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:

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
 | Thread safety | MT-Safe

STANDARDS

remainder()
remainderf()
remainderl()
    C11, POSIX.1-2008.

drem()
dremf()
dreml()
    None.

HISTORY

remainder()
remainderf()
remainderl()
    C99, POSIX.1-2001.

drem()
    4.3BSD.

dremf()
dreml()
    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.

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