h264: Don't store intra pcm samples in h->mb

Instead, keep them in the bitstream buffer until we read them verbatim,
this saves a memcpy() and a subsequent clearing of the target buffer.
decode_cabac+decode_mb for a sample file (CAPM3_Sony_D.jsv) goes from
6121.4 to 6095.5 cycles, i.e. 26 cycles faster.

Signed-off-by: Martin Storsjö <martin@martin.st>

1 files changed, 3 insertions, 8 deletions

diff --git a/libavcodec/h264_cavlc.c b/libavcodec/h264_cavlc.c
index 9585b77830..4b44cbefa9 100644
--- a/libavcodec/h264_cavlc.c
+++ b/libavcodec/h264_cavlc.c
@@ -761,17 +761,12 @@ decode_intra_mb:
     h->slice_table[ mb_xy ]= h->slice_num;
 
     if(IS_INTRA_PCM(mb_type)){
-        unsigned int x;
         const int mb_size = ff_h264_mb_sizes[h->sps.chroma_format_idc] *
-                            h->sps.bit_depth_luma >> 3;
+                            h->sps.bit_depth_luma;
 
         // We assume these blocks are very rare so we do not optimize it.
-        align_get_bits(&h->gb);
-
-        // The pixels are stored in the same order as levels in h->mb array.
-        for(x=0; x < mb_size; x++){
-            ((uint8_t*)h->mb)[x]= get_bits(&h->gb, 8);
-        }
+        h->intra_pcm_ptr = align_get_bits(&h->gb);
+        skip_bits_long(&h->gb, mb_size);
 
         // In deblocking, the quantizer is 0
         h->cur_pic.f.qscale_table[mb_xy] = 0;