1/*        $NetBSD: ffs.S,v 1.4 2013/09/12 15:36:14 joerg Exp $        */
2
3/*
4 * Copyright (c) 1992, 1993
5 *        The Regents of the University of California.  All rights reserved.
6 *
7 * This software was developed by the Computer Systems Engineering group
8 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
9 * contributed to Berkeley.
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 * from: Header: ffs.s,v 1.3 92/07/07 00:23:57 torek Exp
36 */
37
38#include <machine/asm.h>
39#if defined(LIBC_SCCS) && !defined(lint)
40#if 0
41          .asciz "@(#)ffs.s   8.1 (Berkeley) 6/4/93"
42#else
43          RCSID("$NetBSD: ffs.S,v 1.4 2013/09/12 15:36:14 joerg Exp $")
44#endif
45#endif  /* LIBC_SCCS and not lint */
46
47/*
48 * ffs returns the number of the rightmost bit set in its argument,
49 * i.e., the lowest value such that (x & (ffs(x) - 1)) is nonzero.
50 * If no bits are set, ffs returns 0.
51 *
52 * We use a table lookup on each byte.
53 *
54 * In each section below, %o1 is the current byte (0, 1, 2, or 3).
55 * The last byte is handled specially: for the first three,
56 * if that byte is nonzero, we return the table value
57 * (plus 0, 8, or 16 for the byte number), but for the last
58 * one, we just return the table value plus 24.  This means
59 * that ffstab[0] must be -24 so that ffs(0) will return 0.
60 */
61WEAK_ALIAS(__ffssi2,ffs)
62ENTRY(ffs)
63#ifdef __PIC__
64          PICCY_SET(ffstab, %o2, %o3)
65#else
66          set       ffstab, %o2
67#endif
68          andcc     %o0, 0xff, %o1      ! get low byte
69          be,a      1f                  ! try again if 0
70           srl      %o0, 8, %o0         ! delay slot, get ready for next byte
71
72          retl                          ! return ffstab[%o1]
73           ldsb     [%o2 + %o1], %o0
74
751:
76          andcc     %o0, 0xff, %o1      ! byte 1 like byte 0...
77          be,a      2f
78           srl      %o0, 8, %o0         ! (use delay to prepare for byte 2)
79
80          ldsb      [%o2 + %o1], %o0
81          retl                          ! return ffstab[%o1] + 8
82           add      %o0, 8, %o0
83
842:
85          andcc     %o0, 0xff, %o1
86          be,a      3f
87           srl      %o0, 8, %o0         ! (prepare for byte 3)
88
89          ldsb      [%o2 + %o1], %o0
90          retl                          ! return ffstab[%o1] + 16
91           add      %o0, 16, %o0
92
933:                                      ! just return ffstab[%o0] + 24
94          ldsb      [%o2 + %o0], %o0
95          retl
96           add      %o0, 24, %o0
97
98ffstab:
99          .byte     -24,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1 /* 00-0f */
100          .byte     5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1         /* 10-1f */
101          .byte     6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1         /* 20-2f */
102          .byte     5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1         /* 30-3f */
103          .byte     7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1         /* 40-4f */
104          .byte     5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1         /* 50-5f */
105          .byte     6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1         /* 60-6f */
106          .byte     5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1         /* 70-7f */
107          .byte     8,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1         /* 80-8f */
108          .byte     5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1         /* 10-9f */
109          .byte     6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1         /* a0-af */
110          .byte     5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1         /* b0-bf */
111          .byte     7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1         /* c0-cf */
112          .byte     5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1         /* d0-df */
113          .byte     6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1         /* e0-ef */
114          .byte     5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1         /* f0-ff */
115