Author: J. Wesley Cleveland
Date: 11:12:25 08/17/00
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On August 16, 2000 at 13:11:04, Eugene Nalimov wrote: >On August 15, 2000 at 23:27:46, Larry Griffiths wrote: > >>I looked through some literature for the Intel Itanium processor and did not see >>any Bit Scan Forward or Bit Scan reverse instructions. Does anyone know for >>sure if the Itanium has these instructions or something like them. >>My bitboard move generation would really suck without BSF or BSR. >> >>Larry. > >No. There are no such instructions. You have to use ifs, shifts, and lookup >table. Here is the example -- FirstOne()/LastOne() that I wrote for IA-64 >version of Crafty (it is not in the official build yet): > I think you can do a lot better using the multimedia instructions (this is just from reading the docs). int FirstOne(BITBOARD arg1) { __asm { ld r1, arg1 ld r2, 0fefefefefefefefeh ; probably is address of constant ld r3, 0101010101010101h padd1.uuu r4=r1,r2 ; each byte in r4 has fe if byte in arg1 was 0, else ff padd r4=r4,r3 ; now each non-zero byte in arg1 is zero czx1.l r2=r4 ; r2 has byte with first bit set or 8 if all 0 shl r2=r2,3 shr.u r1=r1,r2 ;first bit is now in low byte (or 0 if none set) and r1, 0ffh ld r0, btab[r1] ;not sure how to do this add r0=r0,r2
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