Reversing the lpc coefficient order simplifies indexing in
the filter.
Signed-off-by: Mans Rullgard <[email protected]>
---
libavcodec/flacdec.c | 2 +-
libavcodec/flacdsp.c | 27 +++++++++++++--------------
2 files changed, 14 insertions(+), 15 deletions(-)
diff --git a/libavcodec/flacdec.c b/libavcodec/flacdec.c
index 53070a3..8cbd389 100644
--- a/libavcodec/flacdec.c
+++ b/libavcodec/flacdec.c
@@ -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)
diff --git a/libavcodec/flacdsp.c b/libavcodec/flacdsp.c
index a2e335b..88d689d 100644
--- a/libavcodec/flacdsp.c
+++ b/libavcodec/flacdsp.c
@@ -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;
}
}
--
1.7.11.1
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