Uh, I don’t know how I may introduce this one. I don’t know if I should call it a horrific failure or just hilarious. This is what comes out of VS2008 for a signed short division:
symSend = mergedNGram % numCases;
mergedNGram /= numCases;
The produced code:
00024 0f bf 86 2c 04
[...]
You never stop learning, I just explored how I can force a compiler into producing the sbb op on x86. It’s quite difficult actually, most of them produce for example cmp + seta + neg for the term -(a > b). In fact the only deterministic behaviour is with a very special ternery term (a [...]
Havn’t found this anywhere, so I had to do it myself. The title says it all, so here it is without drama:
// mm7 = 0×8000 0×8000 0×8000 0×8000
// mm3 = 0×7FFF 0xFFFF 0×7FFF 0xFFFF
// mm5 = 0×7FFF 0×7FFF 0xFFFF 0xFFFF
movq mm6, mm7
pand mm7, mm5 /* b ? 0 | 0×8000 */
pand mm6, mm3 /* a ? 0 | 0×8000 */
pxor mm5, [...]
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