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bzero.S revision 1.4 
      1 /*	$NetBSD: bzero.S,v 1.4 2020/05/05 06:20:55 skrll Exp $	*/
      2 
      3 /*	$OpenBSD: bzero.S,v 1.3 2001/06/04 23:14:02 mickey Exp $	*/
      4 
      5 /*
      6  *  (c) Copyright 1988 HEWLETT-PACKARD COMPANY
      7  *
      8  *  To anyone who acknowledges that this file is provided "AS IS"
      9  *  without any express or implied warranty:
     10  *      permission to use, copy, modify, and distribute this file
     11  *  for any purpose is hereby granted without fee, provided that
     12  *  the above copyright notice and this notice appears in all
     13  *  copies, and that the name of Hewlett-Packard Company not be
     14  *  used in advertising or publicity pertaining to distribution
     15  *  of the software without specific, written prior permission.
     16  *  Hewlett-Packard Company makes no representations about the
     17  *  suitability of this software for any purpose.
     18  */
     19 /*
     20  * Copyright (c) 1990,1994 The University of Utah and
     21  * the Computer Systems Laboratory (CSL).  All rights reserved.
     22  *
     23  * THE UNIVERSITY OF UTAH AND CSL PROVIDE THIS SOFTWARE IN ITS "AS IS"
     24  * CONDITION, AND DISCLAIM ANY LIABILITY OF ANY KIND FOR ANY DAMAGES
     25  * WHATSOEVER RESULTING FROM ITS USE.
     26  *
     27  * CSL requests users of this software to return to csl-dist (at) cs.utah.edu any
     28  * improvements that they make and grant CSL redistribution rights.
     29  *
     30  * 	Utah $Hdr: bzero.s 1.9 94/12/14$
     31  *	Author: Bob Wheeler, University of Utah CSL
     32  */
     33 
     34 #include <machine/asm.h>
     35 
     36 #ifdef SYSLIBC_SCCS
     37 	.text
     38 	.asciz "$OpenBSD: bzero.S,v 1.3 2001/06/04 23:14:02 mickey Exp $"
     39 	.align	4
     40 #endif
     41 
     42 /*
     43  * void
     44  * bzero(dst, count)
     45  *	void *dst;
     46  *	size_t count;
     47  */
     48 LEAF_ENTRY(bzero)
     49         comb,>=,n %r0,%arg1,$bzero_exit
     50 
     51 	/*
     52 	 * If we need to clear less than a word do it a byte at a time
     53 	 */
     54 
     55 	comib,>>,n 4,%arg1,$bzero_bytes
     56 
     57 	/*
     58 	 * Since we are only clearing memory the alignment restrictions
     59 	 * are simplified. Figure out how many "extra" bytes we need to
     60 	 * store with stbys.
     61 	 */
     62 
     63         extru   %arg0,31,2,%t1
     64         add     %arg1,%t1,%arg1
     65 
     66 	/*
     67 	 * We will zero the destination in blocks of 16 bytes as long as we
     68 	 * can and then we'll go to the 4 byte moves.
     69 	 */
     70 
     71 	comib,>>=	15, %arg1, $bzero_word
     72 	addi		-16, %arg1, %arg1
     73 
     74 $bzero_loop_16:
     75         stbys,b,m %r0,4(%arg0)
     76         stwm    %r0,4(%arg0)
     77         stwm    %r0,4(%arg0)
     78         stwm    %r0,4(%arg0)
     79 	comib,<<	15, %arg1, $bzero_loop_16
     80 	 addi		-16, %arg1, %arg1
     81 
     82 	/*
     83 	 * see if there is anything left that needs to be zeroed in a word
     84 	 * move. Since the count was decremented by 16, add 12 to test if
     85 	 * there are any full word moves left to do.
     86 	 */
     87 
     88 $bzero_word:
     89         addib,<,n 12,%arg1,$bzero_cleanup
     90 
     91 $bzero_loop_4:
     92         addib,>= -4,%arg1,$bzero_loop_4
     93          stbys,b,m %r0,4(%arg0)
     94 
     95 	/*
     96 	 * zero the last bytes that may be unaligned on a word boundary
     97 	 */
     98 
     99 $bzero_cleanup:
    100         addib,=,n 4,%arg1,$bzero_exit
    101         add	%arg0,%arg1,%arg0
    102         b       $bzero_exit
    103          stbys,e %r0,0(%arg0)
    104 	b,n	$bzero_exit
    105 
    106 
    107 	/*
    108 	 * zero by bytes
    109 	 */
    110 
    111 $bzero_bytes:
    112         addib,> -1,%arg1,$bzero_bytes
    113          stbs,ma %r0,1(%arg0)
    114 
    115 $bzero_exit:
    116 	bv,n	%r0(%rp)
    117 EXIT(bzero)
    118 
    119 	.end
    120