man-pages/man3/nextafter.3

.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\" Distributed under GPL
.\" Based on glibc infopages
.TH NEXTAFTER 3 2010-09-20 "GNU" "Linux Programmer's Manual"
.SH NAME
nextafter, nextafterf, nextafterl, nexttoward, nexttowardf, nexttowardl \-
floating-point number manipulation
.SH SYNOPSIS
.B #include <math.h>
.sp
.BI "double nextafter(double " x ", double " y );
.br
.BI "float nextafterf(float " x ", float " y );
.br
.BI "long double nextafterl(long double " x ", long double " y );
.sp
.BI "double nexttoward(double " x ", long double " y );
.br
.BI "float nexttowardf(float " x ", long double " y );
.br
.BI "long double nexttowardl(long double " x ", long double " y );
.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 nextafter ():
.RS 4
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED ||
_ISOC99_SOURCE ||
_POSIX_C_SOURCE\ >=\ 200112L;
.br
or
.I cc\ -std=c99
.RE
.br
.BR nextafterf (),
.BR nextafterl ():
.RS 4
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE\ >=\ 200112L;
.br
or
.I cc\ -std=c99
.RE
.br
.BR nexttoward (),
.BR nexttowardf (),
.BR nexttowardl ():
.RS 4
_XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE\ >=\ 200112L;
.br
or
.I cc\ -std=c99
.RE
.ad b
.SH DESCRIPTION
The
.BR nextafter ()
functions return the next representable floating-point value following
.I x
in the direction of
.IR y .
If
.I y
is less than
.IR x ,
these functions will return the largest representable number less than
.IR x .

If \fIx\fP equals \fIy\fP, the functions return \fIy\fP.

The
.BR nexttoward ()
functions do the same as the
.BR nextafter ()
functions, except that they have a
.I "long double"
second argument.
.SH RETURN VALUE
On success,
these functions return the next representable floating-point value after
.I x
in the direction of
.IR y .

If
.I x
equals
.IR y ,
then
.I y
(cast to the same type as
.IR x )
is returned.

If
.I x
or
.I y
is a NaN,
a NaN is returned.

If
.I x
is finite,
.\" e.g., DBL_MAX
and the result would overflow,
a range error occurs,
and the functions return
.BR HUGE_VAL ,
.BR HUGE_VALF ,
or
.BR HUGE_VALL ,
respectively, with the correct mathematical sign.

If
.I x
is not equal to
.IR y ,
and the correct function result would be subnormal, zero, or underflow,
a range error occurs,
and either the correct value (if it can be represented),
or 0.0, is returned.
.SH ERRORS
See
.BR math_error (7)
for information on how to determine whether an error has occurred
when calling these functions.
.PP
The following errors can occur:
.TP
Range error: result overflow
.\" e.g., nextafter(DBL_MAX, HUGE_VAL);
.\" .I errno
.\" is set to
.\" .BR ERANGE .
An overflow floating-point exception
.RB ( FE_OVERFLOW )
is raised.
.TP
Range error: result is subnormal or underflows
.\" e.g., nextafter(DBL_MIN, 0.0);
.\" .I errno
.\" is set to
.\" .BR ERANGE .
An underflow floating-point exception
.RB ( FE_UNDERFLOW )
is raised.
.PP
These functions do not set
.IR errno .
.\" FIXME . Is it intentional that these functions do not set errno?
.\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6799
.SH "CONFORMING TO"
C99, POSIX.1-2001.
This function is defined in IEC 559 (and the appendix with
recommended functions in IEEE 754/IEEE 854).
.SH BUGS
In glibc version 2.5 and earlier, these functions do not raise an underflow
floating-point
.RB ( FE_UNDERFLOW )
exception when an underflow occurs.
.SH "SEE ALSO"
.BR nearbyint (3)