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fdim

Section: C Library Functions (3)
Updated: 2026-02-08
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NAME

fdim, fdimf, fdiml - positive difference

LIBRARY

Math library (libm,~-lm)

SYNOPSIS

#include <math.h>
double fdim(double x, double y);
float fdimf(float x, float y);
long double fdiml(long double x, long double y);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)): fdimf(), fdiml():

    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

DESCRIPTION

These functions return the positive difference, max(x-y,0), between their arguments.

RETURN VALUE

On success, these functions return the positive difference. If x or y is a NaN, a NaN is returned. If the result overflows, a range error occurs, and the functions return HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively.

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.

ATTRIBUTES

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

Interface	Attribute	Value
fdim(), fdimf(), fdiml()	Thread safety	MT-Safe

STANDARDS

C11, POSIX.1-2008.

HISTORY

glibc 2.1. C99, POSIX.1-2001.

BUGS

Before glibc 2.24 on certain architectures (e.g., x86, but not x86_64) these functions did not set errno.