115 lines
2.2 KiB
ArmAsm
115 lines
2.2 KiB
ArmAsm
/* $NetBSD: strlen.S,v 1.3 1998/04/03 22:58:10 matthias Exp $ */
|
|
|
|
/*
|
|
* Written by Randy Hyde, 1993
|
|
* Public domain.
|
|
*/
|
|
|
|
#include <machine/asm.h>
|
|
|
|
#if defined(LIBC_SCCS)
|
|
RCSID("$NetBSD: strlen.S,v 1.3 1998/04/03 22:58:10 matthias Exp $")
|
|
#endif
|
|
|
|
/*
|
|
* size_t
|
|
* strlen (char *s)
|
|
* compute the length of the string s.
|
|
*/
|
|
|
|
KENTRY(strlen, 4)
|
|
enter [r3,r4],0
|
|
movd B_ARG0,r0
|
|
|
|
/*
|
|
* First begin by seeing if we can doubleword align the
|
|
* pointer. The following code aligns the pointer in r0.
|
|
*/
|
|
|
|
movqd 3,r3
|
|
andd r0,r3
|
|
|
|
0: casew 1f(pc)[r3:w]
|
|
1: .word 5f-0b
|
|
.word 2f-0b
|
|
.word 3f-0b
|
|
.word 4f-0b
|
|
|
|
.align 2,0xa2
|
|
2: cmpqb 0,0(r0) ; beq 7f
|
|
cmpqb 0,1(r0) ; beq 8f
|
|
cmpqb 0,2(r0) ; beq 9f
|
|
addqd 3,r0
|
|
br 5f
|
|
|
|
.align 2,0xa2
|
|
3: cmpqb 0,0(r0) ; beq 7f
|
|
cmpqb 0,1(r0) ; beq 8f
|
|
addqd 2,r0
|
|
br 5f
|
|
|
|
.align 2,0xa2
|
|
4: cmpqb 0,0(r0) ; beq 7f
|
|
addqd 1,r0
|
|
|
|
/*
|
|
* Okay, when we get down here r0 points at a double word
|
|
* algined source block of bytes.
|
|
* This guy processes four bytes at a time and checks for the
|
|
* zero terminating byte amongst the bytes in the double word.
|
|
* This algorithm is de to Dave Rand.
|
|
*
|
|
* Sneaky test for zero amongst four bytes:
|
|
*
|
|
* xxyyzztt
|
|
* -01010101
|
|
* ---------
|
|
* aabbccdd
|
|
* bic xxyyzztt
|
|
* ---------
|
|
* eeffgghh ee=0x80 if xx=0, ff=0x80 if yy=0, etc.
|
|
*
|
|
* This whole result will be zero if there
|
|
* was no zero byte, it will be non-zero if
|
|
* there is a zero byte present.
|
|
*/
|
|
|
|
5: movd 0x01010101,r2 /* Magic number to use */
|
|
movd 0x80808080,r3 /* Another magic number. */
|
|
addqd -4,r0
|
|
|
|
.align 2,0xa2
|
|
0: movd 4(r0),r1 /* Get next double word. */
|
|
addqd 4,r0 /* Advance pointer. */
|
|
movd r1,r4 /* Save for storage later. */
|
|
subd r2,r1 /* Gets borrow if byte = 0. */
|
|
bicd r4,r1 /* Clear original bits. */
|
|
andd r3,r1 /* See if borrow occurred. */
|
|
cmpqd 0,r1
|
|
beq 0b /* See if this DWORD contained a 0. */
|
|
|
|
/*
|
|
* At this point, r0 points at a double word which
|
|
* contains a zero byte. Count the bytes up to the
|
|
* zero.
|
|
*/
|
|
|
|
1: cmpqb 0,0(r0) ; beq 7f
|
|
cmpqb 0,1(r0) ; beq 8f
|
|
cmpqb 0,2(r0) ; beq 9f
|
|
addqd 3,r0 /* Must be in fourth byte. */
|
|
|
|
7: subd B_ARG0,r0
|
|
exit [r3,r4]
|
|
ret ARGS
|
|
|
|
8: addqd 1,r0
|
|
subd B_ARG0,r0
|
|
exit [r3,r4]
|
|
ret ARGS
|
|
|
|
9: addqd 2,r0
|
|
subd B_ARG0,r0
|
|
exit [r3,r4]
|
|
ret ARGS
|