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Simplify run level decoding:

Browse Source 
- remove unneeded vlc code < 0 check
- reorder vlc code handling so that the unlikely escape decoding
  part comes last
- move overflow check out of the decode loop
- branchless sign conversion

Originally committed as revision 19234 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Sascha Sommer 2009-06-20 11:06:48 +00:00
parent 4d67e067e2
commit 4df8bdeef3
1 changed files with 21 additions and 30 deletions

51
libavcodec/wma.c
View File

@ -470,23 +470,24 @@ int ff_wma_run_level_decode(AVCodecContext* avctx, GetBitContext* gb,
int num_coefs, int block_len, int frame_len_bits,
int coef_nb_bits)
{
int code, run, level, sign;
WMACoef* eptr = ptr + num_coefs;
ptr += offset;
for(;;) {
int code, level, sign;
const unsigned int coef_mask = block_len - 1;
for (; offset < num_coefs; offset++) {
code = get_vlc2(gb, vlc->table, VLCBITS, VLCMAX);
if (code < 0)
return -1;
if (code == 1) {
if (code > 1) {
/** normal code */
offset += run_table[code];
level = level_table[code];
} else if (code == 1) {
/* EOB */
break;
} else if (code == 0) {
} else {
/* escape */
if (!version) {
level = get_bits(gb, coef_nb_bits);
/* NOTE: this is rather suboptimal. reading
block_len_bits would be better */
run = get_bits(gb, frame_len_bits);
offset += get_bits(gb, frame_len_bits);
} else {
level = ff_wma_get_large_val(gb);
/** escape decode */
@ -497,31 +498,21 @@ int ff_wma_run_level_decode(AVCodecContext* avctx, GetBitContext* gb,
"broken escape sequence\n");
return -1;
} else
run = get_bits(gb, frame_len_bits) + 4;
offset += get_bits(gb, frame_len_bits) + 4;
} else
run = get_bits(gb, 2) + 1;
} else
run = 0;
offset += get_bits(gb, 2) + 1;
}
}
} else {
/* normal code */
run = run_table[code];
level = level_table[code];
}
sign = get_bits1(gb);
if (!sign)
level = -level;
ptr += run;
if (ptr >= eptr)
{
av_log(NULL, AV_LOG_ERROR, "overflow in spectral RLE, ignoring\n");
break;
}
*ptr++ = level;
/* NOTE: EOB can be omitted */
if (ptr >= eptr)
break;
sign = get_bits1(gb) - 1;
ptr[offset & coef_mask] = (level^sign) - sign;
}
/** NOTE: EOB can be omitted */
if (offset > num_coefs) {
av_log(avctx, AV_LOG_ERROR, "overflow in spectral RLE, ignoring\n");
return -1;
}
return 0;
}