evCount < 5)
+        for(uint ei{0u};ei < field.mEvStart;ei++)
+            azCounts[fi*MAX_EV_COUNT + ei] = field.mAzCounts[field.mEvCount-ei-1];
+        for(uint ei{field.mEvStart};ei < field.mEvCount;ei++)
         {
-            fprintf(stdout, "Too few uniform elevations on field distance %f.\n", dist);
-            std::copy(&distances[fi+1], &distances[fdCount], &distances[fi]);
-            --fdCount;
-            continue;
-        }
-        evCounts[fi] = evCount;
-
-        for(uint ei{evStart};ei < evCount;ei++)
-        {
-            const double ev{-90.0 + ei*180.0/(evCount - 1)};
-            auto azims = GetUniquelySortedElems(aers, 0, {nullptr, &ev, &dist}, {0.1, 0.1, 0.001});
-
-            uint azCount;
-            if(ei == 0 || ei == (evCount-1))
-            {
-                if(azims.size() != 1)
-                {
-                    fprintf(stdout, "Non-singular poles on field distance %f.\n", dist);
-                    return false;
-                }
-                azCount = 1u;
-            }
-            else
-            {
-                step = GetUniformAzimStep(0.1, azims);
-                if(step <= 0.0)
-                {
-                    fprintf(stdout, "Non-uniform azimuths on elevation %f, field distance %f.\n",
-                        ev, dist);
-                    return false;
-                }
-                azCount = static_cast<uint>(std::round(360.0 / step));
-            }
-            azCounts[fi*MAX_EV_COUNT + ei] = azCount;
-            ir_total += azCount;
+            azCounts[fi*MAX_EV_COUNT + ei] = field.mAzCounts[ei];
+            ir_total += field.mAzCounts[ei];
         }
 
-        for(uint ei{0u};ei < evStart;ei++)
-            azCounts[fi*MAX_EV_COUNT + ei] = azCounts[fi*MAX_EV_COUNT + evCount - ei - 1];
         ++fi;
     }
     fprintf(stdout, "Using %u of %u IRs.\n", ir_total, m);
-    return PrepareHrirData(fdCount, distances, evCounts, azCounts.data(), hData) != 0;
+    return PrepareHrirData(fi, distances, evCounts, azCounts.data(), hData) != 0;
 }
 
 
@@ -575,10 +351,6 @@ static bool LoadResponses(MYSOFA_HRTF *sofaHrtf, HrirDataT *hData)
     return load_future.get();
 }
 
-struct MySofaHrtfDeleter {
-    void operator()(MYSOFA_HRTF *ptr) { mysofa_free(ptr); }
-};
-using MySofaHrtfPtr = std::unique_ptr<MYSOFA_HRTF,MySofaHrtfDeleter>;
 
 bool LoadSofaFile(const char *filename, const uint fftSize, const uint truncSize,
     const ChannelModeT chanMode, HrirDataT *hData)
diff --git a/utils/sofa-info.cpp b/utils/sofa-info.cpp
index 81136334..6ab71306 100644
--- a/utils/sofa-info.cpp
+++ b/utils/sofa-info.cpp
@@ -23,46 +23,16 @@
 
 #include <stdio.h>
 
-#include <algorithm>
-#include <array>
-#include <cmath>
 #include <memory>
 #include <vector>
 
-#include <mysofa.h>
-
+#include "sofa-support.h"
 #include "win_main_utf8.h"
 
+#include "mysofa.h"
 
-using uint = unsigned int;
-using double3 = std::array<double,3>;
-
-struct MySofaDeleter {
-    void operator()(MYSOFA_HRTF *sofa) { mysofa_free(sofa); }
-};
-using MySofaHrtfPtr = std::unique_ptr<MYSOFA_HRTF,MySofaDeleter>;
-
-// Per-field measurement info.
-struct HrirFdT {
-    double mDistance{0.0};
-    uint mEvCount{0u};
-    uint mEvStart{0u};
-    std::vector<uint> mAzCounts;
-};
 
-static const char *SofaErrorStr(int err)
-{
-    switch(err)
-    {
-    case MYSOFA_OK: return "OK";
-    case MYSOFA_INVALID_FORMAT: return "Invalid format";
-    case MYSOFA_UNSUPPORTED_FORMAT: return "Unsupported format";
-    case MYSOFA_INTERNAL_ERROR: return "Internal error";
-    case MYSOFA_NO_MEMORY: return "Out of memory";
-    case MYSOFA_READ_ERROR: return "Read error";
-    }
-    return "Unknown";
-}
+using uint = unsigned int;
 
 static void PrintSofaAttributes(const char *prefix, struct MYSOFA_ATTRIBUTE *attribute)
 {
@@ -76,131 +46,10 @@ static void PrintSofaAttributes(const char *prefix, struct MYSOFA_ATTRIBUTE *att
 static void PrintSofaArray(const char *prefix, struct MYSOFA_ARRAY *array)
 {
     PrintSofaAttributes(prefix, array->attributes);
-
     for(uint i{0u};i < array->elements;i++)
         fprintf(stdout, "%s[%u]: %.6f\n", prefix, i, array->values[i]);
 }
 
-/* Produces a sorted array of unique elements from a particular axis of the
- * triplets array.  The filters are used to focus on particular coordinates
- * of other axes as necessary.  The epsilons are used to constrain the
- * equality of unique elements.
- */
-static std::vector<double> GetUniquelySortedElems(const std::vector<double3> &aers,
-    const uint axis, const double *const (&filters)[3], const double (&epsilons)[3])
-{
-    std::vector<double> elems;
-    for(const double3 &aer : aers)
-    {
-        const double elem{aer[axis]};
-
-        uint j;
-        for(j = 0;j < 3;j++)
-        {
-            if(filters[j] && std::abs(aer[j] - *filters[j]) > epsilons[j])
-                break;
-        }
-        if(j < 3)
-            continue;
-
-        auto iter = elems.begin();
-        for(;iter != elems.end();++iter)
-        {
-            const double delta{elem - *iter};
-            if(delta > epsilons[axis]) continue;
-            if(delta >= -epsilons[axis]) break;
-
-            iter = elems.emplace(iter, elem);
-            break;
-        }
-        if(iter == elems.end())
-            elems.emplace_back(elem);
-    }
-    return elems;
-}
-
-/* Given a list of azimuths, this will produce the smallest step size that can
- * uniformly cover the list. Ideally this will be over half, but in degenerate
- * cases this can fall to a minimum of 5 (the lower limit).
- */
-static double GetUniformAzimStep(const double epsilon, const std::vector<double> &elems)
-{
-    if(elems.size() < 5) return 0.0;
-
-    /* Get the maximum count possible, given the first two elements. It would
-     * be impossible to have more than this since the first element must be
-     * included.
-     */
-    uint count{static_cast<uint>(std::ceil(360.0 / (elems[1]-elems[0])))};
-    count = std::min(count, 255u);
-
-    for(;count >= 5;--count)
-    {
-        /* Given the stepping value for this number of elements, check each
-         * multiple to ensure there's a matching element.
-         */
-        const double step{360.0 / count};
-        bool good{true};
-        size_t idx{1u};
-        for(uint mult{1u};mult < count && good;++mult)
-        {
-            const double target{step*mult + elems[0]};
-            while(idx < elems.size() && target-elems[idx] > epsilon)
-                ++idx;
-            good &= (idx < elems.size()) && !(std::abs(target-elems[idx++]) > epsilon);
-        }
-        if(good)
-            return step;
-    }
-    return 0.0;
-}
-
-/* Given a list of elevations, this will produce the smallest step size that
- * can uniformly cover the list. Ideally this will be over half, but in
- * degenerate cases this can fall to a minimum of 5 (the lower limit).
- */
-static double GetUniformElevStep(const double epsilon, std::vector<double> &elems)
-{
-    if(elems.size() < 5) return 0.0;
-
-    /* Reverse the elevations so it increments starting with -90 (flipped from
-     * +90). This makes it easier to work out a proper stepping value.
-     */
-    std::reverse(elems.begin(), elems.end());
-    for(auto &v : elems) v *= -1.0;
-
-    uint count{static_cast<uint>(std::ceil(180.0 / (elems[1]-elems[0])))};
-    count = std::min(count, 255u);
-
-    double ret{0.0};
-    for(;count >= 5;--count)
-    {
-        const double step{180.0 / count};
-        bool good{true};
-        size_t idx{1u};
-        /* Elevations don't need to match all multiples if there's not enough
-         * elements to check. Missing elevations can be synthesized.
-         */
-        for(uint mult{1u};mult <= count && idx < elems.size() && good;++mult)
-        {
-            const double target{step*mult + elems[0]};
-            while(idx < elems.size() && target-elems[idx] > epsilon)
-                ++idx;
-            good &= !(idx < elems.size()) || !(std::abs(target-elems[idx++]) > epsilon);
-        }
-        if(good)
-        {
-            ret = step;
-            break;
-        }
-    }
-    /* Re-reverse the elevations to restore the correct order. */
-    for(auto &v : elems) v *= -1.0;
-    std::reverse(elems.begin(), elems.end());
-
-    return ret;
-}
-
 /* Attempts to produce a compatible layout.  Most data sets tend to be
  * uniform and have the same major axis as used by OpenAL Soft's HRTF model.
  * This will remove outliers and produce a maximally dense layout when
@@ -211,118 +60,7 @@ static void PrintCompatibleLayout(const uint m, const float *xyzs)
 {
     fputc('\n', stdout);
 
-    auto aers = std::vector<double3>(m, double3{});
-    for(uint i{0u};i < m;++i)
-    {
-        float vals[3]{xyzs[i*3], xyzs[i*3 + 1], xyzs[i*3 + 2]};
-        mysofa_c2s(&vals[0]);
-        aers[i] = {vals[0], vals[1], vals[2]};
-    }
-
-    auto radii = GetUniquelySortedElems(aers, 2, {}, {0.1, 0.1, 0.001});
-
-    auto fds = std::vector<HrirFdT>(radii.size());
-    for(size_t fi{0u};fi < radii.size();fi++)
-        fds[fi].mDistance = radii[fi];
-
-    for(uint fi{0u};fi < fds.size();)
-    {
-        const double dist{fds[fi].mDistance};
-        auto elevs = GetUniquelySortedElems(aers, 1, {nullptr, nullptr, &dist}, {0.1, 0.1, 0.001});
-
-        /* Remove elevations that don't have a valid set of azimuths. */
-        auto invalid_elev = [&dist,&aers](const double ev) -> bool
-        {
-            auto azims = GetUniquelySortedElems(aers, 0, {nullptr, &ev, &dist}, {0.1, 0.1, 0.001});
-
-            if(std::abs(ev) > 89.999)
-                return azims.size() != 1;
-            if(azims.empty() || !(std::abs(azims[0]) < 0.1))
-                return true;
-            return GetUniformAzimStep(0.1, azims) <= 0.0;
-        };
-        elevs.erase(std::remove_if(elevs.begin(), elevs.end(), invalid_elev), elevs.end());
-
-        double step{GetUniformElevStep(0.1, elevs)};
-        if(step <= 0.0)
-        {
-            if(elevs.empty())
-                fprintf(stdout, "No usable elevations on field distance %f.\n", dist);
-            else
-            {
-                fprintf(stdout, "Non-uniform elevations on field distance %.3f.\nGot: %+.2f", dist,
-                    elevs[0]);
-                for(size_t ei{1u};ei < elevs.size();++ei)
-                    fprintf(stdout, ", %+.2f", elevs[ei]);
-                fputc('\n', stdout);
-            }
-            fds.erase(fds.begin() + static_cast<ptrdiff_t>(fi));
-            continue;
-        }
-
-        uint evStart{0u};
-        for(uint ei{0u};ei < elevs.size();ei++)
-        {
-            if(!(elevs[ei] < 0.0))
-            {
-                fprintf(stdout, "Too many missing elevations on field distance %f.\n", dist);
-                return;
-            }
-
-            double eif{(90.0+elevs[ei]) / step};
-            const double ev_start{std::round(eif)};
-
-            if(std::abs(eif - ev_start) < (0.1/step))
-            {
-                evStart = static_cast<uint>(ev_start);
-                break;
-            }
-        }
-
-        const auto evCount = static_cast<uint>(std::round(180.0 / step)) + 1;
-        if(evCount < 5)
-        {
-            fprintf(stdout, "Too few uniform elevations on field distance %f.\n", dist);
-            fds.erase(fds.begin() + static_cast<ptrdiff_t>(fi));
-            continue;
-        }
-
-        fds[fi].mEvCount = evCount;
-        fds[fi].mEvStart = evStart;
-        fds[fi].mAzCounts.resize(evCount);
-        auto &azCounts = fds[fi].mAzCounts;
-
-        for(uint ei{evStart};ei < evCount;ei++)
-        {
-            double ev{-90.0 + ei*180.0/(evCount - 1)};
-            auto azims = GetUniquelySortedElems(aers, 0, {nullptr, &ev, &dist}, {0.1, 0.1, 0.001});
-
-            if(ei == 0 || ei == (evCount-1))
-            {
-                if(azims.size() != 1)
-                {
-                    fprintf(stdout, "Non-singular poles on field distance %f.\n", dist);
-                    return;
-                }
-                azCounts[ei] = 1;
-            }
-            else
-            {
-                step = GetUniformAzimStep(0.1, azims);
-                if(step <= 0.0)
-                {
-                    fprintf(stdout, "Non-uniform azimuths on elevation %f, field distance %f.\n",
-                        ev, dist);
-                    return;
-                }
-                azCounts[ei] = static_cast<uint>(std::round(360.0f / step));
-            }
-        }
-
-        for(uint ei{0u};ei < evStart;ei++)
-            azCounts[ei] = azCounts[evCount - ei - 1];
-        ++fi;
-    }
+    auto fds = GetCompatibleLayout(m, xyzs);
     if(fds.empty())
     {
         fprintf(stdout, "No compatible field layouts in SOFA file.\n");
diff --git a/utils/sofa-support.cpp b/utils/sofa-support.cpp
new file mode 100644
index 00000000..e37789d5
--- /dev/null
+++ b/utils/sofa-support.cpp
@@ -0,0 +1,292 @@
+/*
+ * SOFA utility methods for inspecting SOFA file metrics and determining HRTF
+ * utility compatible layouts.
+ *
+ * Copyright (C) 2018-2019  Christopher Fitzgerald
+ * Copyright (C) 2019  Christopher Robinson
+ *
+ * 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
+ */
+
+#include "sofa-support.h"
+
+#include <stdio.h>
+
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <utility>
+#include <vector>
+
+#include "mysofa.h"
+
+
+namespace {
+
+using uint = unsigned int;
+using double3 = std::array<double,3>;
+
+
+/* Produces a sorted array of unique elements from a particular axis of the
+ * triplets array.  The filters are used to focus on particular coordinates
+ * of other axes as necessary.  The epsilons are used to constrain the
+ * equality of unique elements.
+ */
+std::vector<double> GetUniquelySortedElems(const std::vector<double3> &aers, const uint axis,
+    const double *const (&filters)[3], const double (&epsilons)[3])
+{
+    std::vector<double> elems;
+    for(const double3 &aer : aers)
+    {
+        const double elem{aer[axis]};
+
+        uint j;
+        for(j = 0;j < 3;j++)
+        {
+            if(filters[j] && std::abs(aer[j] - *filters[j]) > epsilons[j])
+                break;
+        }
+        if(j < 3)
+            continue;
+
+        auto iter = elems.begin();
+        for(;iter != elems.end();++iter)
+        {
+            const double delta{elem - *iter};
+            if(delta > epsilons[axis]) continue;
+            if(delta >= -epsilons[axis]) break;
+
+            iter = elems.emplace(iter, elem);
+            break;
+        }
+        if(iter == elems.end())
+            elems.emplace_back(elem);
+    }
+    return elems;
+}
+
+/* Given a list of azimuths, this will produce the smallest step size that can
+ * uniformly cover the list. Ideally this will be over half, but in degenerate
+ * cases this can fall to a minimum of 5 (the lower limit).
+ */
+double GetUniformAzimStep(const double epsilon, const std::vector<double> &elems)
+{
+    if(elems.size() < 5) return 0.0;
+
+    /* Get the maximum count possible, given the first two elements. It would
+     * be impossible to have more than this since the first element must be
+     * included.
+     */
+    uint count{static_cast<uint>(std::ceil(360.0 / (elems[1]-elems[0])))};
+    count = std::min(count, 255u);
+
+    for(;count >= 5;--count)
+    {
+        /* Given the stepping value for this number of elements, check each
+         * multiple to ensure there's a matching element.
+         */
+        const double step{360.0 / count};
+        bool good{true};
+        size_t idx{1u};
+        for(uint mult{1u};mult < count && good;++mult)
+        {
+            const double target{step*mult + elems[0]};
+            while(idx < elems.size() && target-elems[idx] > epsilon)
+                ++idx;
+            good &= (idx < elems.size()) && !(std::abs(target-elems[idx++]) > epsilon);
+        }
+        if(good)
+            return step;
+    }
+    return 0.0;
+}
+
+/* Given a list of elevations, this will produce the smallest step size that
+ * can uniformly cover the list. Ideally this will be over half, but in
+ * degenerate cases this can fall to a minimum of 5 (the lower limit).
+ */
+double GetUniformElevStep(const double epsilon, std::vector<double> &elems)
+{
+    if(elems.size() < 5) return 0.0;
+
+    /* Reverse the elevations so it increments starting with -90 (flipped from
+     * +90). This makes it easier to work out a proper stepping value.
+     */
+    std::reverse(elems.begin(), elems.end());
+    for(auto &v : elems) v *= -1.0;
+
+    uint count{static_cast<uint>(std::ceil(180.0 / (elems[1]-elems[0])))};
+    count = std::min(count, 255u);
+
+    double ret{0.0};
+    for(;count >= 5;--count)
+    {
+        const double step{180.0 / count};
+        bool good{true};
+        size_t idx{1u};
+        /* Elevations don't need to match all multiples if there's not enough
+         * elements to check. Missing elevations can be synthesized.
+         */
+        for(uint mult{1u};mult <= count && idx < elems.size() && good;++mult)
+        {
+            const double target{step*mult + elems[0]};
+            while(idx < elems.size() && target-elems[idx] > epsilon)
+                ++idx;
+            good &= !(idx < elems.size()) || !(std::abs(target-elems[idx++]) > epsilon);
+        }
+        if(good)
+        {
+            ret = step;
+            break;
+        }
+    }
+    /* Re-reverse the elevations to restore the correct order. */
+    for(auto &v : elems) v *= -1.0;
+    std::reverse(elems.begin(), elems.end());
+
+    return ret;
+}
+
+} // namespace
+
+
+const char *SofaErrorStr(int err)
+{
+    switch(err)
+    {
+    case MYSOFA_OK: return "OK";
+    case MYSOFA_INVALID_FORMAT: return "Invalid format";
+    case MYSOFA_UNSUPPORTED_FORMAT: return "Unsupported format";
+    case MYSOFA_INTERNAL_ERROR: return "Internal error";
+    case MYSOFA_NO_MEMORY: return "Out of memory";
+    case MYSOFA_READ_ERROR: return "Read error";
+    }
+    return "Unknown";
+}
+
+std::vector<SofaField> GetCompatibleLayout(const size_t m, const float *xyzs)
+{
+    auto aers = std::vector<double3>(m, double3{});
+    for(size_t i{0u};i < m;++i)
+    {
+        float vals[3]{xyzs[i*3], xyzs[i*3 + 1], xyzs[i*3 + 2]};
+        mysofa_c2s(&vals[0]);
+        aers[i] = {vals[0], vals[1], vals[2]};
+    }
+
+    auto radii = GetUniquelySortedElems(aers, 2, {}, {0.1, 0.1, 0.001});
+    std::vector<SofaField> fds;
+    fds.reserve(radii.size());
+
+    for(const double dist : radii)
+    {
+        auto elevs = GetUniquelySortedElems(aers, 1, {nullptr, nullptr, &dist}, {0.1, 0.1, 0.001});
+
+        /* Remove elevations that don't have a valid set of azimuths. */
+        auto invalid_elev = [&dist,&aers](const double ev) -> bool
+        {
+            auto azims = GetUniquelySortedElems(aers, 0, {nullptr, &ev, &dist}, {0.1, 0.1, 0.001});
+
+            if(std::abs(ev) > 89.999)
+                return azims.size() != 1;
+            if(azims.empty() || !(std::abs(azims[0]) < 0.1))
+                return true;
+            return GetUniformAzimStep(0.1, azims) <= 0.0;
+        };
+        elevs.erase(std::remove_if(elevs.begin(), elevs.end(), invalid_elev), elevs.end());
+
+        double step{GetUniformElevStep(0.1, elevs)};
+        if(step <= 0.0)
+        {
+            if(elevs.empty())
+                fprintf(stdout, "No usable elevations on field distance %f.\n", dist);
+            else
+            {
+                fprintf(stdout, "Non-uniform elevations on field distance %.3f.\nGot: %+.2f", dist,
+                    elevs[0]);
+                for(size_t ei{1u};ei < elevs.size();++ei)
+                    fprintf(stdout, ", %+.2f", elevs[ei]);
+                fputc('\n', stdout);
+            }
+            continue;
+        }
+
+        uint evStart{0u};
+        for(uint ei{0u};ei < elevs.size();ei++)
+        {
+            if(!(elevs[ei] < 0.0))
+            {
+                fprintf(stdout, "Too many missing elevations on field distance %f.\n", dist);
+                return fds;
+            }
+
+            double eif{(90.0+elevs[ei]) / step};
+            const double ev_start{std::round(eif)};
+
+            if(std::abs(eif - ev_start) < (0.1/step))
+            {
+                evStart = static_cast<uint>(ev_start);
+                break;
+            }
+        }
+
+        const auto evCount = static_cast<uint>(std::round(180.0 / step)) + 1;
+        if(evCount < 5)
+        {
+            fprintf(stdout, "Too few uniform elevations on field distance %f.\n", dist);
+            continue;
+        }
+
+        SofaField field{};
+        field.mDistance = dist;
+        field.mEvCount = evCount;
+        field.mEvStart = evStart;
+        field.mAzCounts.resize(evCount, 0u);
+        auto &azCounts = field.mAzCounts;
+
+        for(uint ei{evStart};ei < evCount;ei++)
+        {
+            double ev{-90.0 + ei*180.0/(evCount - 1)};
+            auto azims = GetUniquelySortedElems(aers, 0, {nullptr, &ev, &dist}, {0.1, 0.1, 0.001});
+
+            if(ei == 0 || ei == (evCount-1))
+            {
+                if(azims.size() != 1)
+                {
+                    fprintf(stdout, "Non-singular poles on field distance %f.\n", dist);
+                    return fds;
+                }
+                azCounts[ei] = 1;
+            }
+            else
+            {
+                step = GetUniformAzimStep(0.1, azims);
+                if(step <= 0.0)
+                {
+                    fprintf(stdout, "Non-uniform azimuths on elevation %f, field distance %f.\n",
+                        ev, dist);
+                    return fds;
+                }
+                azCounts[ei] = static_cast<uint>(std::round(360.0f / step));
+            }
+        }
+
+        fds.emplace_back(std::move(field));
+    }
+
+    return fds;
+}
diff --git a/utils/sofa-support.h b/utils/sofa-support.h
new file mode 100644
index 00000000..1229f49d
--- /dev/null
+++ b/utils/sofa-support.h
@@ -0,0 +1,30 @@
+#ifndef UTILS_SOFA_SUPPORT_H
+#define UTILS_SOFA_SUPPORT_H
+
+#include <cstddef>
+#include <memory>
+#include <vector>
+
+#include "mysofa.h"
+
+
+struct MySofaDeleter {
+    void operator()(MYSOFA_HRTF *sofa) { mysofa_free(sofa); }
+};
+using MySofaHrtfPtr = std::unique_ptr<MYSOFA_HRTF,MySofaDeleter>;
+
+// Per-field measurement info.
+struct SofaField {
+    using uint = unsigned int;
+
+    double mDistance{0.0};
+    uint mEvCount{0u};
+    uint mEvStart{0u};
+    std::vector<uint> mAzCounts;
+};
+
+const char *SofaErrorStr(int err);
+
+std::vector<SofaField> GetCompatibleLayout(const size_t m, const float *xyzs);
+
+#endif /* UTILS_SOFA_SUPPORT_H */