# drem

```REMAINDER(3)               Linux Programmer's Manual              REMAINDER(3)

NAME
drem,  dremf, dreml, remainder, remainderf, remainderl - floating-point
remainder function

SYNOPSIS
#include <math.h>

/* The C99 versions */
double remainder(double x, double y);
float remainderf(float x, float y);
long double remainderl(long double x, long double y);

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

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

remainder():
_SVID_SOURCE || _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
remainderf(), remainderl():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
drem(), dremf(), dreml():
_SVID_SOURCE || _BSD_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
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).

+---------------------------+---------------+---------+
|Interface                  | Attribute     | Value   |
+---------------------------+---------------+---------+
|drem(), dremf(), dreml(),  | Thread safety | MT-Safe |
|remainder(), remainderf(), |               |         |
|remainderl()               |               |         |
+---------------------------+---------------+---------+
CONFORMING TO
The functions remainder(), remainderf(), and remainderl() are specified
in C99, POSIX.1-2001, and POSIX.1-2008.

The function drem() is from 4.3BSD.  The float and long double variants
dremf()  and  dreml()  exist on some systems, such as Tru64 and glibc2.
Avoid the use of these functions in favor of remainder() etc.

BUGS
The call

remainder(nan(""), 0);

returns a NaN, as expected, but  wrongly  causes  a  domain  error;  it
should yield a silent NaN.

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