我希望找到DWORD数组中最重要的非零DWORD。该算法应针对高达128字节的数据大小进行优化。
我已经编写了三个不同的函数,它们都返回特定DWORD的索引。
unsigned long msb_msvc(long* dw, std::intptr_t n)
{
while( --n )
{
if( dw[n] )
break;
}
return n;
}
static inline unsigned long msb_386(long* dw, std::intptr_t n)
{
__asm
{
mov ecx, [dw]
mov eax, [n]
__loop: sub eax, 1
jz SHORT __exit
cmp DWORD PTR [ecx + eax * 4], 0
jz SHORT __loop
__exit:
}
}
static inline unsigned long msb_sse2(long* dw, std::intptr_t n)
{
__asm
{
mov ecx, [dw]
mov eax, [n]
test ecx, 0x0f
jnz SHORT __128_unaligned
__128_aligned:
cmp eax, 4
jb SHORT __64
sub eax, 4
movdqa xmm0, XMMWORD PTR [ecx + eax * 4]
pxor xmm1, xmm1
pcmpeqd xmm0, xmm1
pmovmskb edx, xmm0
not edx
and edx, 0xffff
jz SHORT __128_aligned
jmp SHORT __exit
__128_unaligned:
cmp eax, 4
jb SHORT __64
sub eax, 4
movdqu xmm0, XMMWORD PTR [ecx + eax * 4]
pxor xmm1, xmm1
pcmpeqd xmm0, xmm1
pmovmskb edx, xmm0
not edx
and edx, 0xffff
jz SHORT __128_unaligned
jmp SHORT __exit
__64:
cmp eax, 2
jb __32
sub eax, 2
movq mm0, MMWORD PTR [ecx + eax * 4]
pxor mm1, mm1
pcmpeqd mm0, mm1
pmovmskb edx, mm0
not edx
and edx, 0xff
emms
jz SHORT __64
jmp SHORT __exit
__32:
test eax, eax
jz SHORT __exit
xor eax, eax
jmp __leave ; retn
__exit:
bsr edx, edx
shr edx, 2
add eax, edx
__leave:
}
}
这些函数应该用于预选数据,这些数据将相互比较。因此,它需要具有高性能。
有人知道更好的算法吗?