[SCM] libav/experimental: encode_residual_fixed(): replace FIR with finite differences. 4x faster order 2, 3.5x order 3, 3x order 4. overall flac encoding: 35% faster at compression_levels 0-2, no effect at higher levels.

[siretart at users.alioth.debian.org]

The following commit has been merged in the experimental branch:
commit a309dce75fb08f9c7b4a248afab97d5ac105b9b3
Author: Loren Merritt <lorenm at u.washington.edu>
Date:   Sat Sep 29 23:21:57 2007 +0000

    encode_residual_fixed(): replace FIR with finite differences.
    4x faster order 2, 3.5x order 3, 3x order 4.
    overall flac encoding: 35% faster at compression_levels 0-2, no effect at higher levels.
    
    Originally committed as revision 10624 to svn://svn.ffmpeg.org/ffmpeg/trunk

diff --git a/libavcodec/flacenc.c b/libavcodec/flacenc.c
index 5f9d78e..e2627a8 100644
--- a/libavcodec/flacenc.c
+++ b/libavcodec/flacenc.c
@@ -840,14 +840,35 @@ static void encode_residual_fixed(int32_t *res, const int32_t *smp, int n,
         for(i=order; i<n; i++)
             res[i]= smp[i] - smp[i-1];
     }else if(order==2){
-        for(i=order; i<n; i++)
-            res[i]= smp[i] - 2*smp[i-1] + smp[i-2];
+        int a = smp[order-1] - smp[order-2];
+        for(i=order; i<n; i++) {
+            int b = smp[i] - smp[i-1];
+            res[i]= b - a;
+            a = b;
+        }
     }else if(order==3){
-        for(i=order; i<n; i++)
-            res[i]= smp[i] - 3*smp[i-1] + 3*smp[i-2] - smp[i-3];
+        int a = smp[order-1] - smp[order-2];
+        int c = smp[order-1] - 2*smp[order-2] + smp[order-3];
+        for(i=order; i<n; i++) {
+            int b = smp[i] - smp[i-1];
+            int d = b - a;
+            res[i]= d - c;
+            a = b;
+            c = d;
+        }
     }else{
-        for(i=order; i<n; i++)
-            res[i]= smp[i] - 4*smp[i-1] + 6*smp[i-2] - 4*smp[i-3] + smp[i-4];
+        int a = smp[order-1] - smp[order-2];
+        int c = smp[order-1] - 2*smp[order-2] + smp[order-3];
+        int e = smp[order-1] - 3*smp[order-2] + 3*smp[order-3] - smp[order-4];
+        for(i=order; i<n; i++) {
+            int b = smp[i] - smp[i-1];
+            int d = b - a;
+            int f = d - c;
+            res[i]= f - e;
+            a = b;
+            c = d;
+            e = f;
+        }
     }
 }
 

-- 
Libav/FFmpeg packaging