minix/lib/i86/string/strchr.s
2009-11-09 10:26:00 +00:00

38 lines
851 B
ArmAsm

! strchr() Author: Kees J. Bot
! 27 Jan 1994
.sect .text; .sect .rom; .sect .data; .sect .bss
! char *strchr(const char *s, int c)
! Look for a character in a string.
!
.sect .text
.define _strchr
_strchr:
push bp
mov bp, sp
push di
cld
mov di, 4(bp) ! di = string
mov dx, #16 ! Look at small chunks of the string
next: shl dx, #1 ! Chunks become bigger each time
mov cx, dx
xorb al, al ! Look for the zero at the end
repne scasb
pushf ! Remember the flags
sub cx, dx
neg cx ! Some or all of the chunk
sub di, cx ! Step back
movb al, 6(bp) ! The character to look for
repne scasb
je found
popf ! Did we find the end of string earlier?
jne next ! No, try again
xor ax, ax ! Return NULL
pop di
pop bp
ret
found: pop ax ! Get rid of those flags
lea ax, -1(di) ! Address of byte found
pop di
pop bp
ret