Author: Ricardo Gibert
Date: 18:15:17 01/22/02
Go up one level in this thread
On January 21, 2002 at 16:16:10, Rafael Andrist wrote:
>Well, I just rewrote the following function in assembler to get better speed (no
>conditional jumps, less memory access) but the speedup was only minimal. A
>possible problem of the asm code is, that the instructions doesn't pair well,
>but it should be still considerably faster. Has anyone an idea what the problem
>with the code below is? Should I perhaps throw this function out and use a
>look-up-table?
>
>INLINE int Diag045Rot(const int iSqNr)
>{
>#if defined (Use_Asm)
>// 0 <= iSqNr <= 63
>__asm
>{
> mov eax, iFeldNr;
> mov ah, al;
> and al, 007h; //x (iFeldNr%8) --> al
> shr ah, 3; //y (iFeldNr/8) --> ah
> sub al, ah; //x-y --> al
> mov ah, al; // --> ah
> and ah, 080h; //ah &= 0x80 (isolate sign bit)
> add ah, 080h; //ah += 0x80 (setting the carry bit)
> adc ah, 0; //ah += carry bit
> shl ah, 3; //ah <<= 3;
> add al, ah; //al += 8*(x-y < 0)
> xor ah, ah;
>}
>#else
> int x, y;
> x = iSqNr%8;
> y = iSqNr/8;
> return x-y + 8*(x-y < 0);
Isn't this is the same as "return abs(x-y);"? If so, maybe the compiler will do
a better job of optimizing with it.
Also, if you are using msvc6, it might help the compiler to insert an
"__assume((0 <= iSqNr) && (iSqNr <= 63));". I don't use msvc6 myself, so I can't
tell you if this really helps here.
>#endif
>}
>
>
>Thanks in Advance
>Rafael B. Andrist
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