[Mesa-dev] [PATCH 2/2] mesa: fix unpack_ARGB1555_REV()

[Michel Dänzer]

On Don, 2011-12-01 at 07:28 -0700, Brian Paul wrote: 
> On 12/01/2011 02:42 AM, Michel Dänzer wrote:
> > On Mit, 2011-11-30 at 20:36 -0700, Brian Paul wrote:
> >
> >> diff --git a/src/mesa/main/format_unpack.c b/src/mesa/main/format_unpack.c
> >> index 4b4ee6b..fc0db34 100644
> >> --- a/src/mesa/main/format_unpack.c
> >> +++ b/src/mesa/main/format_unpack.c
> >> @@ -275,10 +275,11 @@ unpack_ARGB1555_REV(const void *src, GLfloat dst[][4], GLuint n)
> >>      const GLushort *s = ((const GLushort *) src);
> >>      GLuint i;
> >>      for (i = 0; i<  n; i++) {
> >> -      dst[i][RCOMP] = UBYTE_TO_FLOAT( ((s[i]>>   7)&  0xf8) | ((s[i]>>  12)&  0x7) );
> >> -      dst[i][GCOMP] = UBYTE_TO_FLOAT( ((s[i]>>   2)&  0xf8) | ((s[i]>>   7)&  0x7) );
> >> -      dst[i][BCOMP] = UBYTE_TO_FLOAT( ((s[i]<<   3)&  0xf8) | ((s[i]>>   2)&  0x7) );
> >> -      dst[i][ACOMP] = UBYTE_TO_FLOAT( ((s[i]>>  15)&  0x01) * 255 );
> >> +      GLushort tmp = (s[i]<<  8) | (s[i]>>  8); /* byteswap */
> >
> > A BSWAP16() macro might be nice for this, but I wouldn't let that hold
> > up this fix.
> >
> >> +      dst[i][RCOMP] = UBYTE_TO_FLOAT( ((tmp>>   7)&  0xf8) | ((tmp>>  12)&  0x7) );
> >> +      dst[i][GCOMP] = UBYTE_TO_FLOAT( ((tmp>>   2)&  0xf8) | ((tmp>>   7)&  0x7) );
> >> +      dst[i][BCOMP] = UBYTE_TO_FLOAT( ((tmp<<   3)&  0xf8) | ((tmp>>   2)&  0x7) );
> >
> > Don't these lines need to be changed to be the same as in
> > unpack_ARGB1555()?
> 
> It should be equivalent (lookup table vs. arithmetic).  It would nice 
> if someone could write a little benchmark to see which is really faster.

I still don't understand why these lines should be different between
unpack_ARGB1555_REV() and unpack_ARGB1555(), as the only difference
between the two formats is the swapped bytes, right? If both variants
are equivalent, I don't particularly care which one is considered
better, but I think the other one should be adapted to match.


-- 
Earthling Michel Dänzer           |                   http://www.amd.com
Libre software enthusiast         |          Debian, X and DRI developer