man3/frexp.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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  25 .\" References consulted:
  26 .\"     Linux libc source code
  27 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  28 .\"     386BSD man pages
  29 .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
  30 .\" Modified 2002-07-27 by Walter Harms
  31 .\"     (walter.harms@informatik.uni-oldenburg.de)
  32 .\"
  33 .TH FREXP 3 2016-03-15 "" "Linux Programmer's Manual"
  34 .SH NAME
  35 frexp, frexpf, frexpl \- convert floating-point number to fractional
  36 and integral components
  37 .SH SYNOPSIS
  38 .nf
  39 .B #include <math.h>
  40 .sp
  41 .BI "double frexp(double " x ", int *" exp );
  42 .br
  43 .BI "float frexpf(float " x ", int *" exp );
  44 .br
  45 .BI "long double frexpl(long double " x ", int *" exp );
  46 .fi
  47 .sp
  48 Link with \fI\-lm\fP.
  49 .sp
  50 .in -4n
  51 Feature Test Macro Requirements for glibc (see
  52 .BR feature_test_macros (7)):
  53 .in
  54 .sp
  55 .ad l
  56 .BR frexpf (),
  57 .BR frexpl ():
  58 .RS 4
  59 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  60     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  61     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  62 .RE
  63 .ad
  64 .SH DESCRIPTION
  65 These functions are used to split the number
  66 .I x
  67 into a
  68 normalized fraction and an exponent which is stored in
  69 .IR exp .
  70 .SH RETURN VALUE
  71 These functions return the normalized fraction.
  72 If the argument
  73 .I x
  74 is not zero,
  75 the normalized fraction is
  76 .I x
  77 times a power of two,
  78 and its absolute value is always in the range 1/2 (inclusive) to
  79 1 (exclusive), that is, [0.5,1).
  80
  81 If
  82 .I x
  83 is zero, then the normalized fraction is
  84 zero and zero is stored in
  85 .IR exp .
  86
  87 If
  88 .I x
  89 is a NaN,
  90 a NaN is returned, and the value of
  91 .I *exp
  92 is unspecified.
  93
  94 If
  95 .I x
  96 is positive infinity (negative infinity),
  97 positive infinity (negative infinity) is returned, and the value of
  98 .I *exp
  99 is unspecified.
 100 .SH ERRORS
 101 No errors occur.
 102 .SH ATTRIBUTES
 103 For an explanation of the terms used in this section, see
 104 .BR attributes (7).
 105 .TS
 106 allbox;
 107 lbw27 lb lb
 108 l l l.
 109 Interface       Attribute       Value
 110 T{
 111 .BR frexp (),
 112 .BR frexpf (),
 113 .BR frexpl ()
 114 T}      Thread safety   MT-Safe
 115 .TE
 116 .SH CONFORMING TO
 117 C99, POSIX.1-2001, POSIX.1-2008.
 118
 119 The variant returning
 120 .I double
 121 also conforms to
 122 SVr4, 4.3BSD, C89.
 123 .SH EXAMPLE
 124 The program below produces results such as the following:
 125 .sp
 126 .nf
 127 .in +4n
 128 .RB "$" " ./a.out 2560"
 129 frexp(2560, &e) = 0.625: 0.625 * 2^12 = 2560
 130 .RB "$" " ./a.out \-4"
 131 frexp(\-4, &e) = \-0.5: \-0.5 * 2^3 = \-4
 132 .in
 133 .fi
 134 .SS Program source
 135 \&
 136 .nf
 137 #include <math.h>
 138 #include <float.h>
 139 #include <stdio.h>
 140 #include <stdlib.h>
 141
 142 int
 143 main(int argc, char *argv[])
 144 {
 145     double x, r;
 146     int exp;
 147
 148     x = strtod(argv[1], NULL);
 149     r = frexp(x, &exp);
 150
 151     printf("frexp(%g, &e) = %g: %g * %d^%d = %g\\n",
 152            x, r, r, FLT_RADIX, exp, x);
 153     exit(EXIT_SUCCESS);
 154 }
 155 .fi
 156 .SH SEE ALSO
 157 .BR ldexp (3),
 158 .BR modf (3)