On Thu, 8 Aug 2002, Tim Phipps wrote:
[SNIP]
> I can't help feeling that 257 is the wrong number for all this stuff and
> 256 is the correct number. It might be better to just leave most of
> these things as unsigned shorts or pass XColor's around and convert to
> byte size pieces as late as possible.
>
> /257 will take ages on any processor, /256 will take one cycle on most.
257 is the correct scale factor for conversion between 8- and
16-bit colors: 257==0x101, so that e.g. 0xFF becomes 0xFFFF if multiplied
by 0x101, not 0x100. Most of XFree86 code uses 0x101 as conversion factor
(see xc/{lib/X11/LRGB.c,programs/xcmsdb/xcmsdb.c}. Of course, when
scaling from 16 down to 8 bits 256 will work almost as good as 257, but
unification-wise 257 is better.
_________________________________________
Dmitry Yu. Bolkhovityanov
The Budker Institute of Nuclear Physics
Novosibirsk, Russia
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