minix/lib/i86/string/_memmove.s

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2005-04-21 16:53:53 +02:00
! _memmove() Author: Kees J. Bot
! 27 Jan 1994
.sect .text; .sect .rom; .sect .data; .sect .bss
! void *_memmove(void *s1, const void *s2, size_t n)
! Copy a chunk of memory. Handle overlap.
!
.sect .text
.define __memmove, __memcpy
__memmove:
push bp
mov bp, sp
push si
push di
mov di, 4(bp) ! String s1
mov si, 6(bp) ! String s2
mov cx, 8(bp) ! Length
mov ax, di
sub ax, si
cmp ax, cx
jb downwards ! if (s2 - s1) < n then copy downwards
__memcpy:
cld ! Clear direction bit: upwards
cmp cx, #16
jb upbyte ! Don't bother being smart with short arrays
mov ax, si
or ax, di
testb al, #1
jnz upbyte ! Bit 0 set, use byte copy
upword: shr cx, #1
rep movs ! Copy words
adc cx, cx ! One more byte?
upbyte:
rep movsb ! Copy bytes
done: mov ax, 4(bp) ! Absolutely noone cares about this value
pop di
pop si
pop bp
ret
! Handle bad overlap by copying downwards, don't bother to do word copies.
downwards:
std ! Set direction bit: downwards
add si, cx
dec si
add di, cx
dec di
rep movsb ! Copy bytes
cld
jmp done