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audio: Added SSE3 implementation of SDL_ConvertStereoToMono().

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icculus committed Jan 23, 2017
1 parent a7f86f2 commit 64056e81cd419eb9848ba6e9e859fb8d5f6875bd
Showing with 58 additions and 1 deletion.
  1. +58 −1 src/audio/SDL_audiocvt.c
@@ -29,6 +29,50 @@
#include "SDL_assert.h"
#include "../SDL_dataqueue.h"

/* !!! FIXME: wire this up to the configure script, etc. */
#include "SDL_cpuinfo.h"
#define HAVE_SSE3_INTRINSICS 0

#if HAVE_SSE3_INTRINSICS
#include <pmmintrin.h>
#endif

#if HAVE_SSE3_INTRINSICS
/* Effectively mix right and left channels into a single channel */
static void SDLCALL
SDL_ConvertStereoToMono_SSE3(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
float *dst = (float *) cvt->buf;
const float *src = dst;
int i = cvt->len_cvt / 8;

LOG_DEBUG_CONVERT("stereo", "mono (using SSE3)");
SDL_assert(format == AUDIO_F32SYS);

/* We can only do this if dst is aligned to 16 bytes; since src is the
same pointer and it moves by 2, it can't be forcibly aligned. */
if ((((size_t) dst) & 15) == 0) {
/* Aligned! Do SSE blocks as long as we have 16 bytes available. */
const __m128 divby2 = _mm_set1_ps(0.5f);
while (i >= 4) { /* 4 * float32 */
_mm_store_ps(dst, _mm_mul_ps(_mm_hadd_ps(_mm_load_ps(src), _mm_load_ps(src+4)), divby2));
i -= 4; src += 8; dst += 4;
}
}

/* Finish off any leftovers with scalar operations. */
while (i) {
*dst = (src[0] + src[1]) * 0.5f;
dst++; i--; src += 2;
}

cvt->len_cvt /= 2;
if (cvt->filters[++cvt->filter_index]) {
cvt->filters[cvt->filter_index] (cvt, format);
}
}
#endif

/* Effectively mix right and left channels into a single channel */
static void SDLCALL
SDL_ConvertStereoToMono(SDL_AudioCVT * cvt, SDL_AudioFormat format)
@@ -579,7 +623,20 @@ SDL_BuildAudioCVT(SDL_AudioCVT * cvt,
*/
while (((src_channels % 2) == 0) &&
((src_channels / 2) >= dst_channels)) {
cvt->filters[cvt->filter_index++] = SDL_ConvertStereoToMono;
SDL_AudioFilter filter = NULL;

#if HAVE_SSE3_INTRINSICS
if (SDL_HasSSE3()) {
filter = SDL_ConvertStereoToMono_SSE3;
}
#endif

if (!filter) {
filter = SDL_ConvertStereoToMono;
}

cvt->filters[cvt->filter_index++] = filter;

src_channels /= 2;
cvt->len_ratio /= 2;
}

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