zynaddsubfx

commit 1778cb7c174d135d533e3fa8cdf27778380faff9
parent b1d12c22154b517a1c347c385b2e5c2fd8d8c195
Author: fundamental <mark.d.mccurry@gmail.com>
Date:   Sat, 17 Aug 2013 17:06:08 -0400

SUBnote: 2x Speed Enhancement

Well, SUBnote is now a LOT faster. According to the SUBnoteTest
the time to compute samples is about halved now due to a change
in the filtering code.
Time for 15,000 samples went from 2.75 sec to 1.34 sec under
the BuildOptionsBasic configuration.
This should reflect real usage as both cases were compute bound
in the filtering loop.

Diffstat:
M
src/Synth/SUBnote.cpp
 | 
45
+++++++++++++++++++++++++++++----------------
M
src/Synth/SUBnote.h
 | 
1
-

2 files changed, 29 insertions(+), 17 deletions(-)
diff --git a/src/Synth/SUBnote.cpp b/src/Synth/SUBnote.cpp
@@ -322,30 +322,43 @@ void SUBnote::initfilter(bpfilter &filter,
 /*
  * Do the filtering
  */
-inline float SUBnote::SubFilter(bpfilter &filter, const float input) const
+
+inline void SubFilterA(const float coeff[4], float &src, float work[4])
 {
-    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;
+    work[3] = src*coeff[0]+work[1]*coeff[1]+work[2]*coeff[2]+work[3]*coeff[3];
+    work[1] = src;
+    src     = work[3];
 }
 
+inline void SubFilterB(const float coeff[4], float &src, float work[4])
+{
+    work[2] = src*coeff[0]+work[0]*coeff[1]+work[3]*coeff[2]+work[2]*coeff[3];
+    work[0] = src;
+    src     = work[2];
+}
+
+//This dance is designed to minimize unneeded memory operations which can result
+//in quite a bit of wasted time
 void SUBnote::filter(bpfilter &filter, float *smps)
 {
     assert(synth->buffersize % 8 == 0);
+    float coeff[4] = {filter.b0, filter.b2,  -filter.a1, -filter.a2};
+    float work[4]  = {filter.xn1, filter.xn2, filter.yn1, filter.yn2};
+
     for(int i = 0; i < synth->buffersize; 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]);
+        SubFilterA(coeff, smps[i + 0], work);
+        SubFilterB(coeff, smps[i + 1], work);
+        SubFilterA(coeff, smps[i + 2], work);
+        SubFilterB(coeff, smps[i + 3], work);
+        SubFilterA(coeff, smps[i + 4], work);
+        SubFilterB(coeff, smps[i + 5], work);
+        SubFilterA(coeff, smps[i + 6], work);
+        SubFilterB(coeff, smps[i + 7], work);
     }
+    filter.xn1 = work[0];
+    filter.xn2 = work[1];
+    filter.yn1 = work[2];
+    filter.yn2 = work[3];
 }
 
 /*
diff --git a/src/Synth/SUBnote.h b/src/Synth/SUBnote.h
@@ -95,7 +95,6 @@ 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;