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 2019-03-06 "" "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 .PP
  41 .BI "double frexp(double " x ", int *" exp );
  42 .BI "float frexpf(float " x ", int *" exp );
  43 .BI "long double frexpl(long double " x ", int *" exp );
  44 .fi
  45 .PP
  46 Link with \fI\-lm\fP.
  47 .PP
  48 .in -4n
  49 Feature Test Macro Requirements for glibc (see
  50 .BR feature_test_macros (7)):
  51 .in
  52 .PP
  53 .ad l
  54 .BR frexpf (),
  55 .BR frexpl ():
  56 .RS 4
  57 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  58     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  59     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  60 .RE
  61 .ad
  62 .SH DESCRIPTION
  63 These functions are used to split the number
  64 .I x
  65 into a
  66 normalized fraction and an exponent which is stored in
  67 .IR exp .
  68 .SH RETURN VALUE
  69 These functions return the normalized fraction.
  70 If the argument
  71 .I x
  72 is not zero,
  73 the normalized fraction is
  74 .I x
  75 times a power of two,
  76 and its absolute value is always in the range 1/2 (inclusive) to
  77 1 (exclusive), that is, [0.5,1).
  78 .PP
  79 If
  80 .I x
  81 is zero, then the normalized fraction is
  82 zero and zero is stored in
  83 .IR exp .
  84 .PP
  85 If
  86 .I x
  87 is a NaN,
  88 a NaN is returned, and the value of
  89 .I *exp
  90 is unspecified.
  91 .PP
  92 If
  93 .I x
  94 is positive infinity (negative infinity),
  95 positive infinity (negative infinity) is returned, and the value of
  96 .I *exp
  97 is unspecified.
  98 .SH ERRORS
  99 No errors occur.
 100 .SH ATTRIBUTES
 101 For an explanation of the terms used in this section, see
 102 .BR attributes (7).
 103 .TS
 104 allbox;
 105 lbw27 lb lb
 106 l l l.
 107 Interface       Attribute       Value
 108 T{
 109 .BR frexp (),
 110 .BR frexpf (),
 111 .BR frexpl ()
 112 T}      Thread safety   MT-Safe
 113 .TE
 114 .SH CONFORMING TO
 115 C99, POSIX.1-2001, POSIX.1-2008.
 116 .PP
 117 The variant returning
 118 .I double
 119 also conforms to
 120 SVr4, 4.3BSD, C89.
 121 .SH EXAMPLE
 122 The program below produces results such as the following:
 123 .PP
 124 .in +4n
 125 .EX
 126 .RB "$" " ./a.out 2560"
 127 frexp(2560, &e) = 0.625: 0.625 * 2^12 = 2560
 128 .RB "$" " ./a.out \-4"
 129 frexp(\-4, &e) = \-0.5: \-0.5 * 2^3 = \-4
 130 .EE
 131 .in
 132 .SS Program source
 133 \&
 134 .EX
 135 #include <math.h>
 136 #include <float.h>
 137 #include <stdio.h>
 138 #include <stdlib.h>
 139
 140 int
 141 main(int argc, char *argv[])
 142 {
 143     double x, r;
 144     int exp;
 145
 146     x = strtod(argv[1], NULL);
 147     r = frexp(x, &exp);
 148
 149     printf("frexp(%g, &e) = %g: %g * %d^%d = %g\en",
 150            x, r, r, FLT_RADIX, exp, x);
 151     exit(EXIT_SUCCESS);
 152 }
 153 .EE
 154 .SH SEE ALSO
 155 .BR ldexp (3),
 156 .BR modf (3)