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Optimize short-term prediction by reducing index arithmetic. 

Originally committed as revision 21069 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Thilo Borgmann 2010-01-07 22:23:28 +00:00
parent 9a02c3e183
commit 99c5f5ccbe
1 changed files with 19 additions and 6 deletions
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25
libavcodec/alsdec.c
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@ -712,6 +712,8 @@ static int decode_var_block_data(ALSDecContext *ctx, ALSBlockData *bd)
int32_t *quant_cof = bd->quant_cof;
int32_t *lpc_cof = bd->lpc_cof;
int32_t *raw_samples = bd->raw_samples;
int32_t *raw_samples_end = bd->raw_samples + bd->block_length;
int32_t lpc_cof_reversed[opt_order];
// reverse long-term prediction
if (*bd->use_ltp) {
@ -739,9 +741,9 @@ static int decode_var_block_data(ALSDecContext *ctx, ALSBlockData *bd)
y = 1 << 19;
for (sb = 0; sb < smp; sb++)
y += MUL64(lpc_cof[sb], *(raw_samples + smp - (sb + 1)));
y += MUL64(lpc_cof[sb], raw_samples[-(sb + 1)]);
raw_samples[smp] -= y >> 20;
*raw_samples++ -= y >> 20;
parcor_to_lpc(smp, quant_cof, lpc_cof);
}
} else {
@ -775,16 +777,27 @@ static int decode_var_block_data(ALSDecContext *ctx, ALSBlockData *bd)
raw_samples[sb] >>= bd->shift_lsbs;
}
// reverse linear prediction coefficients for efficiency
lpc_cof = lpc_cof + opt_order;
for (sb = 0; sb < opt_order; sb++)
lpc_cof_reversed[sb] = lpc_cof[-(sb + 1)];
// reconstruct raw samples
for (; smp < bd->block_length; smp++) {
raw_samples = bd->raw_samples + smp;
lpc_cof = lpc_cof_reversed + opt_order;
for (; raw_samples < raw_samples_end; raw_samples++) {
y = 1 << 19;
for (sb = 0; sb < opt_order; sb++)
y += MUL64(bd->lpc_cof[sb], *(raw_samples + smp - (sb + 1)));
for (sb = -opt_order; sb < 0; sb++)
y += MUL64(lpc_cof[sb], raw_samples[sb]);
raw_samples[smp] -= y >> 20;
*raw_samples -= y >> 20;
}
raw_samples = bd->raw_samples;
// restore previous samples in case that they have been altered
if (bd->store_prev_samples)
memcpy(raw_samples - sconf->max_order, bd->prev_raw_samples,