source: trunk/minix/lib/i86/string/strchr.s@ 9

!       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