fmod(3) Library Functions Manual fmod(3)
NAME
fmod, fmodf, fmodl - floating-point remainder function
LIBRARY
Math library (libm, -lm)
SYNOPSIS
#include <math.h>
double fmod(double x, double y);
float fmodf(float x, float y);
long double fmodl(long double x, long double y);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
fmodf(), fmodl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
These functions compute the floating-point remainder of dividing x by y.
The return value is x - n * y, where n is the quotient of x / y, rounded
toward zero to an integer.
To obtain the modulus, more specifically, the Least Positive Residue,
you will need to adjust the result from fmod like so:
z = fmod(x, y);
if (z < 0)
z += y;
An alternate way to express this is with fmod(fmod(x, y) + y, y), but
the second fmod() usually costs way more than the one branch.
RETURN VALUE
On success, these functions return the value x - n*y, for some integer
n, such that the returned value has the same sign as x and a magnitude
less than the magnitude of y.
If x or y is a NaN, a NaN is returned.
If x is an infinity, a domain error occurs, and a NaN is returned.
If y is zero, a domain error occurs, and a NaN is returned.
If x is +0 (-0), and y is not zero, +0 (-0) 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
errno is set to EDOM (but see BUGS). An invalid floating-point
exception (FE_INVALID) is raised.
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 │
├────────────────────────────────────────────┼───────────────┼─────────┤
│ fmod(), fmodf(), fmodl() │ Thread safety │ MT-Safe │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
C11, POSIX.1-2008.
HISTORY
C99, POSIX.1-2001.
The variant returning double also conforms to SVr4, 4.3BSD, C89.
BUGS
Before glibc 2.10, the glibc implementation did not set errno to EDOM
when a domain error occurred for an infinite x.
EXAMPLES
The call fmod(372, 360) returns 348.
The call fmod(-372, 360) returns -12.
The call fmod(-372, -360) also returns -12.
SEE ALSO
remainder(3)
Linux man-pages 6.9.1 2024-05-02 fmod(3)
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