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New simple and fast bitboard move generator
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Gerd Isenberg



Joined: 08 Mar 2006
Posts: 1785
Location: Hattingen, Germany
PostPost subject: Re: New simple and fast bitboard move generator    Posted: Sun May 06, 2007 11:16 am Reply to topic Reply with quote
In assembly i would try something like this, to use a shared index array with preinitialized registers {0(implicit), 7, 56, 63} to distinguish between different directions if no inner blocking square is found by bitscan. That takes only max two cachelines (if properly 64-byte cacheline-aligned) for the four 2-byte index lookups:

Code:
_rookAttacks PROC
  shl  ecx, 5 ; sq*64

  mov  rax, rdx ; occ
  mov  r8, rdx
  mov  r9, rdx
  mov  r10d, 7
  mov  r11d, 56

  and  rax, QWORD PTR bits[rcx]
  and  r8,  QWORD PTR bits[rcx + 8]
  and  r9,  QWORD PTR bits[rcx + 16]
  and  rdx, QWORD PTR bits[rcx + 24]

  add  ecx, ecx ; *2 assumes short lookop

  bsf  rax, rax
  bsf  r10,  r8
  mov  r8d, 63
  bsr  r11,  r9
  bsr  r8, rdx

  movzx eax,WORD PTR index[rcx + 2*rax] ; *2 assumes short lookop
  or    ax, WORD PTR index[rcx + 2*r10]
  or    ax, WORD PTR index[rcx + 2*r11]
  or    ax, WORD PTR index[rcx + 2*r8]
 
  mov   rax, QWORD PTR rookLookup[8*rax]
  ret   0
_rookAttacks ENDP

But if i try this C-Code, the generated assembly unfortunately looks very ugly.

Code:
u64 rookAttacks(u64 occ, u32 sq) {
    unsigned long ln = 0, le = 7, ls = 56, lw = 63;
    _BitScanForward64(&ln, occ & bits[sq][0]);
    _BitScanForward64(&le, occ & bits[sq][1]);
    _BitScanReverse64(&ls, occ & bits[sq][2]);
    _BitScanReverse64(&lw, occ & bits[sq][3]);
    u32 idx = index[sq][ln] | index[sq][le] | index[sq][ls] | index[sq][lw];
    return rookLookup[idx];
}
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Subject Author Date/Time
New simple and fast bitboard move generator Michael Sherwin Sat May 05, 2007 3:52 pm
      Re: New simple and fast bitboard move generator Gerd Isenberg Sat May 05, 2007 5:43 pm
            Re: New simple and fast bitboard move generator Gerd Isenberg Sun May 06, 2007 8:52 am
                  Re: New simple and fast bitboard move generator Michael Sherwin Sun May 06, 2007 10:31 am
                        Re: New simple and fast bitboard move generator Gerd Isenberg Sun May 06, 2007 11:16 am
                              Re: New simple and fast bitboard move generator Michael Sherwin Sun May 06, 2007 1:21 pm
                                    Re: New simple and fast bitboard move generator Gerd Isenberg Sun May 06, 2007 1:52 pm
                                          Re: New simple and fast bitboard move generator Michael Sherwin Sun May 06, 2007 3:15 pm
                              Re: New simple and fast bitboard move generator Michael Sherwin Sun May 06, 2007 10:29 pm
                                    Re: New simple and fast bitboard move generator Gerd Isenberg Mon May 07, 2007 8:40 am
                                          Re: New simple and fast bitboard move generator Michael Sherwin Mon May 07, 2007 11:06 am
                                          Re: New simple and fast bitboard move generator Gerd Isenberg Mon May 07, 2007 8:08 pm
                                                Re: New simple and fast bitboard move generator Gerd Isenberg Mon May 07, 2007 11:22 pm
                                                      Re: New simple and fast bitboard move generator Michael Sherwin Tue May 08, 2007 3:18 am
                                                            Re: New simple and fast bitboard move generator Gerd Isenberg Tue May 08, 2007 6:11 am
                                                Re: New simple and fast bitboard move generator Michael Sherwin Tue May 08, 2007 9:25 pm
                                                      Re: New simple and fast bitboard move generator Michael Sherwin Tue May 08, 2007 10:55 pm
                                                      Re: New simple and fast bitboard move generator Gerd Isenberg Wed May 09, 2007 3:18 am
                                                            Re: New simple and fast bitboard move generator Tony Wed May 09, 2007 6:10 am
                                                                  Re: New simple and fast bitboard move generator Michael Sherwin Wed May 09, 2007 7:47 am
                                                                        Re: New simple and fast bitboard move generator Tony Wed May 09, 2007 8:24 am
                                                      Re: New simple and fast bitboard move generator Gerd Isenberg Wed May 09, 2007 7:31 pm
                                                            Re: New simple and fast bitboard move generator Michael Sherwin Wed May 09, 2007 11:30 pm
            Re: New simple and fast bitboard move generator Tony Mon May 07, 2007 6:46 am
                  Re: New simple and fast bitboard move generator Gerd Isenberg Mon May 07, 2007 8:51 am
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