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annotate lib/logb.c @ 17426:90f3d53e01f5

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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
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children
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1 /* Floating-point exponent.
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2 Copyright (C) 2012-2013 Free Software Foundation, Inc.
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3
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4 This program is free software: you can redistribute it and/or modify
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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.
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8
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9 This program is distributed in the hope that it will be useful,
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10 but WITHOUT ANY WARRANTY; without even the implied warranty of
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11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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12 GNU General Public License for more details.
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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/>. */
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16
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17 #if ! (defined USE_LONG_DOUBLE || defined USE_FLOAT)
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18 # include <config.h>
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19 #endif
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20
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21 /* Specification. */
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22 #include <math.h>
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23
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24 #ifdef USE_LONG_DOUBLE
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25 # define LOGB logbl
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26 # define DOUBLE long double
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27 # define L_(literal) literal##L
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28 # define HUGEVAL HUGE_VALL
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29 # define FREXP frexpl
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30 # define ISNAN isnanl
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31 #elif ! defined USE_FLOAT
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32 # define LOGB logb
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33 # define DOUBLE double
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34 # define L_(literal) literal
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35 # define HUGEVAL HUGE_VAL
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36 # define FREXP frexp
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37 # define ISNAN isnand
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38 #else /* defined USE_FLOAT */
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39 # define LOGB logbf
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40 # define DOUBLE float
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41 # define L_(literal) literal##f
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42 # define HUGEVAL HUGE_VALF
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43 # define FREXP frexpf
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44 # define ISNAN isnanf
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45 #endif
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46
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47 DOUBLE
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48 LOGB (DOUBLE x)
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49 {
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50 if (isfinite (x))
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51 {
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52 if (x == L_(0.0))
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53 /* Return -Infinity. */
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54 return - HUGEVAL;
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55 else
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56 {
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57 int e;
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58
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59 (void) FREXP (x, &e);
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60 return (DOUBLE) (e - 1);
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61 }
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62 }
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63 else
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64 {
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65 if (ISNAN (x))
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66 return x; /* NaN */
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67 else
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68 /* Return +Infinity. */
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69 return HUGEVAL;
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70 }
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71 }