The
fmod() function computes 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.

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.

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A description of the project,
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can be found at
http://www.kernel.org/doc/man-pages/.