From 08965b22e2565dffc2aaadf25ec8a481eadf6285 Mon Sep 17 00:00:00 2001 From: Loren Merritt Date: Sun, 30 Sep 2007 02:12:03 +0000 Subject: [PATCH] replace FIR with finite differences. 3x faster decode_subframe_fixed(). overall flac decoding: 10% faster if file was encoded with fixed predictors. Originally committed as revision 10626 to svn://svn.ffmpeg.org/ffmpeg/trunk --- libavcodec/flac.c | 33 +++++++++++++++++---------------- 1 file changed, 17 insertions(+), 16 deletions(-) diff --git a/libavcodec/flac.c b/libavcodec/flac.c index d8e8813d9e..5c0a2f76b1 100644 --- a/libavcodec/flac.c +++ b/libavcodec/flac.c @@ -259,7 +259,9 @@ static int decode_residuals(FLACContext *s, int channel, int pred_order) static int decode_subframe_fixed(FLACContext *s, int channel, int pred_order) { - int i; + const int blocksize = s->blocksize; + int32_t *decoded = s->decoded[channel]; + int a, b, c, d, i; // av_log(s->avctx, AV_LOG_DEBUG, " SUBFRAME FIXED\n"); @@ -268,38 +270,37 @@ static int decode_subframe_fixed(FLACContext *s, int channel, int pred_order) for (i = 0; i < pred_order; i++) { - s->decoded[channel][i] = get_sbits(&s->gb, s->curr_bps); + decoded[i] = get_sbits(&s->gb, s->curr_bps); // av_log(s->avctx, AV_LOG_DEBUG, " %d: %d\n", i, s->decoded[channel][i]); } if (decode_residuals(s, channel, pred_order) < 0) return -1; + a = decoded[pred_order-1]; + b = a - decoded[pred_order-2]; + c = b - decoded[pred_order-2] + decoded[pred_order-3]; + d = c - decoded[pred_order-2] + 2*decoded[pred_order-3] - decoded[pred_order-4]; + switch(pred_order) { case 0: break; case 1: - for (i = pred_order; i < s->blocksize; i++) - s->decoded[channel][i] += s->decoded[channel][i-1]; + for (i = pred_order; i < blocksize; i++) + decoded[i] = a += decoded[i]; break; case 2: - for (i = pred_order; i < s->blocksize; i++) - s->decoded[channel][i] += 2*s->decoded[channel][i-1] - - s->decoded[channel][i-2]; + for (i = pred_order; i < blocksize; i++) + decoded[i] = a += b += decoded[i]; break; case 3: - for (i = pred_order; i < s->blocksize; i++) - s->decoded[channel][i] += 3*s->decoded[channel][i-1] - - 3*s->decoded[channel][i-2] - + s->decoded[channel][i-3]; + for (i = pred_order; i < blocksize; i++) + decoded[i] = a += b += c += decoded[i]; break; case 4: - for (i = pred_order; i < s->blocksize; i++) - s->decoded[channel][i] += 4*s->decoded[channel][i-1] - - 6*s->decoded[channel][i-2] - + 4*s->decoded[channel][i-3] - - s->decoded[channel][i-4]; + for (i = pred_order; i < blocksize; i++) + decoded[i] = a += b += c += d += decoded[i]; break; default: av_log(s->avctx, AV_LOG_ERROR, "illegal pred order %d\n", pred_order);