[Ffmpeg-devel] Re: [Ffmpeg-cvslog] r7570 - trunk/libavutil/fifo.c

[Michael Niedermayer]

Hi

On Thu, Jan 18, 2007 at 04:41:21PM -0800, Roman Shaposhnik wrote:
[...]
> 
> > the extra if() also should disapear for av_fifo_read() if its inlined
> > and the body of the while loop will be executed just once normally
> > and rarely twice, but never more often then twice
> > 
> > do you know of any specific places in libav* where there are so many
> > calls to av_fifo_*read() that this could matter?
> 
>   Nope. All I care about is av_fifo_peek() ;-)

attached patch removes it and makes your code about 35% faster ;)

and i suspect it can be made even faster, of course this is not possible
with a av_fifo_peek like system

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

There will always be a question for which you do not know the correct awnser.
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Index: libavformat/dvenc.c
===================================================================
--- libavformat/dvenc.c	(revision 7537)
+++ libavformat/dvenc.c	(working copy)
@@ -177,21 +177,33 @@
 
 static void dv_inject_audio(DVMuxContext *c, int channel, uint8_t* frame_ptr)
 {
-    int i, j, d, of, size;
+    int i, j, d, size;
+    uint8_t *fifo_ptr, *fifo_end;
+    AVFifoBuffer *f= &c->audio_data[channel];
     size = 4 * dv_audio_frame_size(c->sys, c->frames);
     frame_ptr += channel * c->sys->difseg_size * 150 * 80;
     for (i = 0; i < c->sys->difseg_size; i++) {
        frame_ptr += 6 * 80; /* skip DIF segment header */
        for (j = 0; j < 9; j++) {
           dv_write_pack(dv_aaux_packs_dist[i][j], c, &frame_ptr[3], i >= c->sys->difseg_size/2);
-          for (d = 8; d < 80; d+=2) {
-             of = c->sys->audio_shuffle[i][j] + (d - 8)/2 * c->sys->audio_stride;
-             if (of*2 >= size)
-                 continue;
+          fifo_ptr  = f->rptr + 2*c->sys->audio_shuffle[i][j];
+          fifo_end  = FFMIN(f->end, f->rptr + size);
+          for (d = 8; d < 80; d+=2, fifo_ptr += 2*c->sys->audio_stride) {
+             if (fifo_ptr >= fifo_end)
+                 break;
 
-             frame_ptr[d] = av_fifo_peek(&c->audio_data[channel], of*2+1); // FIXME: may be we have to admit
-             frame_ptr[d+1] = av_fifo_peek(&c->audio_data[channel], of*2); //        that DV is a big endian PCM
+             frame_ptr[d  ] = fifo_ptr[1];// FIXME: may be we have to admit that DV is a big endian PCM
+             frame_ptr[d+1] = fifo_ptr[0];
           }
+          fifo_ptr -= f->end - f->buffer;
+          fifo_end = f->rptr + size - f->end + f->buffer;
+          for (; d < 80; d+=2, fifo_ptr += 2*c->sys->audio_stride) {
+             if (fifo_ptr >= fifo_end)
+                 break;
+
+             frame_ptr[d  ] = fifo_ptr[1];// FIXME: may be we have to admit that DV is a big endian PCM
+             frame_ptr[d+1] = fifo_ptr[0];
+          }
           frame_ptr += 16 * 80; /* 15 Video DIFs + 1 Audio DIF */
        }
     }
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