
  -spec trunc(Number) -> integer() when Number :: number().

  Truncates the decimals of Number, for example:

    > trunc(5.7).
    5

    > trunc(-5.7).
    -5

    > trunc(5).
    5

    > trunc(36028797018963969.0).
    36028797018963968

  In the last example, trunc(36028797018963969.0) evaluates to 
  36028797018963968. The reason for this is that the number 
  36028797018963969.0 cannot be represented exactly as a float
  value. Instead, the float literal is represented as 
  36028797018963968.0, which is the closest number that can be
  represented exactly as a float value. See Representation of
  Floating Point Numbers for additional information.

  Allowed in guard tests.
