[Bug 18916] Thief 2 crashes when bringing up in-game menu

[wine-bugs at winehq.org]

http://bugs.winehq.org/show_bug.cgi?id=18916





--- Comment #15 from Henri Verbeet <hverbeet at gmail.com>  2009-06-16 08:44:28 ---
(In reply to comment #14)
> How about this then (I take it WORD is unsigned, otherwise this won't quite
> work):
> 
>     WORD d15 = source[x] & 0xfffe;
>     DWORD d24 = (d15 << 8) + (d15 >> 7);
> 
> ?  Saves multiplies and more importantly divides and is pretty accurate:
> effectively I've rewritten 
> 
>     1/(2^15-1) ~~ 2^-15 + 2^-30
> 
> (the 2^-45 term won't interest us) and so
> 
>     (2^24-1)/(2^15-1) * d15/2  ~~  2^8 d15 + 2^-7 d15 .
> 
> Certainly this works properly for d15 = 0xfffe.  I'm not worried about the
> dangling half bit.  I can do a detailed error analysis if you're not convinced,
> the worst error is just under half a bit -- if we really care, I can try to
> figure out how to get it back, but I'm sure we don't ;-)
> 
That half bit does get rounded up to a whole bit on occasion of course, but I
can live with that. As far as I'm concerned, feel free to submit that as a
patch. You might as well just write "dest[x] = (((source[x] & 0xfffe) << 16) +
((source[x] & 0xff80) << 1)) | (source[x] & 0x1);" though.

> I do this kind of nonsense a lot on the ARM, where divide is to be studiously
> avoided in inner loops!
> 
I don't think it's quite as expensive on modern x86, but it doesn't hurt to
avoid.

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