usr/src/lib/libc/vax/string/strstr.s

/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#if defined(LIBC_SCCS) && !defined(lint)
        .asciz "@(#)strstr.s    5.2 (Berkeley) 8/21/90"
#endif /* LIBC_SCCS and not lint */

/*
 * Find the first occurrence of s2 as a substring in s1.
 * If s2 is empty, return s1.
 *
 * char *strstr(s1, s2)
 *      const char *s1, *s2;
 */
#include "DEFS.h"

ENTRY(strstr, 0)
        movq    4(ap),r3        /* r3 = s1, r4 = s2 */
        movzwl  $65535,r2       /* r2 = locc/matchc limit */
        locc    $0,r2,(r4)      /* find '\0' in s2 */
        beql    4f
        subl3   r4,r1,r5        /* r5 = strlen(s2) */
        beql    1f              /* if r5 == 0, return s1 */

        /*
         * s2 is short enough to apply matchc.
         * If s1 is long, we have to do it in stages.
         */
0:      locc    $0,r2,(r3)      /* find '\0' in s1 */
        beql    3f

        /*
         * Both strings are `short'; we can use matchc directly.
         */
        subl3   r3,r1,r1        /* r1 = strlen(s1) */
        matchc  r5,(r4),r1,(r3) /* find substring */
        bneq    2f

        /*
         * r3 points r5 bytes past match.  Return the match.
         */
1:      subl3   r5,r3,r0        /* return (byte_past_match - strlen(s2)) */
        ret

        /*
         * There is no matching substring.
         */
2:      clrl    r0              /* return NULL */
        ret

        /*
         * s1 is too long (> 65535 bytes) to apply matchc directly,
         * but s2 is short enough.  Apply s2 to s1, then (if not
         * found yet) advancing s1 by (65536-strlen(s2)) bytes and
         * loop.
         */
3:      matchc  r5,(r4),r2,(r3) /* search */
        beql    1b              /* if found, go return it */
        decw    r2              /* from 0 to 65535 */
        incl    r3              /* already advanced 65535, now 65536 */
        subl2   r5,r3           /* ... minus strlen(s2) */
        brb     0b

        /*
         * s2 is too long (> 65535 bytes) to bother with matchc.
         */
4:      locc    $0,r2,(r1)      /* continue working on strlen(s2) */
        beql    4b
        subl3   r1,r4,r5        /* r5 = strlen(s2) */
        movb    (r4)+,r2        /* r2 = *s2++ */
        decl    r5              /* fix up length */
5:      movb    (r3)+,r0        /* r0 = *s1++ */
        beql    2b              /* if '\0', return NULL */
        cmpb    r0,r2
        bneq    5b              /* loop until first char found */
        pushr   R5|R4|R3|R2     /* save c, s1, s2, n */
        pushr   R5|R4|R3        /* strncmp(s1, s2, n) */
        calls   $3,_strncmp
        popr    R2|R3|R4|R5     /* restore */
        tstl    r0
        bneq    5b              /* loop until strncmp says rest same too */
        subl3   $1,r3,r0        /* return previous s1 */
        ret