nextafter(3)

NAME#

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

LIBRARY#

Math library (libm, -lm)

SYNOPSIS#

#include <math.h>

double nextafter(double \nx\n, double \ny\n);\n
\nfloat nextafterf(float \nx\n, float \ny\n);\n
\nlong double nextafterl(long double \nx\n, long double \ny\n);

double nexttoward(double \nx\n, long double \ny\n);\n
\nfloat nexttowardf(float \nx\n, long double \ny\n);\n
\nlong double nexttowardl(long double \nx\n, long double \ny\n);

nextafter():

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

nextafterf(), nextafterl():

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

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

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

DESCRIPTION#

The nextafter(), nextafterf(), and nextafterl() functions return the next representable floating-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 floating-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 floating-point exception (FE_OVERFLOW) is raised.

Range error: result is subnormal or underflows

errno is set to ERANGE. An underflow floating-point exception (FE_UNDERFLOW) is raised.

ATTRIBUTES#

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

STANDARDS#

C11, POSIX.1-2008.

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

HISTORY#

C99, POSIX.1-2001.

BUGS#

In glibc 2.5 and earlier, these functions do not raise an underflow floating-point (FE_UNDERFLOW) exception when an underflow occurs.

Before glibc 2.23 these functions did not set errno.

SEE ALSO#

nearbyint(3)