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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.
This commit is contained in:
Joel Linn 2021-06-10 13:07:27 +02:00 committed by Ryan C. Gordon
parent e1c3a25034
commit db56526f14
1 changed files with 15 additions and 12 deletions
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27
src/audio/SDL_audiocvt.c
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@ -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;