Author: Gerd Isenberg
Date: 07:07:55 07/11/03
Go up one level in this thread
On July 11, 2003 at 08:41:46, Uri Blass wrote:
>On July 11, 2003 at 08:04:48, Gerd Isenberg wrote:
>
>>On July 10, 2003 at 23:04:04, Uri Blass wrote:
>>
>>>I have in movei cases when I have 2 lines like the following when s can be only
>>>0 or 1 and 128 can be every power of 2 that is less than 2^16
>>>
>>>directsee[target]|=(128<<(s<<4));
>>>directsee[target]&=~(128<<((1^s)<<4));
>>>
>>>My question is if there is a way to optimize it.
>>>
>>>There are also case when I know s and may have something like the following:
>>>
>>>directsee[target]|=64;
>>>directsee[target]&=~(64<<16);
>>>
>>>I do not know if there is a way to do it faster(I expect a smart compiler to
>>>optimize it by itself).
>>>
>>>Uri
>>
>>Hi Uri,
>>
>>directsee[target] |=(128<<(s<<4));
>>
>>assuming directsee is 32 bit array:
>>
>>s ==> {0,1}
>>s << 4 ==> {0,16}
>>0x00000080 << (s << 4) ==> {0x00000080, 0x00800000}
>>
>>what about a union of directsee with one 32 bit int and two short 16-bit ints
>>and to write:
>>
>>directsee[target].short16[s] |= 128;
>>
>>Cheers,
>>Gerd
>
>I will try it
>
>I understand that
>directsee[target]&=~(128<<((1^s)<<4)) should be translated to
>directsee[target].short16[1^s]&=~128;
>
>The question is if the following is the fastest or I can do it in a faster way:
>
>directsee[target].short16[s] |= 128;
>directsee[target].short16[1^s]&=~128;
>
>
>Uri
I guess that is quite optimal, one c-statement should be translated to one (or
two) asm-statements, like this:
; target = edi; s = ebx
or word ptr [_directsee + 4*edi + 2*ebx], 0x0080
xor ebx, 1
and word ptr [_directsee + 4*edi + 2*ebx], 0xff7f
Gerd
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