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Subject: Re: Will the Itanium have a BSF or BSR instruction?

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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