3 ms·
This also has the false dependency problem (using eax as the popcnt destination register three times), and neither one of your VC examples is using the 8 byte p
by minimax 11y ago
This also has the false dependency problem (using eax as the popcnt destination register three times), and neither one of your VC examples is using the 8 byte popcnt instruction.
- corysama 11y agoSwitching to __popcnt64 uses 8 byte popcnt. But, I can't get rid of the false dependency problem. RES64 cnt0=0, cnt1=0, cnt2=0, cnt3=0; SIZE_T ndqwords = len / (sizeof(RES64) * 4); for(; ndqwords; ndqwords--) { cnt0 += __popcnt64(*(RES64*)buf); cnt1 += __popcnt64(*(RES64*)(buf + sizeof(RES64) )); cnt2 += __popcnt64(*(RES64*)(buf + sizeof(RES64) * 2 )); cnt3 += __popcnt64(*(RES64*)(buf + sizeof(RES64) * 3 )); buf += sizeof(RES64) * 4; } cnt = cnt0 + cnt1 + cnt2 + cnt3; 000000013FD61FF3 popcnt rax,qword ptr [rdx] 000000013FD61FF8 add rdx,20h 000000013FD61FFC add r9,rax 000000013FD61FFF popcnt rax,qword ptr [rdx-18h] 000000013FD62005 add r10,rax 000000013FD62008 popcnt rax,qword ptr [rdx-10h] 000000013FD6200E add r8,rax 000000013FD62011 popcnt rax,qword ptr [rdx-8] 000000013FD62017 add r11,rax 000000013FD6201A dec rcx 000000013FD6201D jne main+0C3h (13FD61FF3h)
- corysama 11y agoThis gets rid of the false dependency problem. Not a shining example of simplicity or reliability. But, interesting that it works. struct A { RES64 cnt0; RES64 cnt1; RES64 cnt2; RES64 cnt3; } a; RES64 cnt0=0, cnt1=0, cnt2=0, cnt3=0; SIZE_T ndqwords = len / (sizeof(RES64) * 4); for(; ndqwords; ndqwords--) { a.cnt0 = __popcnt64(*(RES64*)buf); a.cnt1 = __popcnt64(*(RES64*)(buf + sizeof(RES64) )); a.cnt2 = __popcnt64(*(RES64*)(buf + sizeof(RES64) * 2 )); a.cnt3 = __popcnt64(*(RES64*)(buf + sizeof(RES64) * 3 )); cnt0 += a.cnt0; cnt1 += a.cnt1; cnt2 += a.cnt2; cnt3 += a.cnt3; buf += sizeof(RES64) * 4; } cnt = cnt0 + cnt1 + cnt2 + cnt3; 000000013F2320C0 popcnt rax,qword ptr [r8] 000000013F2320C5 popcnt rcx,qword ptr [r8+8] 000000013F2320CB popcnt rdx,qword ptr [r8+10h] 000000013F2320D1 popcnt rbx,qword ptr [r8+18h] 000000013F2320D7 add r11,rax 000000013F2320DA add rdi,rcx 000000013F2320DD add rsi,rdx 000000013F2320E0 add r8,20h 000000013F2320E4 add rbp,rbx 000000013F2320E7 dec r10 000000013F2320EA jne main+0D0h (13F2320C0h)
- bro-stick 11y agoIn writing a fast Hamming distance library in Go, dropping inline popcnt64 in using cgo was far slower than good, old-fashioned lookup table method for a single byte on a Haswell mobile processor. For the uint64 case, bitfolding was still faster than popcnt64. Perhaps for the vector buffer case, popcnt64 is faster.