From 5dede763fff06ea0c4084bd636607bb786696a0a Mon Sep 17 00:00:00 2001
From: Olli <oparviai@iki.fi>
Date: Sun, 23 Feb 2025 12:54:41 +0200
Subject: [PATCH] Refactor pow() usage

Refactor pow() usage:
- use base of 0.5^k instead of 1/(2^k)
- skip pow if using INTEGER_SAMPLES
---
 source/SoundTouch/BPMDetect.cpp     |  2 +-
 source/SoundTouch/FIRFilter.cpp     | 17 ++++++++---------
 source/SoundTouch/FIRFilter.h       |  3 ---
 source/SoundTouch/sse_optimized.cpp | 11 ++++-------
 4 files changed, 13 insertions(+), 20 deletions(-)

diff --git a/source/SoundTouch/BPMDetect.cpp b/source/SoundTouch/BPMDetect.cpp
index f7995c8..43763f7 100644
--- a/source/SoundTouch/BPMDetect.cpp
+++ b/source/SoundTouch/BPMDetect.cpp
@@ -301,7 +301,7 @@ void BPMDetect::updateXCorr(int process_samples)
     pBuffer = buffer->ptrBegin();
 
     // calculate decay factor for xcorr filtering
-    float xcorr_decay = (float)pow(0.5, 1.0 / (XCORR_DECAY_TIME_CONSTANT * TARGET_SRATE / process_samples));
+    float xcorr_decay = (float)pow(0.5, process_samples / (XCORR_DECAY_TIME_CONSTANT * TARGET_SRATE));
 
     // prescale pbuffer
     float tmp[XCORR_UPDATE_SEQUENCE];
diff --git a/source/SoundTouch/FIRFilter.cpp b/source/SoundTouch/FIRFilter.cpp
index 20f9311..c8cac30 100644
--- a/source/SoundTouch/FIRFilter.cpp
+++ b/source/SoundTouch/FIRFilter.cpp
@@ -56,7 +56,6 @@ using namespace soundtouch;
 FIRFilter::FIRFilter()
 {
     resultDivFactor = 0;
-    resultDivider = 0;
     length = 0;
     lengthDiv8 = 0;
     filterCoeffs = nullptr;
@@ -207,24 +206,24 @@ void FIRFilter::setCoefficients(const SAMPLETYPE *coeffs, uint newLength, uint u
     assert(newLength > 0);
     if (newLength % 8) ST_THROW_RT_ERROR("FIR filter length not divisible by 8");
 
-    #ifdef SOUNDTOUCH_FLOAT_SAMPLES
-        // scale coefficients already here if using floating samples
-        double scale = 1.0 / resultDivider;
-    #else
-        short scale = 1;
-    #endif
-
     lengthDiv8 = newLength / 8;
     length = lengthDiv8 * 8;
     assert(length == newLength);
 
     resultDivFactor = uResultDivFactor;
-    resultDivider = (SAMPLETYPE)::pow(2.0, (int)resultDivFactor);
 
     delete[] filterCoeffs;
     filterCoeffs = new SAMPLETYPE[length];
     delete[] filterCoeffsStereo;
     filterCoeffsStereo = new SAMPLETYPE[length*2];
+
+#ifdef SOUNDTOUCH_FLOAT_SAMPLES
+    // scale coefficients already here if using floating samples
+    const double scale = ::pow(0.5, (int)resultDivFactor);;
+#else
+    const short scale = 1;
+#endif
+
     for (uint i = 0; i < length; i ++)
     {
         filterCoeffs[i] = (SAMPLETYPE)(coeffs[i] * scale);
diff --git a/source/SoundTouch/FIRFilter.h b/source/SoundTouch/FIRFilter.h
index 0acb199..0ae5083 100644
--- a/source/SoundTouch/FIRFilter.h
+++ b/source/SoundTouch/FIRFilter.h
@@ -52,9 +52,6 @@ protected:
     // Result divider factor in 2^k format
     uint resultDivFactor;
 
-    // Result divider value.
-    SAMPLETYPE resultDivider;
-
     // Memory for filter coefficients
     SAMPLETYPE *filterCoeffs;
     SAMPLETYPE *filterCoeffsStereo;
diff --git a/source/SoundTouch/sse_optimized.cpp b/source/SoundTouch/sse_optimized.cpp
index 73658a5..f3511bc 100644
--- a/source/SoundTouch/sse_optimized.cpp
+++ b/source/SoundTouch/sse_optimized.cpp
@@ -211,9 +211,6 @@ FIRFilterSSE::~FIRFilterSSE()
 // (overloaded) Calculates filter coefficients for SSE routine
 void FIRFilterSSE::setCoefficients(const float *coeffs, uint newLength, uint uResultDivFactor)
 {
-    uint i;
-    float fDivider;
-
     FIRFilter::setCoefficients(coeffs, newLength, uResultDivFactor);
 
     // Scale the filter coefficients so that it won't be necessary to scale the filtering result
@@ -223,13 +220,13 @@ void FIRFilterSSE::setCoefficients(const float *coeffs, uint newLength, uint uRe
     filterCoeffsUnalign = new float[2 * newLength + 4];
     filterCoeffsAlign = (float *)SOUNDTOUCH_ALIGN_POINTER_16(filterCoeffsUnalign);
 
-    fDivider = (float)resultDivider;
+    const float scale = ::pow(0.5, (int)resultDivFactor);
 
-    // rearrange the filter coefficients for mmx routines
-    for (i = 0; i < newLength; i ++)
+    // rearrange the filter coefficients for sse routines
+    for (auto i = 0U; i < newLength; i ++)
     {
         filterCoeffsAlign[2 * i + 0] =
-        filterCoeffsAlign[2 * i + 1] = coeffs[i + 0] / fDivider;
+        filterCoeffsAlign[2 * i + 1] = coeffs[i] * scale;
     }
 }