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use xorps instead of mulps to toggle the sign of a float, as suggested by Software Optimization Guide for AMD64 Processors. 

Patch by Zuxy Meng < zuxy POIS meng AH  gmail POIS com > OKed by Michael
Original thread:
Date: Mar 5, 2006 8:15 PM
Subject: [Ffmpeg-devel] [PATCH] Little optimization to fft_sse.c

Originally committed as revision 5112 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Zuxy Meng 2006-03-05 20:25:18 +00:00 committed by Guillaume Poirier
parent d84f7c61ee
commit 2ffb22d2ad
1 changed files with 10 additions and 10 deletions
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20
libavcodec/i386/fft_sse.c
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@ -23,14 +23,14 @@
#include <xmmintrin.h>
static const float p1p1p1m1[4] __attribute__((aligned(16))) =
{ 1.0, 1.0, 1.0, -1.0 };
static const int p1p1p1m1[4] __attribute__((aligned(16))) =
{ 0, 0, 0, 1 << 31 };
static const float p1p1m1p1[4] __attribute__((aligned(16))) =
{ 1.0, 1.0, -1.0, 1.0 };
static const int p1p1m1p1[4] __attribute__((aligned(16))) =
{ 0, 0, 1 << 31, 0 };
static const float p1p1m1m1[4] __attribute__((aligned(16))) =
{ 1.0, 1.0, -1.0, -1.0 };
static const int p1p1m1m1[4] __attribute__((aligned(16))) =
{ 0, 0, 1 << 31, 1 << 31 };
#if 0
static void print_v4sf(const char *str, __m128 a)
@ -58,7 +58,6 @@ void ff_fft_calc_sse(FFTContext *s, FFTComplex *z)
r = (__m128 *)&z[0];
c1 = *(__m128 *)p1p1m1m1;
c2 = *(__m128 *)p1p1p1m1;
if (s->inverse)
c2 = *(__m128 *)p1p1m1p1;
else
@ -68,19 +67,20 @@ void ff_fft_calc_sse(FFTContext *s, FFTComplex *z)
do {
a = r[0];
b = _mm_shuffle_ps(a, a, _MM_SHUFFLE(1, 0, 3, 2));
a = _mm_mul_ps(a, c1);
a = _mm_xor_ps(a, c1);
/* do the pass 0 butterfly */
a = _mm_add_ps(a, b);
a1 = r[1];
b = _mm_shuffle_ps(a1, a1, _MM_SHUFFLE(1, 0, 3, 2));
a1 = _mm_mul_ps(a1, c1);
a1 = _mm_xor_ps(a1, c1);
/* do the pass 0 butterfly */
b = _mm_add_ps(a1, b);
/* multiply third by -i */
/* by toggling the sign bit */
b = _mm_shuffle_ps(b, b, _MM_SHUFFLE(2, 3, 1, 0));
b = _mm_mul_ps(b, c2);
b = _mm_xor_ps(b, c2);
/* do the pass 1 butterfly */
r[0] = _mm_add_ps(a, b);