1/*        $NetBSD: s_logb.S,v 1.7 2003/08/07 16:44:43 agc Exp $       */
2
3/*-
4 * Copyright (c) 1990 The Regents of the University of California.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * the Systems Programming Group of the University of Utah Computer
9 * Science Department.
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
36#include <machine/asm.h>
37
38;_sccsid:
39;.asciz   "from: @(#)support.s          5.2 (Berkeley) 5/17/90"
40
41RCSID("$NetBSD: s_logb.S,v 1.7 2003/08/07 16:44:43 agc Exp $")
42
43| logb(x)
44| returns the unbiased exponent of x, a signed integer in double precision,
45| except that logb(0) is -INF, logb(INF) is +INF, and logb(NAN) is that NAN.
46ENTRY(logb)
47          movw      %sp@(4),%d0
48          movw      #0x7FF0,%d1         | exponent bits
49          andw      %d1,%d0             | mask off all else
50          cmpw      %d1,%d0             | max exponent?
51          bne       Lfinite             | no, is finite
52          fmoved    %sp@(4),%fp0        | yes, infinite or NaN
53          fbun      Ldone               | NaN returns NaN
54          fabsx     %fp0                | +-inf returns inf
55          jra       Ldone
56Lfinite:
57          fmoved    %sp@(4),%fp0        | get entire number
58          fbne      Lnonz               | zero?
59          flog2x    %fp0                | yes, log(0) a convenient source of -inf
60          jra       Ldone
61Lnonz:
62          fgetexpx %fp0                 | get exponent
63Ldone:
64#ifndef __SVR4_ABI__
65          fmoved    %fp0,%sp@-
66          movel     %sp@+,%d0
67          movel     %sp@+,%d1
68#endif
69          rts
70