# remainder - Man Page

floating-point remainder function

## Library

Math library (libm, -lm)

## Synopsis

```#include <math.h>

double remainder(double x, double y);
float remainderf(float x, float y);
long double remainderl(long double x, long double y);

/* Obsolete synonyms */
[[deprecated]] double drem(double x, double y);
[[deprecated]] float dremf(float x, float y);
[[deprecated]] long double dreml(long double x, long double y);```

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

remainder():

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

remainderf(), remainderl():

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

drem(), dremf(), dreml():

```    /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE```

## Description

These functions compute the remainder of dividing x by y. The return value is x-n*y, where n is the value x / y, rounded to the nearest integer. If the absolute value of x-n*y is 0.5, n is chosen to be even.

These functions are unaffected by the current rounding mode (see fenv(3)).

The drem() function does precisely the same thing.

## Return Value

On success, these functions return the floating-point remainder, x-n*y. If the return value is 0, it has the sign of x.

If x or y is a NaN, a NaN is returned.

If x is an infinity, and y is not a NaN, a domain error occurs, and a NaN is returned.

If y is zero, and x is not a NaN, a domain error occurs, and a NaN 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:

Domain error: x is an infinity and y is not a NaN

errno is set to EDOM (but see Bugs). An invalid floating-point exception (FE_INVALID) is raised.

These functions do not set errno for this case.

Domain error: y is zero

errno is set to EDOM. An invalid floating-point exception (FE_INVALID) is raised.

## Attributes

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

InterfaceAttributeValue
drem(), dremf(), dreml(), remainder(), remainderf(), remainderl()Thread safetyMT-Safe

## Standards

remainder()
remainderf()
remainderl()

C11, POSIX.1-2008.

drem()
dremf()
dreml()

None.

## History

remainder()
remainderf()
remainderl()

C99, POSIX.1-2001.

drem()

4.3BSD.

dremf()
dreml()

Tru64, glibc2.

## Bugs

Before glibc 2.15, the call

`remainder(nan(""), 0);`

returned a NaN, as expected, but wrongly caused a domain error. Since glibc 2.15, a silent NaN (i.e., no domain error) is returned.

Before glibc 2.15, errno was not set to EDOM for the domain error that occurs when x is an infinity and y is not a NaN.

## Examples

The call "remainder(29.0, 3.0)" returns -1.