Hi all, The code below is a strlen() procedure implemented in vc7, I tried to understand it but failed. I think the core of this code is its "main_loop", which makes me confused.Can anybody help me? Any hint will be appreciated.Thanks.
public strlen strlen proc .FPO ( 0, 1, 0, 0, 0, 0 ) string equ [esp + 4] mov ecx,string ; ecx -> string test ecx,3 ; test if string is aligned on 32 bits je short main_loop str_misaligned: ; simple byte loop until string is aligned mov al,byte ptr [ecx] add ecx,1 test al,al je short byte_3 test ecx,3 jne short str_misaligned add eax,dword ptr 0 ; 5 byte nop to align label below align 16 ; should be redundant main_loop: mov eax,dword ptr [ecx] ; read 4 bytes mov edx,7efefeffh add edx,eax xor eax,-1 xor eax,edx add ecx,4 test eax,81010100h je short main_loop ; found zero byte in the loop mov eax,[ecx - 4] test al,al ; is it byte 0 je short byte_0 test ah,ah ; is it byte 1 je short byte_1 test eax,00ff0000h ; is it byte 2 je short byte_2 test eax,0ff000000h ; is it byte 3 je short byte_3 jmp short main_loop ; taken if bits 24-30 are clear and bit ; 31 is set byte_3: lea eax,[ecx - 1] mov ecx,string sub eax,ecx ret byte_2: lea eax,[ecx - 2] mov ecx,string sub eax,ecx ret byte_1: lea eax,[ecx - 3] mov ecx,string sub eax,ecx ret byte_0: lea eax,[ecx - 4] mov ecx,string sub eax,ecx ret strlen endp end --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Algorithm Geeks" group. To post to this group, send email to algogeeks@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/algogeeks -~----------~----~----~----~------~----~------~--~---