SIMPLE SOLUTIONS

# REMAINDER(3) - man page online | library functions

Floating-point remainder function.

Chapter
2015-04-19
```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.