Author: Vincent Diepeveen
Date: 13:07:33 09/27/02
Go up one level in this thread
On September 26, 2002 at 19:39:30, Dann Corbit wrote:
>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,
You really want there:
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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