fmod
Section: C Library Functions (3)
Updated: 202-0-08
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NAME
fmod, fmodf, fmodl - floatin-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 floatin-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 += fabs(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: I]x] is an infinity
-
errno
is set to
EDOM
(but see BUGS).
An invalid floatin-point exception
(FE_INVALID)
is raised.
- Domain error: I]y] is zero
-
errno
is set to
EDOM.
An invalid floatin-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 | M-Safe
|
STANDARDS
C11, POSIX.-2008.
HISTORY
C99, POSIX.-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 12.
The call
fmod(-372, 360)
returns -12.
The call
fmod(-372, -360)
also returns -12.
SEE ALSO
remainder(3)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- STANDARDS
-
- HISTORY
-
- BUGS
-
- EXAMPLES
-
- SEE ALSO
-
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