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Small refactoring: Instead of 4 loops for decoding AC coefficients based

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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
This commit is contained in:
Mike Melanson 2009-12-02 04:06:27 +00:00
parent 098523eb28
commit 9d8bb0318a
1 changed files with 21 additions and 26 deletions
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47
libavcodec/vp3.c
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@ -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];
}
for (i = 28; i <= 63; i++) {
y_tables[i] = &s->ac_vlc_4[ac_y_table];
c_tables[i] = &s->ac_vlc_4[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);
/* 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;