drem (3)  Linux Manuals
drem: floatingpoint remainder function
NAME
drem, dremf, dreml, remainder, remainderf, remainderl  floatingpoint 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);Link with lm.
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
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
 errno is set to EDOM (but see BUGS). 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
Before glibc 2.15, the call
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.COLOPHON
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