man3/frexp.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\"
   3 .\" %%%LICENSE_START(VERBATIM)
   4 .\" Permission is granted to make and distribute verbatim copies of this
   5 .\" manual provided the copyright notice and this permission notice are
   6 .\" preserved on all copies.
   7 .\"
   8 .\" Permission is granted to copy and distribute modified versions of this
   9 .\" manual under the conditions for verbatim copying, provided that the
  10 .\" entire resulting derived work is distributed under the terms of a
  11 .\" permission notice identical to this one.
  12 .\"
  13 .\" Since the Linux kernel and libraries are constantly changing, this
  14 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  15 .\" responsibility for errors or omissions, or for damages resulting from
  16 .\" the use of the information contained herein.  The author(s) may not
  17 .\" have taken the same level of care in the production of this manual,
  18 .\" which is licensed free of charge, as they might when working
  19 .\" professionally.
  20 .\"
  21 .\" Formatted or processed versions of this manual, if unaccompanied by
  22 .\" the source, must acknowledge the copyright and authors of this work.
  23 .\" %%%LICENSE_END
  24 .\"
  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 These functions are used to split the number
  68 .I x
  69 into a
  70 normalized fraction and an exponent which is stored in
  71 .IR exp .
  72 .SH RETURN VALUE
  73 These functions return the normalized fraction.
  74 If the argument
  75 .I x
  76 is not zero,
  77 the normalized fraction is
  78 .I x
  79 times a power of two,
  80 and its absolute value is always in the range 1/2 (inclusive) to
  81 1 (exclusive), that is, [0.5,1).
  82
  83 If
  84 .I x
  85 is zero, then the normalized fraction is
  86 zero and zero is stored in
  87 .IR exp .
  88
  89 If
  90 .I x
  91 is a NaN,
  92 a NaN is returned, and the value of
  93 .I *exp
  94 is unspecified.
  95
  96 If
  97 .I x
  98 is positive infinity (negative infinity),
  99 positive infinity (negative infinity) is returned, and the value of
 100 .I *exp
 101 is unspecified.
 102 .SH ERRORS
 103 No errors occur.
 104 .SH ATTRIBUTES
 105 For an explanation of the terms used in this section, see
 106 .BR attributes (7).
 107 .TS
 108 allbox;
 109 lbw27 lb lb
 110 l l l.
 111 Interface       Attribute       Value
 112 T{
 113 .BR frexp (),
 114 .BR frexpf (),
 115 .BR frexpl ()
 116 T}      Thread safety   MT-Safe
 117 .TE
 118 .SH CONFORMING TO
 119 C99, POSIX.1-2001, POSIX.1-2008.
 120
 121 The variant returning
 122 .I double
 123 also conforms to
 124 SVr4, 4.3BSD, C89.
 125 .SH EXAMPLE
 126 The program below produces results such as the following:
 127 .sp
 128 .nf
 129 .in +4n
 130 .RB "$" " ./a.out 2560"
 131 frexp(2560, &e) = 0.625: 0.625 * 2^12 = 2560
 132 .RB "$" " ./a.out \-4"
 133 frexp(\-4, &e) = \-0.5: \-0.5 * 2^3 = \-4
 134 .in
 135 .fi
 136 .SS Program source
 137 \&
 138 .nf
 139 #include <math.h>
 140 #include <float.h>
 141 #include <stdio.h>
 142 #include <stdlib.h>
 143
 144 int
 145 main(int argc, char *argv[])
 146 {
 147     double x, r;
 148     int exp;
 149
 150     x = strtod(argv[1], NULL);
 151     r = frexp(x, &exp);
 152
 153     printf("frexp(%g, &e) = %g: %g * %d^%d = %g\\n",
 154            x, r, r, FLT_RADIX, exp, x);
 155     exit(EXIT_SUCCESS);
 156 }
 157 .fi
 158 .SH SEE ALSO
 159 .BR ldexp (3),
 160 .BR modf (3)