# Linux 2.6 - man page for remainder (linux section 3)

```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);

Link with -lm.

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 versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
remainderf(), remainderl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
drem(), dremf(), dreml():
/* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 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).

+---------------------------+---------------+---------+
|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
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.

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

SEE ALSO
div(3), fmod(3), remquo(3)

2017-09-15							      REMAINDER(3)```