There is a trick involving the carry flag that allows two routines to share the same initial few instructions. Here's an illustration.
stringmatch_A: ;(lpsz,lpsz,count)
db 0Ch ;opcode for OR AL,immed8. This will clear the carry flag.
stringmatch_W: ;(lpUnicodeString,lpUnicodeString,count)
stc
push ebp
mov ebp,esp
push esi
push edi
mov esi,[ebp+8]
mov edi,[ebp+12]
mov ecx,[ebp+16]
jc short unicode
@@: cmpsb
loope @B
jmp short stringmatch_done
unicode:
@@: cmpsw
loope @B
stringmatch_done:
mov eax,0
je short @F ;return eax = 0, 1, or -1 according to the comparison
sbb eax,eax
sbb eax,-1
@@: pop edi
pop esi
pop ebp
ret 12