From d5707b318495829e489196f8c3f02e7cd8085e2e Mon Sep 17 00:00:00 2001
From: Chris Robinson <chris.kcat@gmail.com>
Date: Thu, 25 Nov 2021 19:53:52 -0800
Subject: Use a base for the UhjEncoder/Decoder common properties

---
 core/uhjfilter.cpp | 16 ++++++----------
 core/uhjfilter.h   | 18 ++++++++++--------
 2 files changed, 16 insertions(+), 18 deletions(-)

(limited to 'core')

diff --git a/core/uhjfilter.cpp b/core/uhjfilter.cpp
index f4ef61f8..0e583965 100644
--- a/core/uhjfilter.cpp
+++ b/core/uhjfilter.cpp
@@ -14,11 +14,9 @@
 
 namespace {
 
-static_assert(UhjEncoder::sFilterDelay==UhjDecoder::sFilterDelay, "UHJ filter delays mismatch");
-
 using complex_d = std::complex<double>;
 
-const PhaseShifterT<UhjEncoder::sFilterDelay*2> PShift{};
+const PhaseShifterT<UhjFilterBase::sFilterDelay*2> PShift{};
 
 } // namespace
 
@@ -33,11 +31,11 @@ const PhaseShifterT<UhjEncoder::sFilterDelay*2> PShift{};
  * T = j(-0.1432*W + 0.6511746*X) - 0.7071068*Y
  * Q = 0.9772*Z
  *
- * where j is a wide-band +90 degree phase shift. T is excluded from 2-channel
- * output, and Q is excluded from 2- and 3-channel output.
+ * where j is a wide-band +90 degree phase shift. 3-channel UHJ excludes Q,
+ * while 2-channel excludes Q and T.
  *
- * The phase shift is done using a FIR filter derived from an FFT'd impulse
- * with the desired shift.
+ * The phase shift is done using a linear FIR filter derived from an FFT'd
+ * impulse with the desired shift.
  */
 
 void UhjEncoder::encode(const FloatBufferSpan LeftOut, const FloatBufferSpan RightOut,
@@ -103,9 +101,7 @@ void UhjEncoder::encode(const FloatBufferSpan LeftOut, const FloatBufferSpan Rig
  * Z = 1.023332*Q
  *
  * where j is a +90 degree phase shift. 3-channel UHJ excludes Q, while 2-
- * channel excludes Q and T. The B-Format signal reconstructed from 2-channel
- * UHJ should not be run through a normal B-Format decoder, as it needs
- * different shelf filters.
+ * channel excludes Q and T.
  */
 void UhjDecoder::decode(const al::span<BufferLine> samples, const size_t offset,
     const size_t samplesToDo, const size_t forwardSamples)
diff --git a/core/uhjfilter.h b/core/uhjfilter.h
index e535cfb7..0f4668cd 100644
--- a/core/uhjfilter.h
+++ b/core/uhjfilter.h
@@ -8,12 +8,14 @@
 #include "resampler_limits.h"
 
 
-struct UhjEncoder {
+struct UhjFilterBase {
     /* The filter delay is half it's effective size, so a delay of 128 has a
      * FIR length of 256.
      */
-    constexpr static size_t sFilterDelay{128};
+    static constexpr size_t sFilterDelay{128};
+};
 
+struct UhjEncoder : public UhjFilterBase {
     /* Delays and processing storage for the unfiltered signal. */
     alignas(16) std::array<float,BufferLineSize+sFilterDelay> mS{};
     alignas(16) std::array<float,BufferLineSize+sFilterDelay> mD{};
@@ -35,10 +37,8 @@ struct UhjEncoder {
 };
 
 
-struct UhjDecoder {
-    constexpr static size_t sFilterDelay{128};
-
-    constexpr static size_t sLineSize{BufferLineSize+MaxResamplerPadding+sFilterDelay};
+struct UhjDecoder : public UhjFilterBase {
+    static constexpr size_t sLineSize{BufferLineSize+MaxResamplerPadding+sFilterDelay};
     using BufferLine = std::array<float,sLineSize>;
 
     alignas(16) std::array<float,BufferLineSize+MaxResamplerEdge+sFilterDelay> mS{};
@@ -53,8 +53,10 @@ struct UhjDecoder {
     /**
      * Decodes a 3- or 4-channel UHJ signal into a B-Format signal with FuMa
      * channel ordering and UHJ scaling. For 3-channel, the 3rd channel may be
-     * attenuated by 'n', where 0 <= n <= 1. So 2-channel UHJ can be decoded by
-     * leaving the 3rd channel input silent (n=0).
+     * attenuated by 'n', where 0 <= n <= 1. So to decode 2-channel UHJ, supply
+     * 3 channels with the 3rd channel silent (n=0). The B-Format signal
+     * reconstructed from 2-channel UHJ should not be run through a normal
+     * B-Format decoder, as it needs different shelf filters.
      */
     void decode(const al::span<BufferLine> samples, const size_t offset, const size_t samplesToDo,
         const size_t forwardSamples);
-- 
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