remainder(3) Library Functions Manual remainder(3)

# NAME

drem, dremf, dreml, remainder, remainderf, remainderl - 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:

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.
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).

 Interface Attribute Value drem (), dremf (), dreml (), remainder (), remainderf (), remainderl () Thread safety MT-Safe

# STANDARDS

C11, POSIX.1-2008.
None.

# HISTORY

C99, POSIX.1-2001.
4.3BSD.
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.