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Use local variables outside the inner loop in extract_exponents() to reduce

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accessing of structs and arrays inside the loop.
Approx. 30% faster in function extract_exponents().

Originally committed as revision 26226 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Justin Ruggles 2011-01-05 16:02:08 +00:00
parent 5d3d238f82
commit 9be52d48d9
1 changed files with 7 additions and 4 deletions
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11
libavcodec/ac3enc.c
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@ -285,19 +285,22 @@ static void extract_exponents(AC3EncodeContext *s)
for (ch = 0; ch < s->channels; ch++) { for (ch = 0; ch < s->channels; ch++) {
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) { for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
AC3Block *block = &s->blocks[blk]; AC3Block *block = &s->blocks[blk];
uint8_t *exp = block->exp[ch];
CoefType *coef = block->mdct_coef[ch];
int exp_shift = block->exp_shift[ch];
for (i = 0; i < AC3_MAX_COEFS; i++) { for (i = 0; i < AC3_MAX_COEFS; i++) {
int e; int e;
int v = abs(SCALE_COEF(block->mdct_coef[ch][i])); int v = abs(SCALE_COEF(coef[i]));
if (v == 0) if (v == 0)
e = 24; e = 24;
else { else {
e = 23 - av_log2(v) + block->exp_shift[ch]; e = 23 - av_log2(v) + exp_shift;
if (e >= 24) { if (e >= 24) {
e = 24; e = 24;
block->mdct_coef[ch][i] = 0; coef[i] = 0;
} }
} }
block->exp[ch][i] = e; exp[i] = e;
} }
} }
} }