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


#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);
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 500 || /* Since glibc 2.19:
*/ _DEFAULT_SOURCE || /* Glibc <= 2.19:
remainderf(), remainderl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19:
*/ _DEFAULT_SOURCE || /* Glibc <= 2.19:
drem(), dremf(), dreml():
/* Since glibc 2.19:
*/ _DEFAULT_SOURCE || /* Glibc <= 2.19:
[Note] Note

Link with −lm.


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


On success, these functions return the floating-point remainder, xn*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.


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.


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


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.


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.


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


div(3), fmod(3), remquo(3)


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Modified 1993-07-24 by Rik Faith (
Modified 2002-08-10 Walter Harms
Modified 2003-11-18, 2004-10-05 aeb