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

/*
 * Copyright (c) 1988 Regents of the University of California.
 * All rights reserved.
 *
 * %sccs.include.redist.c%
 */

#if defined(LIBC_SCCS) && !defined(lint)
        .asciz "@(#)strrchr.s   5.4 (Berkeley) %G%"
#endif /* LIBC_SCCS and not lint */

/*
 * Find the last occurence of c in the string cp.
 * Return pointer to match or null pointer.
 *
 * char *
 * strrchr(cp, c)
 *      char *cp, c;
 */
#include "DEFS.h"

        .lcomm  tbl,256

ENTRY(strrchr, 0)
        movzwl  $65535,r4       /* handy 65535 */
        movq    4(ap),r1        /* r1 = cp; r2 = c */
        movzbl  r2,r2
        beql    Lzero           /* special case for c == '\0' */

        clrl    r5              /* r5 = pointer to last match */

/*
 * Fancy scanc version.  Alas, it is not reentrant.
 */
        movab   tbl,r3          /* r3 = address of table */
        bbss    $0,(r3),Lreent  /* ensure not reentering */
        movab   (r3)[r2],r4
        incb    (r4)            /* mark both '\0' and c */
0:
        scanc   $65535,(r1),(r3),$1     /* look for c or '\0' */
        beql    0b              /* keep looking */
        tstb    (r1)
        beql    1f              /* done if '\0' */
        movab   (r1)+,r5        /* save most recently found, and skip over it */
        jbr     0b              /* keep looking */
1:
        movl    r5,r0           /* return last found (if any) */
        clrb    (r4)            /* clean up table */
        clrb    (r3)
        ret

/*
 * Special case for \0.
 */
Lzero:
        locc    $0,r4,(r1)      /* just find end of string */
        beql    Lzero           /* still looking */
        movl    r1,r0           /* found it */
        ret

/*
 * Slower reentrant version is two two-step searches.  The first
 * phase runs until we know where the string ends; it locates any
 * occurrences of c within a 65535-byte block.  Once we have found
 * the end of the string, we find any further occurrences before
 * that location.
 */
Lreent:
0:      /* first phase */
        movl    r1,r3
        locc    $0,r4,(r3)      /* look for '\0' */
        bneq    1f
        locc    r2,r4,(r3)      /* continue phase 1 search for c */
        beql    0b
        movab   (r1)+,r5        /* found c: save and increment pointer */
        brb     0b              /* and continue */

1:      /* second phase */
        subl3   r3,r1,r0        /* length of short block */
        movl    r3,r1
2:
        locc    r2,r0,(r1)      /* look for c */
        beql    3f              /* skip if not found */
        movab   (r1)+,r5        /* save pointer as before */
        sobgtr  r0,2b           /* adjust count and loop */
3:
        movl    r5,r0           /* return stashed pointer */
        ret