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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
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8 .\" Permission is granted to copy and distribute modified versions of this
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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14 .\" manual page may be incorrect or out-of-date.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
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16 .\" the use of the information contained herein. The author(s) may not
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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 2015-04-19 "" "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 .br
63 or
64 .I cc\ -std=c99
65 .RE
66 .ad
67 .SH DESCRIPTION
68 These functions are used to split the number
69 .I x
70 into a
71 normalized fraction and an exponent which is stored in
72 .IR exp .
73 .SH RETURN VALUE
74 These functions return the normalized fraction.
75 If the argument
76 .I x
77 is not zero,
78 the normalized fraction is
79 .I x
80 times a power of two,
81 and its absolute value is always in the range 1/2 (inclusive) to
82 1 (exclusive), that is, [0.5,1).
83
84 If
85 .I x
86 is zero, then the normalized fraction is
87 zero and zero is stored in
88 .IR exp .
89
90 If
91 .I x
92 is a NaN,
93 a NaN is returned, and the value of
94 .I *exp
95 is unspecified.
96
97 If
98 .I x
99 is positive infinity (negative infinity),
100 positive infinity (negative infinity) is returned, and the value of
101 .I *exp
102 is unspecified.
103 .SH ERRORS
104 No errors occur.
105 .SH ATTRIBUTES
106 For an explanation of the terms used in this section, see
107 .BR attributes (7).
108 .TS
109 allbox;
110 lbw27 lb lb
111 l l l.
112 Interface Attribute Value
113 T{
114 .BR frexp (),
115 .BR frexpf (),
116 .BR frexpl ()
117 T} Thread safety MT-Safe
118 .TE
119 .SH CONFORMING TO
120 C99, POSIX.1-2001, POSIX.1-2008.
121
122 The variant returning
123 .I double
124 also conforms to
125 SVr4, 4.3BSD, C89.
126 .SH EXAMPLE
127 The program below produces results such as the following:
128 .sp
129 .nf
130 .in +4n
131 .RB "$" " ./a.out 2560"
132 frexp(2560, &e) = 0.625: 0.625 * 2^12 = 2560
133 .RB "$" " ./a.out \-4"
134 frexp(\-4, &e) = \-0.5: \-0.5 * 2^3 = \-4
135 .in
136 .fi
137 .SS Program source
138 \&
139 .nf
140 #include <math.h>
141 #include <float.h>
142 #include <stdio.h>
143 #include <stdlib.h>
144
145 int
146 main(int argc, char *argv[])
147 {
148 double x, r;
149 int exp;
150
151 x = strtod(argv[1], NULL);
152 r = frexp(x, &exp);
153
154 printf("frexp(%g, &e) = %g: %g * %d^%d = %g\\n",
155 x, r, r, FLT_RADIX, exp, x);
156 exit(EXIT_SUCCESS);
157 }
158 .fi
159 .SH SEE ALSO
160 .BR ldexp (3),
161 .BR modf (3)