nextup, nextupf, nextupl, nextdown, nextdownf, nextdownl — return next floating-point number toward positive/negative infinity


#define _GNU_SOURCE     /* See feature_test_macros(7) */
#include <math.h>

double nextup(double x);
float nextupf(float x);
long double nextupl(long double x);

double nextdown(double x);
float nextdownf(float x);
long double nextdownl(long double x);

Link with -lm.


The nextup(), nextupf(), and nextupl() functions return the next representable floating-point number greater than x.

If x is the smallest representable negative number in the corresponding type, these functions return -0. If x is 0, the returned value is the smallest representable positive number of the corresponding type.

If x is positive infinity, the returned value is positive infinity. If x is negative infinity, the returned value is the largest representable finite negative number of the corresponding type.

If x is Nan, the returned value is NaN.

The value returned by nextdown(x) is -nextup(-x), and similarly for the other types.

Return Value

See Description.


These functions first appeared in glibc in version 2.24.


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

Interface Attribute Value
nextup(), nextupf(), nextupl(),
nextdown(), nextdownf(), nextdownl()
Thread safety MT-Safe

Conforming to

These functions are described in IEEE Std 754-2008 - Standard for Floating-Point Arithmetic and ISO/IEC TS 18661.

See Also

nearbyint(3), nextafter(3)


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Referenced By

The man pages nextdown(3), nextdownf(3), nextdownl(3), nextupf(3) and nextupl(3) are aliases of nextup(3).

2017-09-15 GNU Linux Programmer's Manual