[FFmpeg-devel] [RFC] ac3dec: use dsputil.clear_block

[Reimar Döffinger]

Hello,
this gives an overall speedup of about 1.1 % on Intel Atom with my sample.
Testing with other CPUs and samples heavily welcome, I suspect a slowdown may 
be possible, beside it being a bit ugly.
Index: libavcodec/ac3dec.c
===================================================================
--- libavcodec/ac3dec.c	(revision 21191)
+++ libavcodec/ac3dec.c	(working copy)
@@ -565,6 +566,7 @@
  */
 static void decode_transform_coeffs(AC3DecodeContext *s, int blk)
 {
+    const int clearsize = 64 * sizeof(DCTELEM) / sizeof(s->fixed_coeffs[0][0]);
     int ch, end;
     int got_cplchan = 0;
     mant_groups m;
@@ -586,9 +588,12 @@
         } else {
             end = s->end_freq[ch];
         }
-        do
-            s->fixed_coeffs[ch][end] = 0;
-        while(++end < 256);
+        while (end & (clearsize - 1))
+            s->fixed_coeffs[ch][end++] = 0;
+        while (end < 256) {
+            s->dsp.clear_block((DCTELEM *)s->fixed_coeffs[ch] + end);
+            end += clearsize;
+        }
     }
 
     /* zero the dithered coefficients for appropriate channels */