zynaddsubfx

commit 06f7a78ec194db4b0057776fee4e79246139e750
parent 581d320d4e044b0423728002393d8df411d33de1
Author: fundamental <mark.d.mccurry@gmail.com>
Date:   Wed, 10 Aug 2011 09:25:23 -0400

SUBnote: performance tweaking

- Manually unrolled inner filter loop for ~10% increase in throughput
- This section of code has tended to be a fairly large hotspot, so even
  micro optimizations here could yield visible performance gains.
- Another possible upgrade to this is making use of a lattice allpass structure
  for the band pass as described in Sanjit Mitra's DSP text.
- This could yield ~10% more throughput overall from simple tests and it should
  allow for much more trivial coefficient generation.

Diffstat:
M
src/Synth/SUBnote.cpp
 | 
32
++++++++++++++++++++++----------
M
src/Synth/SUBnote.h
 | 
1
+

2 files changed, 23 insertions(+), 10 deletions(-)
diff --git a/src/Synth/SUBnote.cpp b/src/Synth/SUBnote.cpp
@@ -23,6 +23,7 @@
 #include <cmath>
 #include <cstdlib>
 #include <cstdio>
+#include <cassert>
 #include "../globals.h"
 #include "SUBnote.h"
 #include "../Misc/Util.h"
@@ -313,18 +314,29 @@ void SUBnote::initfilter(bpfilter &filter,
 /*
  * Do the filtering
  */
+inline float SUBnote::SubFilter(bpfilter &filter, const float input) const
+{
+    const float out = input * filter.b0 + filter.b2 * filter.xn2
+                      - filter.a1 * filter.yn1 - filter.a2 * filter.yn2;
+    filter.xn2 = filter.xn1;
+    filter.xn1 = input;
+    filter.yn2 = filter.yn1;
+    filter.yn1 = out;
+    return out;
+}
+
 void SUBnote::filter(bpfilter &filter, float *smps)
 {
-    int      i;
-    float out;
-    for(i = 0; i < SOUND_BUFFER_SIZE; i++) {
-        out = smps[i] * filter.b0 + filter.b2 * filter.xn2
-              - filter.a1 * filter.yn1 - filter.a2 * filter.yn2;
-        filter.xn2 = filter.xn1;
-        filter.xn1 = smps[i];
-        filter.yn2 = filter.yn1;
-        filter.yn1 = out;
-        smps[i]    = out;
+    assert(SOUND_BUFFER_SIZE % 8 == 0);
+    for(int i = 0; i < SOUND_BUFFER_SIZE; i += 8) {
+        smps[i] =   SubFilter(filter, smps[i]);
+        smps[i+1] = SubFilter(filter, smps[i+1]);
+        smps[i+2] = SubFilter(filter, smps[i+2]);
+        smps[i+3] = SubFilter(filter, smps[i+3]);
+        smps[i+4] = SubFilter(filter, smps[i+4]);
+        smps[i+5] = SubFilter(filter, smps[i+5]);
+        smps[i+6] = SubFilter(filter, smps[i+6]);
+        smps[i+7] = SubFilter(filter, smps[i+7]);
     }
 }
 
diff --git a/src/Synth/SUBnote.h b/src/Synth/SUBnote.h
@@ -91,6 +91,7 @@ class SUBnote :public SynthNote
                                 float freq,
                                 float bw,
                                 float gain);
+        inline float SubFilter(bpfilter &filter, float input) const;
         inline void filter(bpfilter &filter, float *smps);
 
         bpfilter *lfilter, *rfilter;