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avcodec/ppc/h264dsp: Fix edge cases for bi-weight on ppc

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S16 saturating sum must be computed dot-product-first. The Altivec code
added the offset to the first product before adding the second product,
so an intermediate saturation could corrupt the result even when the
true sum fits.

Swap the two vec_adds to form the dot product first. This fixes
bi-weight checkasm test for PPC.

Signed-off-by: Zuxy Meng <zuxy.meng@gmail.com>
This commit is contained in:
Zuxy Meng
2026-09-04 21:18:41 -07:00
parent c80bfd962f
commit 3f77ce4dee
2 changed files with 4 additions and 4 deletions
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4
libavcodec/ppc/h264dsp.c
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@@ -749,16 +749,16 @@ void biweight_h264_W_altivec(uint8_t *dst, uint8_t *src, ptrdiff_t stride, int h
v0 = vec_mladd(v0, vweightd, zero_s16v);
v2 = vec_mladd(v2, vweights, zero_s16v);
v0 = vec_adds(v0, voffset);
v0 = vec_adds(v0, v2);
v0 = vec_adds(v0, voffset);
v0 = vec_sra(v0, vlog2_denom);
}
if (w == 16 || !dst_aligned) {
v1 = vec_mladd(v1, vweightd, zero_s16v);
v3 = vec_mladd(v3, vweights, zero_s16v);
v1 = vec_adds(v1, voffset);
v1 = vec_adds(v1, v3);
v1 = vec_adds(v1, voffset);
v1 = vec_sra(v1, vlog2_denom);
}
vdst = vec_packsu(v0, v1);

4
tests/checkasm/h264dsp.c
View File

@@ -544,8 +544,8 @@ static void check_weight(void)
}
}
// only arch that can pass test
#define H264_CHECK_BIWEIGHT ARCH_X86
// only archs that can pass test
#define H264_CHECK_BIWEIGHT (ARCH_X86 || ARCH_PPC)
#if H264_CHECK_BIWEIGHT
static void check_biweight(void)