Hello all,
The attached patch provides quite a nice performance improvement (something
like 8% better overall when benchmarked on desktop PC).
Best regards,
Siarhei Siamashka
>From 8399813f77c45eda6aa356977294bed859b02c58 Mon Sep 17 00:00:00 2001
From: Siarhei Siamashka <siarhei.siamashka@xxxxxxxxx>
Date: Sun, 4 Jan 2009 03:11:12 +0200
Subject: [PATCH] Use of constant shift in SBC quantization code to make it faster
The result of 32x32->64 unsigned long multiplication is returned
in two registers (high and low 32-bit parts) for many 32-bit
architectures. For these architectures constant right shift by
32 bits is optimized out by the compiler to just taking the high
32-bit part. Also some data needed at the quantization stage is
precalculated beforehand to improve performance.
---
sbc/sbc.c | 23 +++++++++++++----------
1 files changed, 13 insertions(+), 10 deletions(-)
diff --git a/sbc/sbc.c b/sbc/sbc.c
index b349090..650bc2f 100644
--- a/sbc/sbc.c
+++ b/sbc/sbc.c
@@ -880,11 +880,12 @@ static int sbc_pack_frame(uint8_t *data, struct sbc_frame *frame, size_t len)
uint8_t crc_header[11] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
int crc_pos = 0;
- uint16_t audio_sample;
+ uint32_t audio_sample;
int ch, sb, blk; /* channel, subband, block and bit counters */
int bits[2][8]; /* bits distribution */
- int levels[2][8]; /* levels are derived from that */
+ uint32_t levels[2][8]; /* levels are derived from that */
+ uint32_t sb_sample_delta[2][8];
u_int32_t scalefactor[2][8]; /* derived from frame->scale_factor */
@@ -1017,8 +1018,14 @@ static int sbc_pack_frame(uint8_t *data, struct sbc_frame *frame, size_t len)
sbc_calculate_bits(frame, bits);
for (ch = 0; ch < frame->channels; ch++) {
- for (sb = 0; sb < frame->subbands; sb++)
- levels[ch][sb] = (1 << bits[ch][sb]) - 1;
+ for (sb = 0; sb < frame->subbands; sb++) {
+ levels[ch][sb] = ((1 << bits[ch][sb]) - 1) <<
+ (32 - (frame->scale_factor[ch][sb] +
+ SCALE_OUT_BITS + 2));
+ sb_sample_delta[ch][sb] = (uint32_t) 1 <<
+ (frame->scale_factor[ch][sb] +
+ SCALE_OUT_BITS + 1);
+ }
}
for (blk = 0; blk < frame->blocks; blk++) {
@@ -1029,12 +1036,8 @@ static int sbc_pack_frame(uint8_t *data, struct sbc_frame *frame, size_t len)
continue;
audio_sample = ((uint64_t) levels[ch][sb] *
- (((uint32_t) 1 <<
- (frame->scale_factor[ch][sb] +
- SCALE_OUT_BITS + 1)) +
- frame->sb_sample_f[blk][ch][sb])) >>
- (frame->scale_factor[ch][sb] +
- SCALE_OUT_BITS + 2);
+ (sb_sample_delta[ch][sb] +
+ frame->sb_sample_f[blk][ch][sb])) >> 32;
PUT_BITS(audio_sample, bits[ch][sb]);
}
--
1.5.6.5
