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Correct rounding in divide-by-255 code. Obtained from xserver.

This commit is contained in:
Eric Anholt 2006-01-04 00:05:16 +00:00
parent b9c0ae867e
commit b6b88d2f62
2 changed files with 9 additions and 4 deletions
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5
ChangeLog
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@ -1,3 +1,8 @@
2006-01-03 Eric Anholt <anholt@FreeBSD.org>
* render/picture.c: (premultiply):
Correct rounding in divide-by-255 code. Obtained from xserver.
2006-01-03 Eric Anholt <anholt@FreeBSD.org>
* hw/xgl/xglpict.c: (xglPictureInit):

8
render/picture.c
View File

@ -863,12 +863,12 @@ static CARD32 xRenderColorToCard32(xRenderColor c)
static unsigned int premultiply(unsigned int x)
{
unsigned int a = x >> 24;
unsigned int t = (x & 0xff00ff) * a;
t = (t + ((t >> 8) & 0xff00ff) + 0x800080) >> 8;
unsigned int t = (x & 0xff00ff) * a + 0x800080;
t = (t + ((t >> 8) & 0xff00ff)) >> 8;
t &= 0xff00ff;
x = ((x >> 8) & 0xff) * a;
x = (x + ((x >> 8) & 0xff) + 0x80);
x = ((x >> 8) & 0xff) * a + 0x80;
x = (x + ((x >> 8) & 0xff));
x &= 0xff00;
x |= t | (a << 24);
return x;