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Two small in-register-lookups
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Gerd Isenberg



Joined: 08 Mar 2006
Posts: 1785
Location: Hattingen, Germany
PostPost subject: Re: Two small in-register-lookups    Posted: Tue Apr 24, 2007 10:58 am Reply to topic Reply with quote
jwes wrote:
Gerd Isenberg wrote:
Color of square - assumes 32-bit shift by mod 32.
Is that portable for 32-bit ints?
(otherwise sq&31 or sq&15 is necessary)

Code:
unsigned int colorOfSquare (unsigned int sq) {
   return  (0xAA55AA55 >> sq) & 1;
}


or
Code:
unsigned int colorOfSquare (unsigned int sq) {
   return  ((sq>>3)^ sq) & 1;
}


Yes, I am aware of that. It has one dependent instruction more and with my mapping (a1 == 0, -> dark square), I even need one additional xor 1 or not Wink

Thus loading the immediate constant to eax, plus shift, mask looks not that bad, despite variable shift needs cl.

Code:
; ecx == sq
mov eax, AA55AA55H
shr eax, cl
and eax, 1
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Display posts from previous:   
Subject Author Date/Time
Two small in-register-lookups Gerd Isenberg Mon Apr 23, 2007 10:28 pm
      Re: Two small in-register-lookups J. Wesley Cleveland Tue Apr 24, 2007 9:08 am
            Re: Two small in-register-lookups H.G.Muller Tue Apr 24, 2007 9:51 am
                  Re: Two small in-register-lookups Gerd Isenberg Tue Apr 24, 2007 11:00 am
            Re: Two small in-register-lookups Gerd Isenberg Tue Apr 24, 2007 10:58 am
                  Re: Two small in-register-lookups H.G.Muller Tue Apr 24, 2007 12:37 pm
                        Re: Two small in-register-lookups Gerd Isenberg Tue Apr 24, 2007 6:36 pm
                              Re: Two small in-register-lookups Gerd Isenberg Tue Apr 24, 2007 8:11 pm
                                    Re: Two small in-register-lookups H.G.Muller Tue Apr 24, 2007 9:48 pm
                                          Re: Two small in-register-lookups Gerd Isenberg Tue Apr 24, 2007 9:57 pm
                                                Re: Two small in-register-lookups Tord Romstad Wed Apr 25, 2007 7:40 am
                                                      Re: Two small in-register-lookups H.G.Muller Wed Apr 25, 2007 9:49 am
                                                            Re: Two small in-register-lookups Tord Romstad Wed Apr 25, 2007 10:53 am
                                                                  Re: Two small in-register-lookups H.G.Muller Wed Apr 25, 2007 12:01 pm
                                                      Re: Two small in-register-lookups Gerd Isenberg Fri Apr 27, 2007 7:41 pm
                        Re: Two small in-register-lookups Gerd Isenberg Fri Apr 27, 2007 7:44 pm
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