.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)

.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk

.\"     <mtk.manpages@gmail.com>

.\"

.\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)

.\" Distributed under GPL

.\" %%%LICENSE_END

.\"

.\" Based on glibc infopages

.\"

.TH NEXTAFTER 3 2017-09-15 "GNU" "Linux Programmer's Manual"

.SH NAME

nextafter, nextafterf, nextafterl, nexttoward, nexttowardf, nexttowardl \-

floating-point number manipulation

.SH SYNOPSIS

.B #include <math.h>

.PP

.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 );

.PP

.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 );

.PP

Link with \fI\-lm\fP.

.PP

.in -4n

Feature Test Macro Requirements for glibc (see

.BR feature_test_macros (7)):

.in

.PP

.ad l

.BR nextafter ():

.RS 4

_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L

    || _XOPEN_SOURCE\ >=\ 500

.\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED

    || /* Since glibc 2.19: */ _DEFAULT_SOURCE

    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

.RE

.br

.BR nextafterf (),

.BR nextafterl ():

.RS 4

_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L

    || /* Since glibc 2.19: */ _DEFAULT_SOURCE

    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

.RE

.br

.BR nexttoward (),

.BR nexttowardf (),

.BR nexttowardl ():

.RS 4

_XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||

_POSIX_C_SOURCE\ >=\ 200112L

.RE

.ad b

.SH DESCRIPTION

The

.BR nextafter (),

.BR nextafterf (),

and

.BR nextafterl ()

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 .

.PP

If

.I x

equals

.IR y ,

the functions return

.IR y .

.PP

The

.BR nexttoward (),

.BR nexttowardf (),

and

.BR nexttowardl ()

functions do the same as the corresponding

.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 .

.PP

If

.I x

equals

.IR y ,

then

.I y

(cast to the same type as

.IR x )

is returned.

.PP

If

.I x

or

.I y

is a NaN,

a NaN is returned.

.PP

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.

.PP

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 ATTRIBUTES

For an explanation of the terms used in this section, see

.BR attributes (7).

.TS

allbox;

lbw28 lb lb

l l l.

Interface	Attribute	Value

T{

.BR nextafter (),

.BR nextafterf (),

.br

.BR nextafterl (),

.BR nexttoward (),

.br

.BR nexttowardf (),

.BR nexttowardl ()

T}	Thread safety	MT-Safe

.TE

.SH CONFORMING TO

C99, POSIX.1-2001, POSIX.1-2008.

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)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.