Mercurial > hg > octave-jordi > gnulib-hg
annotate lib/floor.c @ 18070:d460ec17f09f
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| author | Karl Berry <karl@freefriends.org> |
|---|---|
| date | Tue, 28 Jul 2015 13:57:32 -0700 |
| parents | ab58d4870664 |
| children |
| rev | line source |
|---|---|
| 9291 | 1 /* Round towards negative infinity. |
| 17848 | 2 Copyright (C) 2007, 2010-2015 Free Software Foundation, Inc. |
| 9291 | 3 |
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Change copyright notice from GPLv2+ to GPLv3+.
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4 This program is free software: you can redistribute it and/or modify |
| 9291 | 5 it under the terms of the GNU General Public License as published by |
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6 the Free Software Foundation; either version 3 of the License, or |
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7 (at your option) any later version. |
| 9291 | 8 |
| 9 This program is distributed in the hope that it will be useful, | |
| 10 but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| 11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
| 12 GNU General Public License for more details. | |
| 13 | |
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14 You should have received a copy of the GNU General Public License |
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15 along with this program. If not, see <http://www.gnu.org/licenses/>. */ |
| 9291 | 16 |
| 17 /* Written by Bruno Haible <bruno@clisp.org>, 2007. */ | |
| 18 | |
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19 #if ! defined USE_LONG_DOUBLE |
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20 # include <config.h> |
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21 #endif |
| 9291 | 22 |
| 23 /* Specification. */ | |
| 24 #include <math.h> | |
| 25 | |
| 26 #include <float.h> | |
| 27 | |
| 28 #ifdef USE_LONG_DOUBLE | |
| 29 # define FUNC floorl | |
| 30 # define DOUBLE long double | |
| 31 # define MANT_DIG LDBL_MANT_DIG | |
| 32 # define L_(literal) literal##L | |
| 33 #elif ! defined USE_FLOAT | |
| 34 # define FUNC floor | |
| 35 # define DOUBLE double | |
| 36 # define MANT_DIG DBL_MANT_DIG | |
| 37 # define L_(literal) literal | |
| 38 #else /* defined USE_FLOAT */ | |
| 39 # define FUNC floorf | |
| 40 # define DOUBLE float | |
| 41 # define MANT_DIG FLT_MANT_DIG | |
| 42 # define L_(literal) literal##f | |
| 43 #endif | |
| 44 | |
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45 /* MSVC with option -fp:strict refuses to compile constant initializers that |
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46 contain floating-point operations. Pacify this compiler. */ |
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47 #ifdef _MSC_VER |
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48 # pragma fenv_access (off) |
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49 #endif |
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50 |
| 9291 | 51 /* 2^(MANT_DIG-1). */ |
| 9313 | 52 static const DOUBLE TWO_MANT_DIG = |
| 9291 | 53 /* Assume MANT_DIG <= 5 * 31. |
| 54 Use the identity | |
| 55 n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5). */ | |
| 56 (DOUBLE) (1U << ((MANT_DIG - 1) / 5)) | |
| 57 * (DOUBLE) (1U << ((MANT_DIG - 1 + 1) / 5)) | |
| 58 * (DOUBLE) (1U << ((MANT_DIG - 1 + 2) / 5)) | |
| 59 * (DOUBLE) (1U << ((MANT_DIG - 1 + 3) / 5)) | |
| 60 * (DOUBLE) (1U << ((MANT_DIG - 1 + 4) / 5)); | |
| 61 | |
| 62 DOUBLE | |
| 63 FUNC (DOUBLE x) | |
| 64 { | |
| 65 /* The use of 'volatile' guarantees that excess precision bits are dropped | |
| 66 at each addition step and before the following comparison at the caller's | |
| 67 site. It is necessary on x86 systems where double-floats are not IEEE | |
| 68 compliant by default, to avoid that the results become platform and compiler | |
| 69 option dependent. 'volatile' is a portable alternative to gcc's | |
| 70 -ffloat-store option. */ | |
| 71 volatile DOUBLE y = x; | |
| 72 volatile DOUBLE z = y; | |
| 73 | |
| 74 if (z > L_(0.0)) | |
| 75 { | |
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76 /* For 0 < x < 1, return +0.0 even if the current rounding mode is |
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77 FE_DOWNWARD. */ |
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78 if (z < L_(1.0)) |
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79 z = L_(0.0); |
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80 /* Avoid rounding errors for values near 2^k, where k >= MANT_DIG-1. */ |
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81 else if (z < TWO_MANT_DIG) |
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82 { |
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83 /* Round to the next integer (nearest or up or down, doesn't matter). */ |
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84 z += TWO_MANT_DIG; |
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85 z -= TWO_MANT_DIG; |
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86 /* Enforce rounding down. */ |
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87 if (z > y) |
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88 z -= L_(1.0); |
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89 } |
| 9291 | 90 } |
| 91 else if (z < L_(0.0)) | |
| 92 { | |
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93 /* Avoid rounding errors for values near -2^k, where k >= MANT_DIG-1. */ |
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94 if (z > - TWO_MANT_DIG) |
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95 { |
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96 /* Round to the next integer (nearest or up or down, doesn't matter). */ |
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97 z -= TWO_MANT_DIG; |
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98 z += TWO_MANT_DIG; |
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99 /* Enforce rounding down. */ |
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100 if (z > y) |
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101 z -= L_(1.0); |
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102 } |
| 9291 | 103 } |
| 104 return z; | |
| 105 } |