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Make pix_add_mul() in pixman-mmx.c produce exact results.

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Previously this routine would compute (x * a + y * b) / 255. Now it
computes (x * a) / 255 + (y * b) / 255, so that the results are
bitwise equivalent to the non-mmx versions.
This commit is contained in:
Søren Sandmann Pedersen 2009-08-06 22:42:25 -04:00
parent f7463ffafb
commit a075a870fd
1 changed files with 6 additions and 13 deletions
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19
pixman/pixman-mmx.c
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@ -400,25 +400,18 @@ pack_565 (__m64 pixel, __m64 target, int pos)
static force_inline __m64
pix_add_mul (__m64 x, __m64 a, __m64 y, __m64 b)
{
x = _mm_mullo_pi16 (x, a);
y = _mm_mullo_pi16 (y, b);
x = _mm_adds_pu16 (x, MC (4x0080));
x = _mm_adds_pu16 (x, y);
x = _mm_adds_pu16 (x, _mm_srli_pi16 (x, 8));
x = _mm_srli_pi16 (x, 8);
x = pix_multiply (x, a);
y = pix_multiply (y, b);
return x;
return pix_add (x, y);
}
#else
#define pix_add_mul(x, a, y, b) \
( x = _mm_mullo_pi16 (x, a), \
y = _mm_mullo_pi16 (y, b), \
x = _mm_adds_pu16 (x, MC (4x0080)), \
x = _mm_adds_pu16 (x, y), \
x = _mm_adds_pu16 (x, _mm_srli_pi16 (x, 8)), \
_mm_srli_pi16 (x, 8) )
( x = pix_multiply (x, a), \
y = pix_multiply (y, a), \
pix_add (x, y) )
#endif