float

convert a float value to i64 dropping any fraction.
the value must be in the range of i64

ceiling: the smallest integer greater or equal to this

floor: the greatest integer lower or equal to this

preconditions for basic operations: true if the operation's result is
representable for the given values. For IEEE_754, all operations are
defined for all values.

round floating point number
ties to away (0.5 => 1; -0.5 => -1; etc.)

NYI this could be made faster, see here:
https://cs.opensource.google/go/go/+/refs/tags/go1.18.1:src/math/floor.go;l=79