/*      $OpenBSD: bzero.S,v 1.5 2015/08/31 02:53:56 guenther Exp $      */
/*      $NetBSD: bzero.S,v 1.2 1996/10/17 03:08:12 cgd Exp $    */

/*
 * Copyright (c) 1995 Carnegie-Mellon University.
 * All rights reserved.
 *
 * Author: Trevor Blackwell
 *
 * Permission to use, copy, modify and distribute this software and
 * its documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * Carnegie Mellon requests users of this software to return to
 *
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie the
 * rights to redistribute these changes.
 */

#include "SYS.h"

LEAF(bzero,2)
        ble     a1,bzero_done
        bic     a1,63,t3        /* t3 is # bytes to do 64 bytes at a time */

        /* If nothing in first word, ignore it */
        subq    zero,a0,t0
        and     t0,7,t0         /* t0 = (0-size)%8 */
        beq     t0,bzero_nostart1

        cmpult  a1,t0,t1        /* if size > size%8 goto noshort */
        beq     t1,bzero_noshort

        /*
         * The whole thing is less than a word.
         * Mask off 1..7 bytes, and finish.
         */
        ldq_u   t2,0(a0)
        lda     t0,-1(zero)     /* t0=-1 */
        mskql   t0,a1,t0        /* Get ff in bytes (a0%8)..((a0+a1-1)%8) */
        insql   t0,a0,t0
        bic     t2,t0,t2        /* zero those bytes in word */
        stq_u   t2,0(a0)
        RET

bzero_noshort:
        /* Handle the first partial word */
        ldq_u   t2,0(a0)
        subq    a1,t0,a1
        mskql   t2,a0,t2        /* zero bytes (a0%8)..7 in word */
        stq_u   t2,0(a0)

        addq    a0,t0,a0        /* round a0 up to next word */
        bic     a1,63,t3        /* recalc t3 (# bytes to do 64 bytes at a
                                   time) */

bzero_nostart1:
        /*
         * Loop, zeroing 64 bytes at a time
         */
        beq     t3,bzero_lp_done
bzero_lp:
        stq     zero,0(a0)
        stq     zero,8(a0)
        stq     zero,16(a0)
        stq     zero,24(a0)
        subq    t3,64,t3
        stq     zero,32(a0)
        stq     zero,40(a0)
        stq     zero,48(a0)
        stq     zero,56(a0)
        addq    a0,64,a0
        bne     t3,bzero_lp

bzero_lp_done:
        /*
         * Handle the last 0..7 words.
         * We mask off the low bits, so we don't need an extra
         * compare instruction for the loop (just a bne. heh-heh)
         */
        and     a1,0x38,t4
        beq     t4,bzero_finish_lp_done
bzero_finish_lp:
        stq     zero,0(a0)
        subq    t4,8,t4
        addq    a0,8,a0
        bne     t4,bzero_finish_lp

        /* Do the last partial word */
bzero_finish_lp_done:
        and     a1,7,t5         /* 0..7 bytes left */
        beq     t5,bzero_done   /* mskqh won't change t0 if t5==0, but I
                                   don't want to touch, say, a new VM page */
        ldq     t0,0(a0)
        mskqh   t0,t5,t0
        stq     t0,0(a0)
bzero_done:
        RET

        END_WEAK(bzero)