1 /* -*- c-basic-offset: 4; indent-tabs-mode: nil -*- */
2 /* ====================================================================
3 * Copyright (c) 2005 Carnegie Mellon University. All rights
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in
15 * the documentation and/or other materials provided with the
18 * This work was supported in part by funding from the Defense Advanced
19 * Research Projects Agency and the National Science Foundation of the
20 * United States of America, and the CMU Sphinx Speech Consortium.
22 * THIS SOFTWARE IS PROVIDED BY CARNEGIE MELLON UNIVERSITY ``AS IS'' AND
23 * ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
24 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
25 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY
26 * NOR ITS EMPLOYEES BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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28 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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30 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
31 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
32 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
34 * ====================================================================
38 * Description: Fast approximate fixed-point logarithms
40 * Author: David Huggins-Daines <dhuggins@cs.cmu.edu>
48 #include "sphinxbase/prim_type.h"
49 #include "sphinxbase/fixpoint.h"
51 #include "fe_internal.h"
53 /* Table of log2(x/64)*(1<<DEFAULT_RADIX) */
54 /* perl -e 'for (0..63) {my $x = 1 + $_/64; print "\t(uint32)(", log($x)/log(2), "*(1<<DEFAULT_RADIX)),\n"}' */
55 static uint32 logtable[] = {
56 (uint32) (0 * (1 << DEFAULT_RADIX)),
57 (uint32) (0.0223678130284545 * (1 << DEFAULT_RADIX)),
58 (uint32) (0.0443941193584534 * (1 << DEFAULT_RADIX)),
59 (uint32) (0.0660891904577724 * (1 << DEFAULT_RADIX)),
60 (uint32) (0.0874628412503394 * (1 << DEFAULT_RADIX)),
61 (uint32) (0.108524456778169 * (1 << DEFAULT_RADIX)),
62 (uint32) (0.129283016944966 * (1 << DEFAULT_RADIX)),
63 (uint32) (0.149747119504682 * (1 << DEFAULT_RADIX)),
64 (uint32) (0.169925001442312 * (1 << DEFAULT_RADIX)),
65 (uint32) (0.189824558880017 * (1 << DEFAULT_RADIX)),
66 (uint32) (0.20945336562895 * (1 << DEFAULT_RADIX)),
67 (uint32) (0.228818690495881 * (1 << DEFAULT_RADIX)),
68 (uint32) (0.247927513443586 * (1 << DEFAULT_RADIX)),
69 (uint32) (0.266786540694901 * (1 << DEFAULT_RADIX)),
70 (uint32) (0.285402218862248 * (1 << DEFAULT_RADIX)),
71 (uint32) (0.303780748177103 * (1 << DEFAULT_RADIX)),
72 (uint32) (0.321928094887362 * (1 << DEFAULT_RADIX)),
73 (uint32) (0.339850002884625 * (1 << DEFAULT_RADIX)),
74 (uint32) (0.357552004618084 * (1 << DEFAULT_RADIX)),
75 (uint32) (0.375039431346925 * (1 << DEFAULT_RADIX)),
76 (uint32) (0.39231742277876 * (1 << DEFAULT_RADIX)),
77 (uint32) (0.409390936137702 * (1 << DEFAULT_RADIX)),
78 (uint32) (0.426264754702098 * (1 << DEFAULT_RADIX)),
79 (uint32) (0.442943495848728 * (1 << DEFAULT_RADIX)),
80 (uint32) (0.459431618637297 * (1 << DEFAULT_RADIX)),
81 (uint32) (0.475733430966398 * (1 << DEFAULT_RADIX)),
82 (uint32) (0.491853096329675 * (1 << DEFAULT_RADIX)),
83 (uint32) (0.507794640198696 * (1 << DEFAULT_RADIX)),
84 (uint32) (0.523561956057013 * (1 << DEFAULT_RADIX)),
85 (uint32) (0.539158811108031 * (1 << DEFAULT_RADIX)),
86 (uint32) (0.554588851677637 * (1 << DEFAULT_RADIX)),
87 (uint32) (0.569855608330948 * (1 << DEFAULT_RADIX)),
88 (uint32) (0.584962500721156 * (1 << DEFAULT_RADIX)),
89 (uint32) (0.599912842187128 * (1 << DEFAULT_RADIX)),
90 (uint32) (0.614709844115208 * (1 << DEFAULT_RADIX)),
91 (uint32) (0.62935662007961 * (1 << DEFAULT_RADIX)),
92 (uint32) (0.643856189774725 * (1 << DEFAULT_RADIX)),
93 (uint32) (0.658211482751795 * (1 << DEFAULT_RADIX)),
94 (uint32) (0.672425341971496 * (1 << DEFAULT_RADIX)),
95 (uint32) (0.686500527183218 * (1 << DEFAULT_RADIX)),
96 (uint32) (0.700439718141092 * (1 << DEFAULT_RADIX)),
97 (uint32) (0.714245517666123 * (1 << DEFAULT_RADIX)),
98 (uint32) (0.727920454563199 * (1 << DEFAULT_RADIX)),
99 (uint32) (0.741466986401147 * (1 << DEFAULT_RADIX)),
100 (uint32) (0.754887502163469 * (1 << DEFAULT_RADIX)),
101 (uint32) (0.768184324776926 * (1 << DEFAULT_RADIX)),
102 (uint32) (0.78135971352466 * (1 << DEFAULT_RADIX)),
103 (uint32) (0.794415866350106 * (1 << DEFAULT_RADIX)),
104 (uint32) (0.807354922057604 * (1 << DEFAULT_RADIX)),
105 (uint32) (0.820178962415188 * (1 << DEFAULT_RADIX)),
106 (uint32) (0.832890014164742 * (1 << DEFAULT_RADIX)),
107 (uint32) (0.845490050944375 * (1 << DEFAULT_RADIX)),
108 (uint32) (0.857980995127572 * (1 << DEFAULT_RADIX)),
109 (uint32) (0.870364719583405 * (1 << DEFAULT_RADIX)),
110 (uint32) (0.882643049361841 * (1 << DEFAULT_RADIX)),
111 (uint32) (0.894817763307944 * (1 << DEFAULT_RADIX)),
112 (uint32) (0.906890595608518 * (1 << DEFAULT_RADIX)),
113 (uint32) (0.918863237274595 * (1 << DEFAULT_RADIX)),
114 (uint32) (0.930737337562886 * (1 << DEFAULT_RADIX)),
115 (uint32) (0.94251450533924 * (1 << DEFAULT_RADIX)),
116 (uint32) (0.954196310386875 * (1 << DEFAULT_RADIX)),
117 (uint32) (0.965784284662087 * (1 << DEFAULT_RADIX)),
118 (uint32) (0.977279923499917 * (1 << DEFAULT_RADIX)),
119 (uint32) (0.988684686772166 * (1 << DEFAULT_RADIX)),
130 /* Get the exponent. */
131 #if defined(__GNUC__) && defined(__i386__)
132 __asm__("bsrl %1, %0\n": "=r"(y): "g"(x):"cc");
134 #elif defined(__ppc__)
135 __asm__("cntlzw %0, %1\n": "=r"(y):"r"(x));
138 #elif ((defined(__ARM_ARCH_5__) || defined(__ARM_ARCH_5T__) || \
139 defined(__ARM_ARCH_5TE__)) && !defined(__thumb__))
140 __asm__("clz %0, %1\n": "=r"(y):"r"(x));
144 for (y = 31; y >= 0; --y) {
151 /* Do a table lookup for the MSB of the mantissa. */
152 x = (x >> 25) & 0x3f;
153 return y + logtable[x];
165 return FIXMUL(y, FIXLN_2);