Optimization chance for following Bit-Operations?

Question

Do you think there is room for optimizations in the function haswon (see below)?

I recognized that changing the argument type from __int64 to unsigned __int64 made the function faster, thus i thougt maybe there is still a chance for optimization.

In more detail: I am writing a connect four game. Recently i used the Profiler Very Sleepy and recognized that the function haswon uses much of the cpu-time. The function uses a bitboard-representation of the connect-four-board for one player. The function itself i found in the sources of the fourstones benchmark. The bitboard representation is following:

.  .  .  .  .  .  .  TOP
5 12 19 26 33 40 47
4 11 18 25 32 39 46
3 10 17 24 31 38 45
2  9 16 23 30 37 44
1  8 15 22 29 36 43
0  7 14 21 28 35 42  BOTTOM

The function:

// return whether newboard includes a win
bool haswon(unsigned __int64 newboard)
{
    unsigned __int64 y = newboard & (newboard >> 6);
    if (y & (y >> 2 * 6)) // check \ diagonal
        return true;
    y = newboard & (newboard >> 7);
    if (y & (y >> 2 * 7)) // check horizontal -
        return true;
    y = newboard & (newboard >> 8);
    if (y & (y >> 2 * 8)) // check / diagonal
        return true;
    y = newboard & (newboard >> 1);
    if (y & (y >> 2))     // check vertical |
        return true;
    return false;
}

Thanks!

Edit: CPU is x86, 32 Bit Architecture, i'm using the Compiler from the Visual Studio 2008 Express Edition. Optimization Flags are /O2 /Oi /GL.

I tried the function haswon2 which Ben Jackson suggested. The assemblies from the Microsoft Compiler, with the default optimization flags for release versions (/O2 /Oi /GL), showing nearly no runtime differences. It looks like that the VC-Compiler in comparison to gcc can not take advantage that it must not evaluate each condition in strict order.

Results: haswon original:

haswon2 from Ben Jackson:

Edit2: Assembly of haswon:

00401A10  mov         eax,dword ptr [esp+4] 
00401A14  mov         ecx,dword ptr [esp+8] 
00401A18  push        ebx  
00401A19  push        esi  
00401A1A  push        edi  
00401A1B  mov         edx,eax 
00401A1D  mov         edi,ecx 
00401A1F  shrd        edx,edi,6 
00401A23  mov         esi,edx 
00401A25  shr         edi,6 
00401A28  and         esi,eax 
00401A2A  and         edi,ecx 
00401A2C  mov         edx,esi 
00401A2E  mov         ebx,edi 
00401A30  shrd        edx,ebx,0Ch 
00401A34  shr         ebx,0Ch 
00401A37  and         edx,esi 
00401A39  and         ebx,edi 
00401A3B  or          edx,ebx 
00401A3D  je          `anonymous namespace'::haswon+35h (401A45h) 
00401A3F  mov         al,1 
00401A41  pop         edi  
00401A42  pop         esi  
00401A43  pop         ebx  
00401A44  ret              
00401A45  mov         edx,eax 
00401A47  mov         edi,ecx 
00401A49  shrd        edx,edi,7 
00401A4D  mov         esi,edx 
00401A4F  shr         edi,7 
00401A52  and         esi,eax 
00401A54  and         edi,ecx 
00401A56  mov         edx,esi 
00401A58  mov         ebx,edi 
00401A5A  shrd        edx,ebx,0Eh 
00401A5E  shr         ebx,0Eh 
00401A61  and         edx,esi 
00401A63  and         ebx,edi 
00401A65  or          edx,ebx 
00401A67  jne         `anonymous namespace'::haswon+2Fh (401A3Fh) 
00401A69  mov         edx,eax 
00401A6B  mov         edi,ecx 
00401A6D  shrd        edx,edi,8 
00401A71  mov         esi,edx 
00401A73  shr         edi,8 
00401A76  and         esi,eax 
00401A78  and         edi,ecx 
00401A7A  mov         edx,esi 
00401A7C  mov         ebx,edi 
00401A7E  shrd        edx,ebx,10h 
00401A82  shr         ebx,10h 
00401A85  and         edx,esi 
00401A87  and         ebx,edi 
00401A89  or          edx,ebx 
00401A8B  jne         `anonymous namespace'::haswon+2Fh (401A3Fh) 
00401A8D  mov         edx,eax 
00401A8F  mov         esi,ecx 
00401A91  shrd        edx,esi,1 
00401A95  shr         esi,1 
00401A97  and         esi,ecx 
00401A99  and         edx,eax 
00401A9B  mov         eax,edx 
00401A9D  mov         ecx,esi 
00401A9F  shrd        eax,ecx,2 
00401AA3  shr         ecx,2 
00401AA6  and         eax,edx 
00401AA8  and         ecx,esi 
00401AAA  or          eax,ecx 
00401AAC  jne         `anonymous namespace'::haswon+2Fh (401A3Fh) 
00401AAE  pop         edi  
00401AAF  pop         esi  
00401AB0  xor         al,al 
00401AB2  pop         ebx  
00401AB3  ret    

Answer 1

The idea behind this version is to avoid the strict testing order (the intermediate returns force the compiler to evaluate the conditions one at a time, in order) as well as the branching associated with multiple if statements:

// return whether newboard includes a win
bool haswon2(uint64_t newboard)
{
    uint64_t y = newboard & (newboard >> 6);
    uint64_t z = newboard & (newboard >> 7);
    uint64_t w = newboard & (newboard >> 8);
    uint64_t x = newboard & (newboard >> 1);
    return (y & (y >> 2 * 6)) | // check \ diagonal
           (z & (z >> 2 * 7)) | // check horizontal -
           (w & (w >> 2 * 8)) | // check / diagonal
           (x & (x >> 2));      // check vertical |
}

With a decent level of optimization you can really think of w, x, y and z as "aliases" for the shifted values. This means the final return statement throws the entire operation into a big soup for the compiler to play with. On my system this version takes only 65% of the runtime of the original (including the overhead of generating a random position each time). It might win by a larger percentage if the boards are mainly non-winning.

Looking at the disassembly of each (from gcc -O3) the original version is actually shorter, so it's likely the lack of branching in the tight inner loop that really helps.