man3/frexp.3

.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
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.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
.\" Modified 2002-07-27 by Walter Harms
.\" 	(walter.harms@informatik.uni-oldenburg.de)
.\"
.TH FREXP 3 2021-03-22 "" "Linux Programmer's Manual"
.SH NAME
frexp, frexpf, frexpl \- convert floating-point number to fractional
and integral components
.SH SYNOPSIS
.nf
.B #include <math.h>
.PP
.BI "double frexp(double " x ", int *" exp );
.BI "float frexpf(float " x ", int *" exp );
.BI "long double frexpl(long double " x ", int *" exp );
.fi
.PP
Link with \fI\-lm\fP.
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR frexpf (),
.BR frexpl ():
.nf
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.SH DESCRIPTION
These functions are used to split the number
.I x
into a
normalized fraction and an exponent which is stored in
.IR exp .
.SH RETURN VALUE
These functions return the normalized fraction.
If the argument
.I x
is not zero,
the normalized fraction is
.I x
times a power of two,
and its absolute value is always in the range 1/2 (inclusive) to
1 (exclusive), that is, [0.5,1).
.PP
If
.I x
is zero, then the normalized fraction is
zero and zero is stored in
.IR exp .
.PP
If
.I x
is a NaN,
a NaN is returned, and the value of
.I *exp
is unspecified.
.PP
If
.I x
is positive infinity (negative infinity),
positive infinity (negative infinity) is returned, and the value of
.I *exp
is unspecified.
.SH ERRORS
No errors occur.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR frexp (),
.BR frexpf (),
.BR frexpl ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.
.PP
The variant returning
.I double
also conforms to
SVr4, 4.3BSD, C89.
.SH EXAMPLES
The program below produces results such as the following:
.PP
.in +4n
.EX
.RB "$" " ./a.out 2560"
frexp(2560, &e) = 0.625: 0.625 * 2\(ha12 = 2560
.RB "$" " ./a.out \-4"
frexp(\-4, &e) = \-0.5: \-0.5 * 2\(ha3 = \-4
.EE
.in
.SS Program source
\&
.EX
#include <math.h>
#include <float.h>
#include <stdio.h>
#include <stdlib.h>

int
main(int argc, char *argv[])
{
    double x, r;
    int exp;

    x = strtod(argv[1], NULL);
    r = frexp(x, &exp);

    printf("frexp(%g, &e) = %g: %g * %d\(ha%d = %g\en",
           x, r, r, FLT_RADIX, exp, x);
    exit(EXIT_SUCCESS);
}
.EE
.SH SEE ALSO
.BR ldexp (3),
.BR modf (3)