Author: Dann Corbit
Date: 16:39:30 09/26/02
Go up one level in this thread
On September 26, 2002 at 15:05:39, Dieter Buerssner wrote:
>On September 25, 2002 at 16:51:17, Dann Corbit wrote:
>
>>Here is what my compiler spit out (I could probably choose better flags too):
>
>When I look at the generated code, it seems, you couldn't choose better flags.
>To me, it looks essentially identical to the hand written assembly. The few
>differences (slightly other order of things, add eax, 1 instead of inc eax) I
>cannot judge. With my assembler knowledge mainly from 386 days and before, I
>would even trust the compiler more here, than myself writing this in assembler
>(I would come up with practically identical code as well). I could imagine, that
>the compiler knows something about pairing of the instructions, which I don't.
>He could also know better, about which labels should be aligned (perhaps
>dependent on specific processor switches). He can know easily, how many bytes
>each instruction needs. Perhaps using add eax, 1 makes a better alignment in the
>end, than the shorter inc eax.
>
>Gcc also produced practically the same code.
An aside:
This is faster for me:
static int inbits[256] = {
0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8,
};
int Count(const BITBOARD B)
{
return inbits[(unsigned char) B] +
inbits[(unsigned char) (B >> 8)] +
inbits[(unsigned char) (B >> 16)] +
inbits[(unsigned char) (B >> 24)] +
inbits[(unsigned char) (B >> 32)] +
inbits[(unsigned char) (B >> 40)] +
inbits[(unsigned char) (B >> 48)] +
inbits[(unsigned char) (B >> 56)];
}
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