xref: /titanic_52/usr/src/lib/libc/sparc/gen/strlen.s (revision 9acbbeaf2a1ffe5c14b244867d427714fab43c5c)
1/*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License, Version 1.0 only
6 * (the "License").  You may not use this file except in compliance
7 * with the License.
8 *
9 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
10 * or http://www.opensolaris.org/os/licensing.
11 * See the License for the specific language governing permissions
12 * and limitations under the License.
13 *
14 * When distributing Covered Code, include this CDDL HEADER in each
15 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
16 * If applicable, add the following below this CDDL HEADER, with the
17 * fields enclosed by brackets "[]" replaced with your own identifying
18 * information: Portions Copyright [yyyy] [name of copyright owner]
19 *
20 * CDDL HEADER END
21 */
22/*
23 * Copyright 2003 Sun Microsystems, Inc.  All rights reserved.
24 * Use is subject to license terms.
25 */
26
27
28.ident	"%Z%%M%	%I%	%E% SMI"
29
30	.file	"%M%"
31
32/*
33 * strlen(s)
34 *
35 * Given string s, return length (not including the terminating null).
36 *
37 * Fast assembler language version of the following C-program strlen
38 * which represents the `standard' for the C-library.
39 *
40 *	size_t
41 *	strlen(s)
42 *	register const char *s;
43 *	{
44 *		register const char *s0 = s + 1;
45 *
46 *		while (*s++ != '\0')
47 *			;
48 *		return (s - s0);
49 *	}
50 */
51
52#include <sys/asm_linkage.h>
53#include "synonyms.h"
54
55	! The object of strlen is to, as quickly as possible, find the
56	! null byte.  To this end, we attempt to get our string aligned
57	! and then blast across it using Alan Mycroft's algorithm for
58	! finding null bytes. If we are not aligned, the string is
59	! checked a byte at a time until it is.  Once this occurs,
60	! we can proceed word-wise across it.  Once a word with a
61	! zero byte has been found, we then check the word a byte
62	! at a time until we've located the zero byte, and return
63	! the proper length.
64
65	.align 32
66	ENTRY(strlen)
67	andcc		%o0, 3, %o4	! is src word aligned
68	bz,pt		%icc, .nowalgnd
69	mov		%o0, %o2
70
71	cmp		%o4, 2		! is src half-word aligned
72	be,a,pn		%icc, .s2algn
73	lduh		[%o2], %o1
74
75	ldub		[%o2], %o1
76	tst		%o1		! byte zero?
77	bz,pn		%icc, .done
78	cmp		%o4, 3		! src is byte aligned
79
80	be,pn		%icc, .nowalgnd
81	inc		1, %o2
82
83	lduh		[%o2], %o1
84
85.s2algn:
86	srl		%o1, 8, %o4
87	tst		%o4
88	bz,pn		%icc, .done
89	andcc		%o1, 0xff, %g0
90
91	bz,pn		%icc, .done
92	inc		1, %o2
93
94	inc		1, %o2
95
96.nowalgnd:
97	ld		[%o2], %o1
98	sethi		%hi(0x01010101), %o4
99	sethi		%hi(0x80808080), %o5
100	or		%o4, %lo(0x01010101), %o4
101	or		%o5, %lo(0x80808080), %o5
102
103	andn		%o5, %o1, %o3
104	sub		%o1, %o4, %g1
105	andcc		%o3, %g1, %g0
106	bnz,a,pn	%icc, .nullfound
107	sethi		%hi(0xff000000), %o4
108
109	ld		[%o2+4], %o1
110	inc		4, %o2
111
112.loop:						! this should be aligned to 32
113	inc		4, %o2
114	andn		%o5, %o1, %o3		! %o5 = ~word & 0x80808080
115	sub		%o1, %o4, %g1		! %g1 = word - 0x01010101
116	andcc		%o3, %g1, %g0
117	bz,a,pt		%icc, .loop
118	ld		[%o2], %o1
119
120	dec		4, %o2
121	sethi		%hi(0xff000000), %o4
122.nullfound:
123	andcc		%o1, %o4, %g0
124	bz,pn		%icc, .done		! first byte zero
125	srl		%o4, 8, %o4
126
127	andcc		%o1, %o4, %g0
128	bz,pn		%icc, .done		! second byte zero
129	inc		1, %o2
130
131	srl		%o4, 8, %o4
132	andcc		%o1, %o4, %g0
133	bz,pn		%icc, .done		! thrid byte zero
134	inc		1, %o2
135
136	inc		1, %o2			! fourth byte zero
137.done:
138	retl
139	sub		%o2, %o0, %o0
140	SET_SIZE(strlen)
141
142