remainderf (3)
Leading comments
Copyright 1993 David Metcalfe (david@prism.demon.co.uk) and Copyright 2008, Linux Foundation, written by Michael Kerrisk <mtk.manpages@gmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire ...
NAME
drem, dremf, dreml, remainder, remainderf, remainderl  floatingpoint remainder functionSYNOPSIS
#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():

_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 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.
RETURN VALUE
On success, these functions return the floatingpoint 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.
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 floatingpoint exception (FE_INVALID) is raised.
 These functions do not set errno for this case.
 Domain error: y is zeroerrno
 is set to EDOM. An invalid floatingpoint 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(),
remainder(), remainderf(), remainderl()  Thread safety  MTSafe 
CONFORMING TO
The functions remainder(), remainderf(), and remainderl() are specified in C99, POSIX.12001, and POSIX.12008.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 callremainder(nan(""), 0);
returns a NaN, as expected, but wrongly causes a domain error; it should yield a silent NaN.