Commit db56526f14794c48f18c1c90c1bc2a51bdedcacf
2021-06-10T13:07:27
audiocvt: Replace divisions Division is expensive and the compiler can not replace it themselves. Though we now we will be ok in terms of floating point edge behaviour.
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diff --git a/src/audio/SDL_audiocvt.c b/src/audio/SDL_audiocvt.c
index 603e7db..efeb538 100644
--- a/src/audio/SDL_audiocvt.c
+++ b/src/audio/SDL_audiocvt.c
@@ -104,6 +104,7 @@ SDL_Convert51ToStereo(SDL_AudioCVT * cvt, SDL_AudioFormat format)
float *dst = (float *) cvt->buf;
const float *src = dst;
int i;
+ const float two_fifths = 1.0f / 2.5f;
LOG_DEBUG_CONVERT("5.1", "stereo");
SDL_assert(format == AUDIO_F32SYS);
@@ -111,8 +112,8 @@ SDL_Convert51ToStereo(SDL_AudioCVT * cvt, SDL_AudioFormat format)
/* SDL's 5.1 layout: FL+FR+FC+LFE+BL+BR */
for (i = cvt->len_cvt / (sizeof (float) * 6); i; --i, src += 6, dst += 2) {
const float front_center_distributed = src[2] * 0.5f;
- dst[0] = (src[0] + front_center_distributed + src[4]) / 2.5f; /* left */
- dst[1] = (src[1] + front_center_distributed + src[5]) / 2.5f; /* right */
+ dst[0] = (src[0] + front_center_distributed + src[4]) * two_fifths; /* left */
+ dst[1] = (src[1] + front_center_distributed + src[5]) * two_fifths; /* right */
}
cvt->len_cvt /= 3;
@@ -152,6 +153,7 @@ SDL_Convert71To51(SDL_AudioCVT * cvt, SDL_AudioFormat format)
float *dst = (float *) cvt->buf;
const float *src = dst;
int i;
+ const float two_thirds = 1.0f / 1.5f;
LOG_DEBUG_CONVERT("7.1", "5.1");
SDL_assert(format == AUDIO_F32SYS);
@@ -159,12 +161,12 @@ SDL_Convert71To51(SDL_AudioCVT * cvt, SDL_AudioFormat format)
for (i = cvt->len_cvt / (sizeof (float) * 8); i; --i, src += 8, dst += 6) {
const float surround_left_distributed = src[6] * 0.5f;
const float surround_right_distributed = src[7] * 0.5f;
- dst[0] = (src[0] + surround_left_distributed) / 1.5f; /* FL */
- dst[1] = (src[1] + surround_right_distributed) / 1.5f; /* FR */
- dst[2] = src[2] / 1.5f; /* CC */
- dst[3] = src[3] / 1.5f; /* LFE */
- dst[4] = (src[4] + surround_left_distributed) / 1.5f; /* BL */
- dst[5] = (src[5] + surround_right_distributed) / 1.5f; /* BR */
+ dst[0] = (src[0] + surround_left_distributed) * two_thirds; /* FL */
+ dst[1] = (src[1] + surround_right_distributed) * two_thirds; /* FR */
+ dst[2] = src[2] * two_thirds; /* CC */
+ dst[3] = src[3] * two_thirds; /* LFE */
+ dst[4] = (src[4] + surround_left_distributed) * two_thirds; /* BL */
+ dst[5] = (src[5] + surround_right_distributed) * two_thirds; /* BR */
}
cvt->len_cvt /= 8;
@@ -182,6 +184,7 @@ SDL_Convert51ToQuad(SDL_AudioCVT * cvt, SDL_AudioFormat format)
float *dst = (float *) cvt->buf;
const float *src = dst;
int i;
+ const float two_thirds = 1.0f / 1.5f;
LOG_DEBUG_CONVERT("5.1", "quad");
SDL_assert(format == AUDIO_F32SYS);
@@ -190,10 +193,10 @@ SDL_Convert51ToQuad(SDL_AudioCVT * cvt, SDL_AudioFormat format)
/* SDL's 5.1 layout: FL+FR+FC+LFE+BL+BR */
for (i = cvt->len_cvt / (sizeof (float) * 6); i; --i, src += 6, dst += 4) {
const float front_center_distributed = src[2] * 0.5f;
- dst[0] = (src[0] + front_center_distributed) / 1.5f; /* FL */
- dst[1] = (src[1] + front_center_distributed) / 1.5f; /* FR */
- dst[2] = src[4] / 1.5f; /* BL */
- dst[3] = src[5] / 1.5f; /* BR */
+ dst[0] = (src[0] + front_center_distributed) * two_thirds; /* FL */
+ dst[1] = (src[1] + front_center_distributed) * two_thirds; /* FR */
+ dst[2] = src[4] * two_thirds; /* BL */
+ dst[3] = src[5] * two_thirds; /* BR */
}
cvt->len_cvt /= 6;