strncpy.s

早期freebsd实现

/*
 * Copyright (c) 1983, 1993
 *	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 "@(#)strncpy.s	8.1 (Berkeley) 6/4/93"
#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