This is a special version of the regular
It works by directly calling the low-level internal GHC
primitives, and thus is as fast as you'd expect for such
a trivial operation.
floor function does something crazy like
Double to a numerator/denominator
pair and then computing the integer part of the quotient as
Integer, then truncating that to a
obviously, is ludicrously slow.)
Hopefully one day the need for this low-level hackery will disappear.