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[thirdparty/man-pages.git] / 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 2008-10-29 "" "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>
.sp
.BI "double frexp(double " x ", int *" exp );
.br
.BI "float frexpf(float " x ", int *" exp );
.br
.BI "long double frexpl(long double " x ", int *" exp );
.fi
.sp
Link with \fI\-lm\fP.
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.ad l
.BR frexpf (),
.BR frexpl ():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
.I cc\ -std=c99
.ad b
.SH DESCRIPTION
The
.BR frexp ()
function is used to split the number \fIx\fP into a
normalized fraction and an exponent which is stored in \fIexp\fP.
.SH "RETURN VALUE"
The
.BR frexp ()
function returns the normalized fraction.
If the argument \fIx\fP is not zero,
the normalized fraction is \fIx\fP 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).

If \fIx\fP is zero, then the normalized fraction is
zero and zero is stored in \fIexp\fP.

If
.I x
is a NaN,
a NaN is returned, and the value of
.I *exp
is unspecified.

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 "CONFORMING TO"
C99, POSIX.1-2001.
The variant returning
.I double
also conforms to
SVr4, 4.3BSD, C89.
.SH EXAMPLE
The program below produces results such as the following:
.sp
.nf
.in +4n
.RB "$" " ./a.out 2560"
frexp(2560, &e) = 0.625: 0.625 * 2^12 = 2560
.RB "$" " ./a.out \-4"
frexp(\-4, &e) = \-0.5: \-0.5 * 2^3 = -4
.in
.fi
.SS Program source
.R " "
.nf
#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^%d = %g\\n",
           x, r, r, FLT_RADIX, exp, x);
    exit(EXIT_SUCCESS);
} /* main */
.fi
.SH "SEE ALSO"
.BR ldexp (3),
.BR modf (3)