[SCM] libav/experimental: Small refactoring: Instead of 4 loops for decoding AC coefficients based on their grouping, create one loop that indexes into a table of AC VLC tables.
siretart at users.alioth.debian.org
siretart at users.alioth.debian.org
Sun Jun 30 16:55:20 UTC 2013
The following commit has been merged in the experimental branch:
commit 9d8bb0318a0bc59a04c71555a3c575f8146eab41
Author: Mike Melanson <mike at multimedia.cx>
Date: Wed Dec 2 04:06:27 2009 +0000
Small refactoring: Instead of 4 loops for decoding AC coefficients based
on their grouping, create one loop that indexes into a table of AC VLC
tables.
There is also a small optimization here: Do not call unpack_vlcs()
if there are no fragments in the list with outstanding coefficients.
My profiling indicates that this can save upwards of 1 million
dezicycles per frame throughout the course of unpack_dct_coeffs().
Originally committed as revision 20699 to svn://svn.ffmpeg.org/ffmpeg/trunk
diff --git a/libavcodec/vp3.c b/libavcodec/vp3.c
index 292f010..cdf8e00 100644
--- a/libavcodec/vp3.c
+++ b/libavcodec/vp3.c
@@ -1163,6 +1163,8 @@ static int unpack_dct_coeffs(Vp3DecodeContext *s, GetBitContext *gb)
int ac_y_table;
int ac_c_table;
int residual_eob_run = 0;
+ VLC *y_tables[64];
+ VLC *c_tables[64];
/* fetch the DC table indexes */
dc_y_table = get_bits(gb, 4);
@@ -1192,40 +1194,33 @@ static int unpack_dct_coeffs(Vp3DecodeContext *s, GetBitContext *gb)
ac_y_table = get_bits(gb, 4);
ac_c_table = get_bits(gb, 4);
- /* unpack the group 1 AC coefficients (coeffs 1-5) */
+ /* build tables of AC VLC tables */
for (i = 1; i <= 5; i++) {
- residual_eob_run = unpack_vlcs(s, gb, &s->ac_vlc_1[ac_y_table], i,
- 1, residual_eob_run);
-
- residual_eob_run = unpack_vlcs(s, gb, &s->ac_vlc_1[ac_c_table], i,
- 0, residual_eob_run);
+ y_tables[i] = &s->ac_vlc_1[ac_y_table];
+ c_tables[i] = &s->ac_vlc_1[ac_c_table];
}
-
- /* unpack the group 2 AC coefficients (coeffs 6-14) */
for (i = 6; i <= 14; i++) {
- residual_eob_run = unpack_vlcs(s, gb, &s->ac_vlc_2[ac_y_table], i,
- 1, residual_eob_run);
-
- residual_eob_run = unpack_vlcs(s, gb, &s->ac_vlc_2[ac_c_table], i,
- 0, residual_eob_run);
+ y_tables[i] = &s->ac_vlc_2[ac_y_table];
+ c_tables[i] = &s->ac_vlc_2[ac_c_table];
}
-
- /* unpack the group 3 AC coefficients (coeffs 15-27) */
for (i = 15; i <= 27; i++) {
- residual_eob_run = unpack_vlcs(s, gb, &s->ac_vlc_3[ac_y_table], i,
- 1, residual_eob_run);
-
- residual_eob_run = unpack_vlcs(s, gb, &s->ac_vlc_3[ac_c_table], i,
- 0, residual_eob_run);
+ y_tables[i] = &s->ac_vlc_3[ac_y_table];
+ c_tables[i] = &s->ac_vlc_3[ac_c_table];
}
-
- /* unpack the group 4 AC coefficients (coeffs 28-63) */
for (i = 28; i <= 63; i++) {
- residual_eob_run = unpack_vlcs(s, gb, &s->ac_vlc_4[ac_y_table], i,
- 1, residual_eob_run);
+ y_tables[i] = &s->ac_vlc_4[ac_y_table];
+ c_tables[i] = &s->ac_vlc_4[ac_c_table];
+ }
+
+ /* decode all AC coefficents */
+ for (i = 1; i <= 63; i++) {
+ if (s->fragment_list_y_head != -1)
+ residual_eob_run = unpack_vlcs(s, gb, y_tables[i], i,
+ 1, residual_eob_run);
- residual_eob_run = unpack_vlcs(s, gb, &s->ac_vlc_4[ac_c_table], i,
- 0, residual_eob_run);
+ if (s->fragment_list_c_head != -1)
+ residual_eob_run = unpack_vlcs(s, gb, c_tables[i], i,
+ 0, residual_eob_run);
}
return 0;
--
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