The functions in this section compute the remainder on division of two
floating-point numbers. Each is a little different; pick the one that
suits your problem.

— Function: long double fmodl (long double numerator, long double denominator)

These functions compute the remainder from the division of
numerator by denominator. Specifically, the return value is
numerator - n * denominator, where n
is the quotient of numerator divided by denominator, rounded
towards zero to an integer. Thus, fmod (6.5, 2.3) returns
1.9, which is 6.5 minus 4.6.

The result has the same sign as the numerator and has magnitude
less than the magnitude of the denominator.

If denominator is zero, fmod signals a domain error.

— Function: long double dreml (long double numerator, long double denominator)

These functions are like fmod except that they rounds the
internal quotient n to the nearest integer instead of towards zero
to an integer. For example, drem (6.5, 2.3) returns -0.4,
which is 6.5 minus 6.9.

The absolute value of the result is less than or equal to half the
absolute value of the denominator. The difference between
fmod (numerator, denominator) and drem
(numerator, denominator) is always either
denominator, minus denominator, or zero.

If denominator is zero, drem signals a domain error.