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Annotation of 43BSDReno/lib/libc/hp300/string/bzero.s, revision 1.1

1.1     ! root        1: /*-
        !             2:  * Copyright (c) 1990 The Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * This code is derived from software contributed to Berkeley by
        !             6:  * the Systems Programming Group of the University of Utah Computer
        !             7:  * Science Department.
        !             8:  *
        !             9:  * Redistribution and use in source and binary forms are permitted
        !            10:  * provided that: (1) source distributions retain this entire copyright
        !            11:  * notice and comment, and (2) distributions including binaries display
        !            12:  * the following acknowledgement:  ``This product includes software
        !            13:  * developed by the University of California, Berkeley and its contributors''
        !            14:  * in the documentation or other materials provided with the distribution
        !            15:  * and in all advertising materials mentioning features or use of this
        !            16:  * software. Neither the name of the University nor the names of its
        !            17:  * contributors may be used to endorse or promote products derived
        !            18:  * from this software without specific prior written permission.
        !            19:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
        !            20:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
        !            21:  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            22:  */
        !            23: 
        !            24: #if defined(LIBC_SCCS) && !defined(lint)
        !            25:        .asciz "@(#)bzero.s     5.1 (Berkeley) 5/12/90"
        !            26: #endif /* LIBC_SCCS and not lint */
        !            27: 
        !            28: #include "DEFS.h"
        !            29: 
        !            30: /*
        !            31:  * This is probably not the best we can do, but it is still much
        !            32:  * faster than the C version in the portable gen directory.
        !            33:  *
        !            34:  * Things that might help:
        !            35:  *     - unroll the longword loop (might not be good for a 68020)
        !            36:  *     - longword, as opposed to word, align when possible (only on the 68020)
        !            37:  *     - use nested DBcc instructions or use one and limit size to 64K
        !            38:  */
        !            39: ENTRY(bzero)
        !            40:        movl    sp@(4),a0       /* destination */
        !            41:        movl    sp@(8),d0       /* count */
        !            42:        jeq     bzdone          /* nothing to do */
        !            43:        movl    a0,d1
        !            44:        btst    #0,d1           /* address odd? */
        !            45:        jeq     bzeven          /* no, skip alignment */
        !            46:        clrb    a0@+            /* yes, clear a byte */
        !            47:        subql   #1,d0           /* adjust count */
        !            48:        jeq     bzdone          /* if zero, all done */
        !            49: bzeven:
        !            50:        movl    d0,d1
        !            51:        lsrl    #2,d1           /* convert to longword count */
        !            52:        jeq     bzbloop         /* no longwords, skip loop */
        !            53: bzlloop:
        !            54:        clrl    a0@+            /* clear a longword */
        !            55:        subql   #1,d1           /* adjust count */
        !            56:        jne     bzlloop         /* still more, keep going */
        !            57:        andl    #3,d0           /* what remains */
        !            58:        jeq     bzdone          /* nothing, all done */
        !            59: bzbloop:
        !            60:        clrb    a0@+            /* clear a byte */
        !            61:        subql   #1,d0           /* adjust count */
        !            62:        jne     bzbloop         /* still more, keep going */
        !            63: bzdone:
        !            64:        rts

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