# remainder(3) — Linux manual page

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

## NAME         top

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

## SYNOPSIS         top

#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():
_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         top

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         top

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         top

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         top

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         top

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         top

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         top

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