memmove.s

早期freebsd实现

/*-
 * Copyright (c) 1990, 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 "@(#)memmove.s	8.1 (Berkeley) 6/4/93"
#endif /* LIBC_SCCS and not lint */

/*
 * void *memmove(dst, src, size)
 * returns dst
 *
 * This optimises the usual case (count < 65536) at the expense
 * of some extra memory references and branches when count >= 65536.
 */

#include "DEFS.h"

ENTRY(memmove, 0)
	movzwl	$65535,r0	/* r0 = 64K (needed below) */
	movq	8(ap),r1	/* r1 = src, r2 = length */
	movl	4(ap),r3	/* r3 = dst */
	cmpl	r1,r3
	bgtru	1f		/* normal forward case */
	beql	2f		/* equal, nothing to do */
	addl2	r2,r1		/* overlaps iff src<dst but src+len>dst */
	cmpl	r1,r3
	bgtru	4f		/* overlapping, must move backwards */
	subl2	r2,r1

1:	/* move forward */
	cmpl	r2,r0
	bgtru	3f		/* stupid movc3 limitation */
	movc3	r2,(r1),(r3)	/* move it all */
2:
	movl	4(ap),r0	/* return original dst */
	ret
3:
	subl2	r0,12(ap)	/* adjust length by 64K */
	movc3	r0,(r1),(r3)	/* move 64K */
	movl	12(ap),r2
	decw	r0		/* from 0 to 65535 */
	brb	1b		/* retry */

4:	/* move backward */
	addl2	r2,r3
5:
	cmpl	r2,r0
	bgtru	6f		/* stupid movc3 limitation */
	subl2	r2,r1
	subl2	r2,r3
	movc3	r2,(r1),(r3)	/* move it all */
	movl	4(ap),r0	/* return original dst */
	ret
6:
	subl2	r0,12(ap)	/* adjust length by 64K */
	subl2	r0,r1
	subl2	r0,r3
	movc3	r0,(r1),(r3)	/* move 64K */
	movl	12(ap),r2
	decw	r0
	subl2	r0,r1
	subl2	r0,r3
	brb	5b