1/*        $NetBSD: bzero.S,v 1.1 2005/12/20 19:28:49 christos Exp $   */
2
3/*
4 * Copyright (c) 1995 Carnegie-Mellon University.
5 * All rights reserved.
6 *
7 * Author: Trevor Blackwell
8 *
9 * Permission to use, copy, modify and distribute this software and
10 * its documentation is hereby granted, provided that both the copyright
11 * notice and this permission notice appear in all copies of the
12 * software, derivative works or modified versions, and any portions
13 * thereof, and that both notices appear in supporting documentation.
14 *
15 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
16 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
17 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
18 *
19 * Carnegie Mellon requests users of this software to return to
20 *
21 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
22 *  School of Computer Science
23 *  Carnegie Mellon University
24 *  Pittsburgh PA 15213-3890
25 *
26 * any improvements or extensions that they make and grant Carnegie the
27 * rights to redistribute these changes.
28 */
29
30#include <machine/asm.h>
31
32LEAF(bzero,2)
33          ble       a1,bzero_done
34          bic       a1,63,t3  /* t3 is # bytes to do 64 bytes at a time */
35
36          /* If nothing in first word, ignore it */
37          subq      zero,a0,t0
38          and       t0,7,t0             /* t0 = (0-size)%8 */
39          beq       t0,bzero_nostart1
40
41          cmpult    a1,t0,t1  /* if size > size%8 goto noshort */
42          beq       t1,bzero_noshort
43
44          /*
45           * The whole thing is less than a word.
46           * Mask off 1..7 bytes, and finish.
47           */
48          ldq_u     t2,0(a0)
49          lda       t0,-1(zero)         /* t0=-1 */
50          mskql     t0,a1,t0  /* Get ff in bytes (a0%8)..((a0+a1-1)%8) */
51          insql     t0,a0,t0
52          bic       t2,t0,t2  /* zero those bytes in word */
53          stq_u     t2,0(a0)
54          RET
55
56bzero_noshort:
57          /* Handle the first partial word */
58          ldq_u     t2,0(a0)
59          subq      a1,t0,a1
60          mskql     t2,a0,t2  /* zero bytes (a0%8)..7 in word */
61          stq_u     t2,0(a0)
62
63          addq      a0,t0,a0  /* round a0 up to next word */
64          bic       a1,63,t3  /* recalc t3 (# bytes to do 64 bytes at a
65                                           time) */
66
67bzero_nostart1:
68          /*
69           * Loop, zeroing 64 bytes at a time
70           */
71          beq       t3,bzero_lp_done
72bzero_lp:
73          stq       zero,0(a0)
74          stq       zero,8(a0)
75          stq       zero,16(a0)
76          stq       zero,24(a0)
77          subq      t3,64,t3
78          stq       zero,32(a0)
79          stq       zero,40(a0)
80          stq       zero,48(a0)
81          stq       zero,56(a0)
82          addq      a0,64,a0
83          bne       t3,bzero_lp
84
85bzero_lp_done:
86          /*
87           * Handle the last 0..7 words.
88           * We mask off the low bits, so we don't need an extra
89           * compare instruction for the loop (just a bne. heh-heh)
90           */
91          and       a1,0x38,t4
92          beq       t4,bzero_finish_lp_done
93bzero_finish_lp:
94          stq       zero,0(a0)
95          subq      t4,8,t4
96          addq      a0,8,a0
97          bne       t4,bzero_finish_lp
98
99          /* Do the last partial word */
100bzero_finish_lp_done:
101          and       a1,7,t5             /* 0..7 bytes left */
102          beq       t5,bzero_done       /* mskqh won't change t0 if t5==0, but I
103                                           don't want to touch, say, a new VM page */
104          ldq       t0,0(a0)
105          mskqh     t0,t5,t0
106          stq       t0,0(a0)
107bzero_done:
108          RET
109
110          END(bzero)
111