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      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 (the "License").
      6  * You may not use this file except in compliance with the License.
      7  *
      8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
      9  * or http://www.opensolaris.org/os/licensing.
     10  * See the License for the specific language governing permissions
     11  * and limitations under the License.
     12  *
     13  * When distributing Covered Code, include this CDDL HEADER in each
     14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
     15  * If applicable, add the following below this CDDL HEADER, with the
     16  * fields enclosed by brackets "[]" replaced with your own identifying
     17  * information: Portions Copyright [yyyy] [name of copyright owner]
     18  *
     19  * CDDL HEADER END
     20  */
     21 
     22 /*
     23  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
     24  * Use is subject to license terms.
     25  */
     26 
     27 	.file	"strlen.s"
     28 
     29 /*
     30  * strlen(s)
     31  *
     32  * Given string s, return length (not including the terminating null).
     33  *
     34  * Fast assembler language version of the following C-program strlen
     35  * which represents the `standard' for the C-library.
     36  *
     37  *	size_t
     38  *	strlen(s)
     39  *	register const char *s;
     40  *	{
     41  *		register const char *s0 = s + 1;
     42  *
     43  *		while (*s++ != '\0')
     44  *			;
     45  *		return (s - s0);
     46  *	}
     47  */
     48 
     49 #include <sys/asm_linkage.h>
     50 
     51 	! The object of strlen is to, as quickly as possible, find the
     52 	! null byte.  To this end, we attempt to get our string aligned
     53 	! and then blast across it using Alan Mycroft's algorithm for
     54 	! finding null bytes. If we are not aligned, the string is
     55 	! checked a byte at a time until it is.  Once this occurs,
     56 	! we can proceed word-wise across it.  Once a word with a
     57 	! zero byte has been found, we then check the word a byte
     58 	! at a time until we've located the zero byte, and return
     59 	! the proper length.
     60 
     61 	.align 32
     62 	ENTRY(strlen)
     63 	andcc		%o0, 3, %o4	! is src word aligned
     64 	bz,pt		%icc, .nowalgnd
     65 	mov		%o0, %o2
     66 
     67 	cmp		%o4, 2		! is src half-word aligned
     68 	be,a,pn		%icc, .s2algn
     69 	lduh		[%o2], %o1
     70 
     71 	ldub		[%o2], %o1
     72 	tst		%o1		! byte zero?
     73 	bz,pn		%icc, .done
     74 	cmp		%o4, 3		! src is byte aligned
     75 
     76 	be,pn		%icc, .nowalgnd
     77 	inc		1, %o2
     78 
     79 	lduh		[%o2], %o1
     80 
     81 .s2algn:
     82 	srl		%o1, 8, %o4
     83 	tst		%o4
     84 	bz,pn		%icc, .done
     85 	andcc		%o1, 0xff, %g0
     86 
     87 	bz,pn		%icc, .done
     88 	inc		1, %o2
     89 
     90 	inc		1, %o2
     91 
     92 .nowalgnd:
     93 	ld		[%o2], %o1
     94 	sethi		%hi(0x01010101), %o4
     95 	sethi		%hi(0x80808080), %o5
     96 	or		%o4, %lo(0x01010101), %o4
     97 	or		%o5, %lo(0x80808080), %o5
     98 
     99 	andn		%o5, %o1, %o3
    100 	sub		%o1, %o4, %g1
    101 	andcc		%o3, %g1, %g0
    102 	bnz,a,pn	%icc, .nullfound
    103 	sethi		%hi(0xff000000), %o4
    104 
    105 	ld		[%o2+4], %o1
    106 	inc		4, %o2
    107 
    108 .loop:						! this should be aligned to 32
    109 	inc		4, %o2
    110 	andn		%o5, %o1, %o3		! %o5 = ~word & 0x80808080
    111 	sub		%o1, %o4, %g1		! %g1 = word - 0x01010101
    112 	andcc		%o3, %g1, %g0
    113 	bz,a,pt		%icc, .loop
    114 	ld		[%o2], %o1
    115 
    116 	dec		4, %o2
    117 	sethi		%hi(0xff000000), %o4
    118 .nullfound:
    119 	andcc		%o1, %o4, %g0
    120 	bz,pn		%icc, .done		! first byte zero
    121 	srl		%o4, 8, %o4
    122 
    123 	andcc		%o1, %o4, %g0
    124 	bz,pn		%icc, .done		! second byte zero
    125 	inc		1, %o2
    126 
    127 	srl		%o4, 8, %o4
    128 	andcc		%o1, %o4, %g0
    129 	bz,pn		%icc, .done		! thrid byte zero
    130 	inc		1, %o2
    131 
    132 	inc		1, %o2			! fourth byte zero
    133 .done:
    134 	retl
    135 	sub		%o2, %o0, %o0
    136 	SET_SIZE(strlen)
    137 
    138