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flacdec: reverse lpc coeff order, simplify filter 

Reversing the lpc coefficient order simplifies indexing in
the filter.

Signed-off-by: Mans Rullgard <mans@mansr.com>
This commit is contained in:
Mans Rullgard 2012-07-05 12:25:40 +01:00
parent 9f97af2688
commit bf1cf4d5a5
2 changed files with 14 additions and 15 deletions
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2
libavcodec/flacdec.c
View File

@ -321,7 +321,7 @@ static int decode_subframe_lpc(FLACContext *s, int channel, int pred_order,
}
for (i = 0; i < pred_order; i++) {
coeffs[i] = get_sbits(&s->gb, coeff_prec);
coeffs[pred_order - i - 1] = get_sbits(&s->gb, coeff_prec);
}
if (decode_residuals(s, channel, pred_order) < 0)

27
libavcodec/flacdsp.c
View File

@ -45,27 +45,26 @@ static void flac_lpc_16_c(int32_t *decoded, const int coeffs[32],
{
int i, j;
for (i = pred_order; i < len - 1; i += 2) {
int c;
int d = decoded[i-pred_order];
for (i = pred_order; i < len - 1; i += 2, decoded += 2) {
int c = coeffs[0];
int d = decoded[0];
int s0 = 0, s1 = 0;
for (j = pred_order-1; j > 0; j--) {
c = coeffs[j];
for (j = 1; j < pred_order; j++) {
s0 += c*d;
d = decoded[i-j];
d = decoded[j];
s1 += c*d;
c = coeffs[j];
}
c = coeffs[0];
s0 += c*d;
d = decoded[i] += s0 >> qlevel;
d = decoded[j] += s0 >> qlevel;
s1 += c*d;
decoded[i+1] += s1 >> qlevel;
decoded[j + 1] += s1 >> qlevel;
}
if (i < len) {
int sum = 0;
for (j = 0; j < pred_order; j++)
sum += coeffs[j] * decoded[i-j-1];
decoded[i] += sum >> qlevel;
sum += coeffs[j] * decoded[j];
decoded[j] += sum >> qlevel;
}
}
@ -74,11 +73,11 @@ static void flac_lpc_32_c(int32_t *decoded, const int coeffs[32],
{
int i, j;
for (i = pred_order; i < len; i++) {
for (i = pred_order; i < len; i++, decoded++) {
int64_t sum = 0;
for (j = 0; j < pred_order; j++)
sum += (int64_t)coeffs[j] * decoded[i-j-1];
decoded[i] += sum >> qlevel;
sum += (int64_t)coeffs[j] * decoded[j];
decoded[j] += sum >> qlevel;
}
}