50 lines
1019 B
NASM
Executable File
50 lines
1019 B
NASM
Executable File
; How string comparison works
|
|
; DI => scasb compares value stored in DI which is 's' with 's' stored in AX register
|
|
; and then increments DI if DF is 0
|
|
; v
|
|
; memory address 1: |s|n|a|t|0|
|
|
; memory address 2: |s|n|a|k|e|0|
|
|
; ^
|
|
; SI => lodsb loads value stored at SI to AX and then increments SI if DF is 0
|
|
os_compare_strings:
|
|
cld
|
|
|
|
.compare:
|
|
lodsb
|
|
scasb ; Compare di to si
|
|
jne .unequal ; If they are not equal, jump to .unequal
|
|
cmp al, 0 ; Check if string is finished
|
|
je .equal ; If it has, return true
|
|
jmp .compare ; Finally, repeat
|
|
|
|
.unequal:
|
|
mov cl, 0 ; Change to 0 if unquality is proven
|
|
ret
|
|
|
|
.equal:
|
|
mov cl, 1
|
|
ret
|
|
|
|
|
|
; Convert a string to all upper case
|
|
os_upper_case:
|
|
pusha
|
|
mov di, si
|
|
.loop:
|
|
lodsb
|
|
inc di
|
|
cmp al, 0
|
|
je .finish
|
|
cmp al, 7Ah
|
|
jns .loop
|
|
cmp al, 61h
|
|
js .loop
|
|
sub al, 20h
|
|
dec di
|
|
stosb
|
|
jmp .loop
|
|
.finish:
|
|
popa
|
|
ret
|
|
|