From bf1cf4d5a5c73942b193ccf4af75dd851f4f4fd2 Mon Sep 17 00:00:00 2001 From: Mans Rullgard Date: Thu, 5 Jul 2012 12:25:40 +0100 Subject: flacdec: reverse lpc coeff order, simplify filter Reversing the lpc coefficient order simplifies indexing in the filter. Signed-off-by: Mans Rullgard --- libavcodec/flacdsp.c | 27 +++++++++++++-------------- 1 file changed, 13 insertions(+), 14 deletions(-) (limited to 'libavcodec/flacdsp.c') diff --git a/libavcodec/flacdsp.c b/libavcodec/flacdsp.c index a2e335b4de..88d689d3eb 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; } } -- cgit v1.2.3