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

/*
 * Copyright (c) 1983 Regents of the University of California.
 * All rights reserved.
 *
 * %sccs.include.redist.c%
 */

#if defined(LIBC_SCCS) && !defined(lint)
        .asciz "@(#)strncpy.s   5.6 (Berkeley) %G%"
#endif /* LIBC_SCCS and not lint */

/*
 * Copy string s2 over top of string s1.
 * Truncate or null-pad to n bytes.
 *
 * char *
 * strncpy(s1, s2, n)
 *      char *s1, *s2;
 */
#include "DEFS.h"

ENTRY(strncpy, R6)
        movl    12(ap),r6       # r6 = n
        bleq    done            # n <= 0
        movl    4(ap),r3        # r3 = s1
        movl    8(ap),r1        # r1 = s2
1:
        movzwl  $65535,r2       # r2 = bytes in first chunk
        cmpl    r6,r2           # r2 = min(bytes in chunk, n);
        jgeq    2f
        movl    r6,r2
2:
        subl2   r2,r6           # update n
        locc    $0,r2,(r1)      # '\0' found?
        jneq    3f
        subl2   r2,r1           # back up pointer updated by locc
        movc3   r2,(r1),(r3)    # copy in next piece
        tstl    r6              # run out of space?
        jneq    1b
        jbr     done
3:                              # copy up to '\0' logic
        addl2   r0,r6           # r6 = number of null-pad bytes
        subl2   r0,r2           # r2 = number of bytes to move
        subl2   r2,r1           # back up pointer updated by locc
        movc3   r2,(r1),(r3)    # copy in last piece
4:                              # null-pad logic
        movzwl  $65535,r2       # r2 = bytes in first chunk
        cmpl    r6,r2           # r2 = min(bytes in chunk, n);
        jgeq    5f
        movl    r6,r2
5:
        subl2   r2,r6           # update n
        movc5   $0,(r3),$0,r2,(r3)# pad with '\0's
        tstl    r6              # finished padding?
        jneq    4b
done:
        movl    4(ap),r0        # return s1
        ret