Annotation of sys/lib/libkern/arch/m68k/bzero.S, Revision 1.1
1.1 ! nbrk 1: /* $OpenBSD: bzero.S,v 1.3 2003/06/02 23:28:08 millert Exp $ */
! 2:
! 3: /*-
! 4: * Copyright (c) 1990 The Regents of the University of California.
! 5: * All rights reserved.
! 6: *
! 7: * This code is derived from software contributed to Berkeley by
! 8: * the Systems Programming Group of the University of Utah Computer
! 9: * Science Department.
! 10: *
! 11: * Redistribution and use in source and binary forms, with or without
! 12: * modification, are permitted provided that the following conditions
! 13: * are met:
! 14: * 1. Redistributions of source code must retain the above copyright
! 15: * notice, this list of conditions and the following disclaimer.
! 16: * 2. Redistributions in binary form must reproduce the above copyright
! 17: * notice, this list of conditions and the following disclaimer in the
! 18: * documentation and/or other materials provided with the distribution.
! 19: * 3. Neither the name of the University nor the names of its contributors
! 20: * may be used to endorse or promote products derived from this software
! 21: * without specific prior written permission.
! 22: *
! 23: * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
! 24: * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
! 25: * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
! 26: * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
! 27: * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
! 28: * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
! 29: * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
! 30: * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
! 31: * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
! 32: * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
! 33: * SUCH DAMAGE.
! 34: */
! 35:
! 36: #if defined(LIBC_SCCS) && !defined(lint)
! 37: .text
! 38: /*.asciz "from: @(#)bzero.s 5.1 (Berkeley) 5/12/90"*/
! 39: .asciz "$OpenBSD: bzero.S,v 1.3 2003/06/02 23:28:08 millert Exp $"
! 40: #endif /* LIBC_SCCS and not lint */
! 41:
! 42: #include "DEFS.h"
! 43:
! 44: /*
! 45: * This is probably not the best we can do, but it is still much
! 46: * faster than the C version in the portable gen directory.
! 47: *
! 48: * Things that might help:
! 49: * - unroll the longword loop (might not be good for a 68020)
! 50: * - longword, as opposed to word, align when possible (only on the 68020)
! 51: * - use nested DBcc instructions or use one and limit size to 64K
! 52: */
! 53: ENTRY(bzero)
! 54: movl sp@(4),a0 | destination
! 55: movl sp@(8),d0 | count
! 56: beq bzdone | nothing to do
! 57: movl a0,d1
! 58: btst #0,d1 | address odd?
! 59: beq bzeven | no, skip alignment
! 60: clrb a0@+ | yes, clear a byte
! 61: subql #1,d0 | adjust count
! 62: beq bzdone | if zero, all done
! 63: bzeven:
! 64: movl d0,d1
! 65: lsrl #2,d1 | convert to longword count
! 66: beq bzbloop | no longwords, skip loop
! 67: bzlloop:
! 68: clrl a0@+ | clear a longword
! 69: subql #1,d1 | adjust count
! 70: bne bzlloop | still more, keep going
! 71: andl #3,d0 | what remains
! 72: beq bzdone | nothing, all done
! 73: bzbloop:
! 74: clrb a0@+ | clear a byte
! 75: subql #1,d0 | adjust count
! 76: bne bzbloop | still more, keep going
! 77: bzdone:
! 78: rts
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