NetBSD/sys/lib/libkern/arch/ns32k/strlen.S

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/*
* Written by Randy Hyde, 1993
* Public domain.
*/
#include <machine/asm.h>
#if defined(LIBC_SCCS)
RCSID("$NetBSD: strlen.S,v 1.1 1996/11/07 07:36:28 matthias Exp $")
#endif
/*
* size_t
* strlen (char *s)
* compute the length of the string s.
*/
ENTRY(strlen)
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 0
8: addqd 1,r0
subd B_ARG0,r0
exit [r3,r4]
ret 0
9: addqd 2,r0
subd B_ARG0,r0
exit [r3,r4]
ret 0