bzero.s

早期freebsd实现

/*-
 * Copyright (c) 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Ralph Campbell.
 *
 * 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.
 */

#include <machine/machAsmDefs.h>

#if defined(LIBC_SCCS) && !defined(lint)
	ASMSTR("@(#)bzero.s	8.1 (Berkeley) 6/4/93")
#endif /* LIBC_SCCS and not lint */

/* bzero(s1, n) */

LEAF(bzero)
	.set	noreorder
	blt	a1, 12, smallclr	# small amount to clear?
	subu	a3, zero, a0		# compute # bytes to word align address
	and	a3, a3, 3
	beq	a3, zero, 1f		# skip if word aligned
	subu	a1, a1, a3		# subtract from remaining count
	swr	zero, 0(a0)		# clear 1, 2, or 3 bytes to align
	addu	a0, a0, a3
1:
	and	v0, a1, 3		# compute number of words left
	subu	a3, a1, v0
	move	a1, v0
	addu	a3, a3, a0		# compute ending address
2:
	addu	a0, a0, 4		# clear words
	bne	a0, a3, 2b		#   unrolling loop doesnt help
	sw	zero, -4(a0)		#   since we are limited by memory speed
smallclr:
	ble	a1, zero, 2f
	addu	a3, a1, a0		# compute ending address
1:
	addu	a0, a0, 1		# clear bytes
	bne	a0, a3, 1b
	sb	zero, -1(a0)
2:
	j	ra
	nop
END(bzero)