Mercurial > hg > octave-lojdl > gnulib-hg
annotate lib/cbrtf.c @ 17426:90f3d53e01f5
sig2str: port to C++
* lib/sig2str.h (sig2str, str2sig): Declare as extern "C".
Reported by Daniel J Sebald in
<http://lists.gnu.org/archive/html/bug-gnulib/2013-06/msg00000.html>.
| author | Paul Eggert <eggert@cs.ucla.edu> |
|---|---|
| date | Sun, 02 Jun 2013 11:52:41 -0700 |
| parents | e542fd46ad6f |
| children |
| rev | line source |
|---|---|
| 16534 | 1 /* Compute cubic root of float value. |
|
17249
e542fd46ad6f
maint: update all copyright year number ranges
Eric Blake <eblake@redhat.com>
parents:
16693
diff
changeset
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2 Copyright (C) 1997, 2012-2013 Free Software Foundation, Inc. |
| 16534 | 3 |
| 4 Contributed by Dirk Alboth <dirka@uni-paderborn.de> and | |
| 5 Ulrich Drepper <drepper@cygnus.com>, 1997. | |
| 6 | |
| 7 This program is free software: you can redistribute it and/or modify | |
| 8 it under the terms of the GNU General Public License as published by | |
| 9 the Free Software Foundation; either version 3 of the License, or | |
| 10 (at your option) any later version. | |
| 11 | |
| 12 This program is distributed in the hope that it will be useful, | |
| 13 but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| 14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
| 15 GNU General Public License for more details. | |
| 16 | |
| 17 You should have received a copy of the GNU General Public License | |
| 18 along with this program. If not, see <http://www.gnu.org/licenses/>. */ | |
| 19 | |
| 20 #include <config.h> | |
| 21 | |
| 22 /* Specification. */ | |
| 23 #include <math.h> | |
| 24 | |
|
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Avoid compilation errors with MSVC option -fp:strict.
Bruno Haible <bruno@clisp.org>
parents:
16534
diff
changeset
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25 /* MSVC with option -fp:strict refuses to compile constant initializers that |
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55c4c6aa19f4
Avoid compilation errors with MSVC option -fp:strict.
Bruno Haible <bruno@clisp.org>
parents:
16534
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changeset
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26 contain floating-point operations. Pacify this compiler. */ |
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55c4c6aa19f4
Avoid compilation errors with MSVC option -fp:strict.
Bruno Haible <bruno@clisp.org>
parents:
16534
diff
changeset
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27 #ifdef _MSC_VER |
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55c4c6aa19f4
Avoid compilation errors with MSVC option -fp:strict.
Bruno Haible <bruno@clisp.org>
parents:
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diff
changeset
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28 # pragma fenv_access (off) |
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55c4c6aa19f4
Avoid compilation errors with MSVC option -fp:strict.
Bruno Haible <bruno@clisp.org>
parents:
16534
diff
changeset
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29 #endif |
|
55c4c6aa19f4
Avoid compilation errors with MSVC option -fp:strict.
Bruno Haible <bruno@clisp.org>
parents:
16534
diff
changeset
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30 |
| 16534 | 31 /* Code based on glibc/sysdeps/ieee754/flt-32/s_cbrtf.c. */ |
| 32 | |
| 33 #define CBRT2 1.2599210498948731648 /* 2^(1/3) */ | |
| 34 #define SQR_CBRT2 1.5874010519681994748 /* 2^(2/3) */ | |
| 35 | |
| 36 static const double factor[5] = | |
| 37 { | |
| 38 1.0 / SQR_CBRT2, | |
| 39 1.0 / CBRT2, | |
| 40 1.0, | |
| 41 CBRT2, | |
| 42 SQR_CBRT2 | |
| 43 }; | |
| 44 | |
| 45 | |
| 46 float | |
| 47 cbrtf (float x) | |
| 48 { | |
| 49 if (isfinite (x) && x != 0.0f) | |
| 50 { | |
| 51 float xm, ym, u, t2; | |
| 52 int xe; | |
| 53 | |
| 54 /* Reduce X. XM now is an range 1.0 to 0.5. */ | |
| 55 xm = frexpf (fabsf (x), &xe); | |
| 56 | |
| 57 u = (0.492659620528969547 | |
| 58 + (0.697570460207922770 - 0.191502161678719066 * xm) * xm); | |
| 59 | |
| 60 t2 = u * u * u; | |
| 61 | |
| 62 ym = u * (t2 + 2.0 * xm) / (2.0 * t2 + xm) * factor[2 + xe % 3]; | |
| 63 | |
| 64 return ldexpf (x > 0.0 ? ym : -ym, xe / 3); | |
| 65 } | |
| 66 else | |
| 67 return x + x; | |
| 68 } |