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lavc/exrdsp: unroll predictor

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With explicit unrolling, we can skip half of the sign bit flips, and
the compiler is then better able to optimise the scalar loop:

predictor_c: 31376.0 (before)
predictor_c: 23703.0 (after)
This commit is contained in:
Rémi Denis-Courmont 2023-11-11 17:08:45 +02:00
parent c536e92207
commit ce467421dc
1 changed files with 13 additions and 3 deletions
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16
libavcodec/exrdsp.c
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@ -40,10 +40,20 @@ static void reorder_pixels_scalar(uint8_t *dst, const uint8_t *src, ptrdiff_t si
static void predictor_scalar(uint8_t *src, ptrdiff_t size)
{
ptrdiff_t i;
/* Unrolled: `src[i + 1] += src[i] - 128;` */
if ((size & 1) == 0) {
src[1] += src[0] ^ 0x80;
src++;
size--;
}
for (i = 1; i < size; i++)
src[i] += src[i-1] - 128;
for (ptrdiff_t i = 1; i < size; i += 2) {
uint8_t a = src[i] + src[i - 1];
src[i] = a;
src[i + 1] += a;
src[i] ^= 0x80;
}
}
av_cold void ff_exrdsp_init(ExrDSPContext *c)