Don't use a ringbuffer design for the limiter's side chain

Rather than continuously wrapping when used, each update uses it from the front
and copies the tail to the front at the end. This allows for more effficient
accesses in loops.

2 files changed, 37 insertions, 39 deletions

diff --git a/Alc/mastering.c b/Alc/mastering.c
index 306f0941..285f2f6d 100644
--- a/Alc/mastering.c
+++ b/Alc/mastering.c
@@ -73,8 +73,7 @@ static void ShiftSlidingHold(SlidingHold *Hold, const ALsizei n)
  */
 static void LinkChannels(Compressor *Comp, const ALsizei SamplesToDo, ALfloat (*restrict OutBuffer)[BUFFERSIZE])
 {
-    const ALsizei mask = 2*BUFFERSIZE - 1;
-    const ALsizei index = Comp->SideChainIndex + Comp->LookAhead;
+    const ALsizei index = Comp->LookAhead;
     const ALsizei numChans = Comp->NumChans;
     ALfloat *restrict sideChain = Comp->SideChain;
     ALsizei c, i;
@@ -83,15 +82,15 @@ static void LinkChannels(Compressor *Comp, const ALsizei SamplesToDo, ALfloat (*
     ASSUME(numChans > 0);
 
     for(i = 0;i < SamplesToDo;i++)
-        sideChain[(index + i) & mask] = 0.0f;
+        sideChain[index + i] = 0.0f;
 
     for(c = 0;c < numChans;c++)
     {
+        ALsizei offset = index;
         for(i = 0;i < SamplesToDo;i++)
         {
-            ALsizei offset = (index + i) & mask;
-
             sideChain[offset] = maxf(sideChain[offset], fabsf(OutBuffer[c][i]));
+            ++offset;
         }
     }
 }
@@ -103,9 +102,8 @@ static void LinkChannels(Compressor *Comp, const ALsizei SamplesToDo, ALfloat (*
  */
 static void CrestDetector(Compressor *Comp, const ALsizei SamplesToDo)
 {
-    const ALsizei mask = 2*BUFFERSIZE - 1;
     const ALfloat a_crest = Comp->CrestCoeff;
-    const ALsizei index = Comp->SideChainIndex + Comp->LookAhead;
+    const ALsizei index = Comp->LookAhead;
     const ALfloat *restrict sideChain = Comp->SideChain;
     ALfloat *restrict crestFactor = Comp->CrestFactor;
     ALfloat y2_peak = Comp->LastPeakSq;
@@ -116,7 +114,7 @@ static void CrestDetector(Compressor *Comp, const ALsizei SamplesToDo)
 
     for(i = 0;i < SamplesToDo;i++)
     {
-        ALfloat x_abs = sideChain[(index + i) & mask];
+        ALfloat x_abs = sideChain[index + i];
         ALfloat x2 = maxf(0.000001f, x_abs * x_abs);
 
         y2_peak = maxf(x2, lerp(x2, y2_peak, a_crest));
@@ -134,8 +132,7 @@ static void CrestDetector(Compressor *Comp, const ALsizei SamplesToDo)
  */
 static void PeakDetector(Compressor *Comp, const ALsizei SamplesToDo)
 {
-    const ALsizei mask = 2*BUFFERSIZE - 1;
-    const ALsizei index = Comp->SideChainIndex + Comp->LookAhead;
+    const ALsizei index = Comp->LookAhead;
     ALfloat *restrict sideChain = Comp->SideChain;
     ALsizei i;
 
@@ -143,8 +140,8 @@ static void PeakDetector(Compressor *Comp, const ALsizei SamplesToDo)
 
     for(i = 0;i < SamplesToDo;i++)
     {
-        ALuint offset = (index + i) & mask;
-        ALfloat x_abs = sideChain[offset];
+        const ALuint offset = index + i;
+        const ALfloat x_abs = sideChain[offset];
 
         sideChain[offset] = logf(maxf(0.000001f, x_abs));
     }
@@ -156,8 +153,7 @@ static void PeakDetector(Compressor *Comp, const ALsizei SamplesToDo)
  */
 static void PeakHoldDetector(Compressor *Comp, const ALsizei SamplesToDo)
 {
-    const ALsizei mask = 2*BUFFERSIZE - 1;
-    const ALsizei index = Comp->SideChainIndex + Comp->LookAhead;
+    const ALsizei index = Comp->LookAhead;
     ALfloat *restrict sideChain = Comp->SideChain;
     SlidingHold *hold = Comp->Hold;
     ALsizei i;
@@ -166,9 +162,9 @@ static void PeakHoldDetector(Compressor *Comp, const ALsizei SamplesToDo)
 
     for(i = 0;i < SamplesToDo;i++)
     {
-        ALsizei offset = (index + i) & mask;
-        ALfloat x_abs = sideChain[offset];
-        ALfloat x_G = logf(maxf(0.000001f, x_abs));
+        const ALsizei offset = index + i;
+        const ALfloat x_abs = sideChain[offset];
+        const ALfloat x_G = logf(maxf(0.000001f, x_abs));
 
         sideChain[offset] = UpdateSlidingHold(hold, i, x_G);
     }
@@ -183,7 +179,6 @@ static void PeakHoldDetector(Compressor *Comp, const ALsizei SamplesToDo)
  */
 static void GainCompressor(Compressor *Comp, const ALsizei SamplesToDo)
 {
-    const ALsizei mask = 2*BUFFERSIZE - 1;
     const bool autoKnee = Comp->Auto.Knee;
     const bool autoAttack = Comp->Auto.Attack;
     const bool autoRelease = Comp->Auto.Release;
@@ -194,7 +189,6 @@ static void GainCompressor(Compressor *Comp, const ALsizei SamplesToDo)
     const ALfloat slope = Comp->Slope;
     const ALfloat attack = Comp->Attack;
     const ALfloat release = Comp->Release;
-    const ALsizei index = Comp->SideChainIndex;
     const ALfloat c_est = Comp->GainEstimate;
     const ALfloat a_adp = Comp->AdaptCoeff;
     const ALfloat *restrict crestFactor = Comp->CrestFactor;
@@ -215,8 +209,8 @@ static void GainCompressor(Compressor *Comp, const ALsizei SamplesToDo)
     for(i = 0;i < SamplesToDo;i++)
     {
         const ALfloat y2_crest = crestFactor[i];
-        ALfloat x_G = sideChain[(index + lookAhead + i) & mask];
-        ALfloat x_over = x_G - threshold;
+        const ALfloat x_G = sideChain[lookAhead + i];
+        const ALfloat x_over = x_G - threshold;
         ALfloat knee_h;
         ALfloat y_G;
         ALfloat x_L;
@@ -272,15 +266,12 @@ static void GainCompressor(Compressor *Comp, const ALsizei SamplesToDo)
              * at the same output level.
              */
             if(autoDeclip)
-            {
-                x_G = sideChain[(index + i) & mask];
-                c_dev = maxf(c_dev, x_G - y_L - threshold - c_est);
-            }
+                c_dev = maxf(c_dev, sideChain[i] - y_L - threshold - c_est);
 
             postGain = -(c_dev + c_est);
         }
 
-        sideChain[(index + i) & mask] = expf(postGain - y_L);
+        sideChain[i] = expf(postGain - y_L);
     }
 
     Comp->LastRelease = y_1;
@@ -417,11 +408,9 @@ Compressor* CompressorInit(const ALuint NumChans, const ALuint SampleRate,
 
 void ApplyCompression(Compressor *Comp, const ALsizei SamplesToDo, ALfloat (*restrict OutBuffer)[BUFFERSIZE])
 {
-    const ALsizei mask = 2*BUFFERSIZE - 1;
     const ALsizei numChans = Comp->NumChans;
     const ALfloat preGain = Comp->PreGain;
-    const ALsizei index = Comp->SideChainIndex;
-    ALfloat *restrict sideChain = Comp->SideChain;
+    ALfloat *restrict sideChain;
     ALsizei c, i;
 
     ASSUME(SamplesToDo > 0);
@@ -451,11 +440,12 @@ void ApplyCompression(Compressor *Comp, const ALsizei SamplesToDo, ALfloat (*res
     if(Comp->Delay)
         SignalDelay(Comp, SamplesToDo, OutBuffer);
 
+    sideChain = Comp->SideChain;
     for(c = 0;c < numChans;c++)
     {
         for(i = 0;i < SamplesToDo;i++)
-            OutBuffer[c][i] *= sideChain[(index + i) & mask];
+            OutBuffer[c][i] *= sideChain[i];
     }
 
-    Comp->SideChainIndex = (index + SamplesToDo) & mask;
+    memmove(sideChain, sideChain+SamplesToDo, Comp->LookAhead*sizeof(ALfloat));
 }
diff --git a/Alc/mastering.h b/Alc/mastering.h
index 206a6c91..67738543 100644
--- a/Alc/mastering.h
+++ b/Alc/mastering.h
@@ -30,30 +30,38 @@ typedef struct SlidingHold
 typedef struct Compressor {
     ALsizei NumChans;
     ALuint SampleRate;
+
     struct {
-        ALuint Knee:1;
-        ALuint Attack:1;
-        ALuint Release:1;
-        ALuint PostGain:1;
-        ALuint Declip:1;
+        ALuint Knee : 1;
+        ALuint Attack : 1;
+        ALuint Release : 1;
+        ALuint PostGain : 1;
+        ALuint Declip : 1;
     } Auto;
+
     ALsizei LookAhead;
+
     ALfloat PreGain;
     ALfloat PostGain;
+
     ALfloat Threshold;
     ALfloat Slope;
     ALfloat Knee;
+
     ALfloat Attack;
     ALfloat Release;
-    ALfloat SideChain[2*BUFFERSIZE];
-    ALsizei SideChainIndex;
-    ALfloat CrestFactor[BUFFERSIZE];
+
+    alignas(16) ALfloat SideChain[2*BUFFERSIZE];
+    alignas(16) ALfloat CrestFactor[BUFFERSIZE];
+
     SlidingHold *Hold;
     ALfloat (*Delay)[BUFFERSIZE];
     ALsizei DelayIndex;
+
     ALfloat CrestCoeff;
     ALfloat GainEstimate;
     ALfloat AdaptCoeff;
+
     ALfloat LastPeakSq;
     ALfloat LastRmsSq;
     ALfloat LastRelease;