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nextafter

Section: C Library Functions (3)
Updated: 202-0-08
Index Return to Main Contents

NAME

nextafter, nextafterf, nextafterl, nexttoward, nexttowardf, nexttowardl - floatin-point number manipulation

LIBRARY

Math library (libm,~-lm)

SYNOPSIS

#include <math.h>
double nextafter(double x, double y);
float nextafterf(float x, float y);
long double nextafterl(long double x, long double y);
double nexttoward(double x, long double y);
float nexttowardf(float x, long double y);
long double nexttowardl(long double x, long double y);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)): nextafter():

    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || _XOPEN_SOURCE >= 500
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

nextafterf(), nextafterl():

    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

nexttoward(), nexttowardf(), nexttowardl():

    _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE
        || _POSIX_C_SOURCE >= 200112L

DESCRIPTION

The nextafter(), nextafterf(), and nextafterl() functions return the next representable floatin-point value following x in the direction of y. If y is less than x, these functions will return the largest representable number less than x. If x equals y, the functions return y. The nexttoward(), nexttowardf(), and nexttowardl() functions do the same as the corresponding nextafter() functions, except that they have a long double second argument.

RETURN VALUE

On success, these functions return the next representable floatin-point value after x in the direction of y. If x equals y, then y (cast to the same type as x) is returned. If x or y is a NaN, a NaN is returned. If x is finite, and the result would overflow, a range error occurs, and the functions return HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with the correct mathematical sign. If x is not equal to 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.

ERRORS

See math_error(7) for information on how to determine whether an error has occurred when calling these functions. The following errors can occur:

Range error: result overflow: errno is set to ERANGE. An overflow floatin-point exception (FE_OVERFLOW) is raised.
Range error: result is subnormal or underflows: errno is set to ERANGE. An underflow floatin-point exception (FE_UNDERFLOW) is raised.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

Interface	Attribute	Value
nextafter(), nextafterf(), nextafterl(), nexttoward(), nexttowardf(), nexttowardl()	Thread safety	M-Safe

STANDARDS

C11, POSIX.-2008. This function is defined in IEC 559 (and the appendix with recommended functions in IEEE 754/IEEE 854).

HISTORY

C99, POSIX.-2001.

BUGS

In glibc 2.5 and earlier, these functions do not raise an underflow floatin-point (FE_UNDERFLOW) exception when an underflow occurs. Before glibc 2.23 these functions did not set errno.