From 3d51be014c4e50b88985d3e6998438f15bdfc4a1 Mon Sep 17 00:00:00 2001
From: Alex Converse <alex.converse@gmail.com>
Date: Fri, 17 Jul 2009 14:21:49 +0000
Subject: [PATCH] Replace pow(x, 0.75) with sqrtf(x * sqrtf(x)) for a 33%
speedup.
Originally committed as revision 19459 to svn://svn.ffmpeg.org/ffmpeg/trunk
---
libavcodec/aaccoder.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/libavcodec/aaccoder.c b/libavcodec/aaccoder.c
index 41f7c208a83..3b6ec968765 100644
--- a/libavcodec/aaccoder.c
+++ b/libavcodec/aaccoder.c
@@ -61,7 +61,8 @@ static const uint8_t *run_value_bits[2] = {
*/
static av_always_inline int quant(float coef, const float Q)
{
- return pow(coef * Q, 0.75) + 0.4054;
+ float a = coef * Q;
+ return sqrtf(a * sqrtf(a)) + 0.4054;
}
static void quantize_bands(int (*out)[2], const float *in, const float *scaled,
@@ -84,8 +85,10 @@ static void abs_pow34_v(float *out, const float *in, const int size)
{
#ifndef USE_REALLY_FULL_SEARCH
int i;
- for (i = 0; i < size; i++)
- out[i] = pow(fabsf(in[i]), 0.75);
+ for (i = 0; i < size; i++) {
+ float a = fabsf(in[i]);
+ out[i] = sqrtf(a * sqrtf(a));
+ }
#endif /* USE_REALLY_FULL_SEARCH */
}
@@ -110,7 +113,7 @@ static float quantize_band_cost(struct AACEncContext *s, const float *in,
const int dim = cb < FIRST_PAIR_BT ? 4 : 2;
int resbits = 0;
#ifndef USE_REALLY_FULL_SEARCH
- const float Q34 = pow(Q, 0.75);
+ const float Q34 = sqrtf(Q * sqrtf(Q));
const int range = aac_cb_range[cb];
const int maxval = aac_cb_maxval[cb];
int offs[4];
@@ -225,7 +228,7 @@ static void quantize_and_encode_band(struct AACEncContext *s, PutBitContext *pb,
const int dim = (cb < FIRST_PAIR_BT) ? 4 : 2;
int i, j, k;
#ifndef USE_REALLY_FULL_SEARCH
- const float Q34 = pow(Q, 0.75);
+ const float Q34 = sqrtf(Q * sqrtf(Q));
const int range = aac_cb_range[cb];
const int maxval = aac_cb_maxval[cb];
int offs[4];
--
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