Author: Anthony Cozzie
Date: 08:08:32 01/06/04
Go up one level in this thread
>>It isn't. Bitboards are slower than attack tables on 32 bit hardware. For
>>example, a 64 bit shift on 32 bit hardware is something like 10 instructions and
>>includes a conditional branch.
>
>On x86-32 64-bit shift are two instructions only, 7 bytes opcode:
>
>shld edx,ecx,9
>shl ecx,9
>
>shrd ecx,edx,7
>shr edx,7
This is how VC7 codes up a 64 bit shift:
_allshr PROC NEAR
;
; Handle shifts of 64 bits or more (if shifting 64 bits or more, the result
; depends only on the high order bit of edx).
;
cmp cl,64
jae short RETSIGN
;
; Handle shifts of between 0 and 31 bits
;
cmp cl, 32
jae short MORE32
shrd eax,edx,cl
sar edx,cl
ret
;
; Handle shifts of between 32 and 63 bits
;
MORE32:
mov eax,edx
sar edx,31
and cl,31
sar eax,cl
ret
;
; Return double precision 0 or -1, depending on the sign of edx
;
RETSIGN:
sar edx,31
mov eax,edx
ret
anthony
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.