Mercurial > hg > octave-nkf > gnulib-hg
annotate lib/integer_length.c @ 17907:0a1c2535cad9
euidaccess: Fix Android build
* modules/euidaccess (Depends-on): Add fcntl-h to ensure that
AT_EACCESS gets declared.
| author | Kevin Cernekee <cernekee@google.com> |
|---|---|
| date | Wed, 11 Feb 2015 15:22:54 -0800 |
| parents | ab58d4870664 |
| children |
| rev | line source |
|---|---|
| 15952 | 1 /* integer_length - find most significant bit in an 'unsigned int'. |
| 17848 | 2 Copyright (C) 2011-2015 Free Software Foundation, Inc. |
| 15952 | 3 |
| 4 This program is free software: you can redistribute it and/or modify | |
| 5 it under the terms of the GNU General Public License as published by | |
| 6 the Free Software Foundation; either version 3 of the License, or | |
| 7 (at your option) any later version. | |
| 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 | |
| 14 You should have received a copy of the GNU General Public License | |
| 15 along with this program. If not, see <http://www.gnu.org/licenses/>. */ | |
| 16 | |
| 17 /* Written by Bruno Haible <bruno@clisp.org>, 2011. */ | |
| 18 | |
| 19 #include <config.h> | |
| 20 | |
| 21 /* Specification. */ | |
| 22 #include "integer_length.h" | |
| 23 | |
| 24 #include <limits.h> | |
| 25 | |
| 26 #include "float+.h" | |
| 27 | |
|
16506
fa4e9b981eb4
Avoid compilation errors with MSVC option -fp:strict.
Bruno Haible <bruno@clisp.org>
parents:
16201
diff
changeset
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28 /* MSVC with option -fp:strict refuses to compile constant initializers that |
|
fa4e9b981eb4
Avoid compilation errors with MSVC option -fp:strict.
Bruno Haible <bruno@clisp.org>
parents:
16201
diff
changeset
|
29 contain floating-point operations. Pacify this compiler. */ |
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fa4e9b981eb4
Avoid compilation errors with MSVC option -fp:strict.
Bruno Haible <bruno@clisp.org>
parents:
16201
diff
changeset
|
30 #ifdef _MSC_VER |
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fa4e9b981eb4
Avoid compilation errors with MSVC option -fp:strict.
Bruno Haible <bruno@clisp.org>
parents:
16201
diff
changeset
|
31 # pragma fenv_access (off) |
|
fa4e9b981eb4
Avoid compilation errors with MSVC option -fp:strict.
Bruno Haible <bruno@clisp.org>
parents:
16201
diff
changeset
|
32 #endif |
|
fa4e9b981eb4
Avoid compilation errors with MSVC option -fp:strict.
Bruno Haible <bruno@clisp.org>
parents:
16201
diff
changeset
|
33 |
| 15952 | 34 #define NBITS (sizeof (unsigned int) * CHAR_BIT) |
| 35 | |
| 36 int | |
| 37 integer_length (unsigned int x) | |
| 38 { | |
| 39 #if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) | |
| 40 if (x == 0) | |
| 41 return 0; | |
| 42 else | |
| 43 return NBITS - __builtin_clz (x); | |
| 44 #else | |
| 45 # if defined DBL_EXPBIT0_WORD && defined DBL_EXPBIT0_BIT | |
| 46 if (NBITS <= DBL_MANT_BIT) | |
| 47 { | |
| 48 /* Use 'double' operations. | |
| 49 Assumes an IEEE 754 'double' implementation. */ | |
| 50 # define DBL_EXP_MASK ((DBL_MAX_EXP - DBL_MIN_EXP) | 7) | |
| 51 # define DBL_EXP_BIAS (DBL_EXP_MASK / 2 - 1) | |
| 52 # define NWORDS \ | |
| 53 ((sizeof (double) + sizeof (unsigned int) - 1) / sizeof (unsigned int)) | |
| 54 typedef union { double value; unsigned int word[NWORDS]; } | |
| 55 memory_double; | |
| 56 | |
| 57 if (x == 0) | |
| 58 return 0; | |
| 59 else | |
| 60 { | |
| 61 memory_double m; | |
| 62 unsigned int exponent; | |
| 63 | |
| 64 if (1) | |
| 65 { | |
| 66 /* Use a single integer to floating-point conversion. */ | |
| 67 m.value = x; | |
| 68 } | |
| 69 else | |
| 70 { | |
| 71 /* Use a single floating-point subtraction. */ | |
| 72 /* 2^(DBL_MANT_DIG-1). */ | |
| 73 static const double TWO_DBL_MANT_DIG = | |
| 74 /* Assume DBL_MANT_DIG <= 5 * 31. | |
| 75 Use the identity | |
| 76 n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5). */ | |
| 77 (double) (1U << ((DBL_MANT_DIG - 1) / 5)) | |
| 78 * (double) (1U << ((DBL_MANT_DIG - 1 + 1) / 5)) | |
| 79 * (double) (1U << ((DBL_MANT_DIG - 1 + 2) / 5)) | |
| 80 * (double) (1U << ((DBL_MANT_DIG - 1 + 3) / 5)) | |
| 81 * (double) (1U << ((DBL_MANT_DIG - 1 + 4) / 5)); | |
| 82 | |
| 83 /* Construct 2^(DBL_MANT_DIG-1) + x by hand. */ | |
| 84 m.word[DBL_EXPBIT0_WORD] = | |
| 85 (DBL_MANT_DIG + DBL_EXP_BIAS) << DBL_EXPBIT0_BIT; | |
| 86 m.word[1 - DBL_EXPBIT0_WORD] = x; | |
| 87 | |
| 88 /* Subtract 2^(DBL_MANT_DIG-1). */ | |
| 89 m.value = m.value - TWO_DBL_MANT_DIG; | |
| 90 } | |
| 91 | |
| 92 exponent = | |
| 93 (m.word[DBL_EXPBIT0_WORD] >> DBL_EXPBIT0_BIT) & DBL_EXP_MASK; | |
| 94 return exponent - DBL_EXP_BIAS; | |
| 95 } | |
| 96 } | |
| 97 else | |
| 98 # endif | |
| 99 if (NBITS == 32) | |
| 100 { | |
| 101 /* 6 comparisons. */ | |
| 102 if (x != 0) | |
| 103 { | |
| 104 int result = 1; | |
| 105 if (x >= 0x10000) | |
| 106 { | |
| 107 x = x >> 16; | |
| 108 result += 16; | |
| 109 } | |
| 110 if (x >= 0x100) | |
| 111 { | |
| 112 x = x >> 8; | |
| 113 result += 8; | |
| 114 } | |
| 115 if (x >= 0x10) | |
| 116 { | |
| 117 x = x >> 4; | |
| 118 result += 4; | |
| 119 } | |
| 120 if (x >= 0x4) | |
| 121 { | |
| 122 x = x >> 2; | |
| 123 result += 2; | |
| 124 } | |
| 125 if (x >= 0x2) | |
| 126 { | |
| 127 x = x >> 1; | |
| 128 result += 1; | |
| 129 } | |
| 130 return result; | |
| 131 } | |
| 132 else | |
| 133 return 0; | |
| 134 } | |
| 135 else | |
| 136 { | |
| 137 /* Naive loop. | |
| 138 Works for any value of NBITS. */ | |
| 139 int j; | |
| 140 | |
| 141 for (j = NBITS - 1; j >= 0; j--) | |
| 142 if (x & (1U << j)) | |
| 143 return j + 1; | |
| 144 return 0; | |
| 145 } | |
| 146 #endif | |
| 147 } |