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 2015-03-02 "" "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 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
  60 _POSIX_C_SOURCE\ >=\ 200112L;
  61 .br
  62 or
  63 .I cc\ -std=c99
  64 .RE
  65 .ad
  66 .SH DESCRIPTION
  67 The
  68 .BR frexp ()
  69 function is used to split the number
  70 .I x
  71 into a
  72 normalized fraction and an exponent which is stored in
  73 .IR exp .
  74 .SH RETURN VALUE
  75 The
  76 .BR frexp ()
  77 function returns the normalized fraction.
  78 If the argument
  79 .I x
  80 is not zero,
  81 the normalized fraction is
  82 .I x
  83 times a power of two,
  84 and its absolute value is always in the range 1/2 (inclusive) to
  85 1 (exclusive), that is, [0.5,1).
  86
  87 If
  88 .I x
  89 is zero, then the normalized fraction is
  90 zero and zero is stored in
  91 .IR exp .
  92
  93 If
  94 .I x
  95 is a NaN,
  96 a NaN is returned, and the value of
  97 .I *exp
  98 is unspecified.
  99
 100 If
 101 .I x
 102 is positive infinity (negative infinity),
 103 positive infinity (negative infinity) is returned, and the value of
 104 .I *exp
 105 is unspecified.
 106 .SH ERRORS
 107 No errors occur.
 108 .SH ATTRIBUTES
 109 For an explanation of the terms used in this section, see
 110 .BR attributes (7).
 111 .TS
 112 allbox;
 113 lbw27 lb lb
 114 l l l.
 115 Interface       Attribute       Value
 116 T{
 117 .BR frexp (),
 118 .BR frexpf (),
 119 .BR frexpl ()
 120 T}      Thread safety   MT-Safe
 121 .TE
 122 .SH CONFORMING TO
 123 C99, POSIX.1-2001.
 124
 125 The variant returning
 126 .I double
 127 also conforms to
 128 SVr4, 4.3BSD, C89.
 129 .SH EXAMPLE
 130 The program below produces results such as the following:
 131 .sp
 132 .nf
 133 .in +4n
 134 .RB "$" " ./a.out 2560"
 135 frexp(2560, &e) = 0.625: 0.625 * 2^12 = 2560
 136 .RB "$" " ./a.out \-4"
 137 frexp(\-4, &e) = \-0.5: \-0.5 * 2^3 = \-4
 138 .in
 139 .fi
 140 .SS Program source
 141 \&
 142 .nf
 143 #include <math.h>
 144 #include <float.h>
 145 #include <stdio.h>
 146 #include <stdlib.h>
 147
 148 int
 149 main(int argc, char *argv[])
 150 {
 151     double x, r;
 152     int exp;
 153
 154     x = strtod(argv[1], NULL);
 155     r = frexp(x, &exp);
 156
 157     printf("frexp(%g, &e) = %g: %g * %d^%d = %g\\n",
 158            x, r, r, FLT_RADIX, exp, x);
 159     exit(EXIT_SUCCESS);
 160 }
 161 .fi
 162 .SH SEE ALSO
 163 .BR ldexp (3),
 164 .BR modf (3)