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Speed up group minimum and group output calculations for EXP_D25 and EXP_D45

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in encode_exponents_blk_ch() by removing the inner loops. This is about 30-40%
faster for the modified sections.

Originally committed as revision 26036 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Justin Ruggles 2010-12-16 21:09:16 +00:00
parent cdedf7e625
commit 834550ea0d
1 changed files with 37 additions and 19 deletions
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52
libavcodec/ac3enc.c
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@ -610,25 +610,36 @@ static void encode_exponents_blk_ch(uint8_t *exp,
int nb_exps, int exp_strategy,
uint8_t *num_exp_groups)
{
int group_size, nb_groups, i, j, k, exp_min;
int group_size, nb_groups, i, k;
group_size = exp_strategy + (exp_strategy == EXP_D45);
*num_exp_groups = (nb_exps + (group_size * 3) - 4) / (3 * group_size);
nb_groups = *num_exp_groups * 3;
/* for each group, compute the minimum exponent */
if (exp_strategy > EXP_D15) {
k = 1;
for (i = 1; i <= nb_groups; i++) {
exp_min = exp[k];
assert(exp_min >= 0 && exp_min <= 24);
for (j = 1; j < group_size; j++) {
if (exp[k+j] < exp_min)
exp_min = exp[k+j];
}
switch(exp_strategy) {
case EXP_D25:
for (i = 1, k = 1; i <= nb_groups; i++) {
uint8_t exp_min = exp[k];
if (exp[k+1] < exp_min)
exp_min = exp[k+1];
exp[i] = exp_min;
k += group_size;
k += 2;
}
break;
case EXP_D45:
for (i = 1, k = 1; i <= nb_groups; i++) {
uint8_t exp_min = exp[k];
if (exp[k+1] < exp_min)
exp_min = exp[k+1];
if (exp[k+2] < exp_min)
exp_min = exp[k+2];
if (exp[k+3] < exp_min)
exp_min = exp[k+3];
exp[i] = exp_min;
k += 4;
}
break;
}
/* constraint for DC exponent */
@ -644,13 +655,20 @@ static void encode_exponents_blk_ch(uint8_t *exp,
exp[i] = FFMIN(exp[i], exp[i+1] + 2);
/* now we have the exponent values the decoder will see */
if (exp_strategy > EXP_D15) {
k = nb_groups * group_size;
for (i = nb_groups; i > 0; i--) {
for (j = 0; j < group_size; j++)
exp[k-j] = exp[i];
k -= group_size;
switch (exp_strategy) {
case EXP_D25:
for (i = nb_groups, k = nb_groups * 2; i > 0; i--) {
uint8_t exp1 = exp[i];
exp[k--] = exp1;
exp[k--] = exp1;
}
break;
case EXP_D45:
for (i = nb_groups, k = nb_groups * 4; i > 0; i--) {
exp[k] = exp[k-1] = exp[k-2] = exp[k-3] = exp[i];
k -= 4;
}
break;
}
}