MLtonIntInf
===========

[source,sml]
----
signature MLTON_INT_INF =
   sig
      type t = IntInf.int

      val areSmall: t * t -> bool
      val gcd: t * t -> t
      val isSmall: t -> bool

      structure BigWord : WORD
      structure SmallInt : INTEGER
      datatype rep =
         Big of BigWord.word vector
       | Small of SmallInt.int
      val rep: t -> rep
      val fromRep : rep -> t option
   end
----

MLton represents an arbitrary precision integer either as an unboxed
word with the bottom bit set to 1 and the top bits representing a
small signed integer, or as a pointer to a vector of words, where the
first word indicates the sign and the rest are the limbs of a
<:GMP:> big integer.

* `type t`
+
the same as type `IntInf.int`.

* `areSmall (a, b)`
+
returns true iff both `a` and `b` are small.

* `gcd (a, b)`
+
uses <:GMP:GMP's> fast gcd implementation.

* `isSmall a`
+
returns true iff `a` is small.

* `BigWord : WORD`
+
representation of a big `IntInf.int` as a vector of words; on 32-bit
platforms, `BigWord` is likely to be equivalent to `Word32`, and on
64-bit platforms, `BigWord` is likely to be equivalent to `Word64`.

* `SmallInt : INTEGER`
+
representation of a small `IntInf.int` as a signed integer; on 32-bit
platforms, `SmallInt` is likely to be equivalent to `Int32`, and on
64-bit platforms, `SmallInt` is likely to be equivalent to `Int64`.

* `datatype rep`
+
the underlying representation of an `IntInf.int`.

* `rep i`
+
returns the underlying representation of `i`.

* `fromRep r`
+
converts from the underlying representation back to an `IntInf.int`.  
If `fromRep r` is given anything besides the valid result of `rep i`
for some `i`, this function call will return `NONE`.
