add Readme

Author: oscardssmith

README.md

@@ -1 +1,10 @@
-# IntegerMathUtils.jl
+# IntegerMathUtils.jl
+
+This library adds several functions useful for doing math on integers. Most of these are just gmp wrappers that may have more specialized versions for smaller integer types.
+
+**Functions**
+
+* `iroot(x::Integer, n::integer)` the integer nth root of `x`. Specifically, this is the largest integer `a` such that `a^n <= x`. Note that `n` must fit into an `Int64` (for GMP compatability).
+* `ispower(x::Integer)` return if there are integer `base` and `exponent>1` values such that `base^exponent = x`.
+* `find_exponent(x::Integer)` returns the largest possible integer `exponent` such that `base^exponent = x` for some `base`. Returns `1` for `x ∈ [0,1]`.
+* `is_probably_prime(x::Integer; reps=25)` returns if `x` is prime. Will be incorrect less than `4^-reps` of the time.