Merge pull request #305 from jialunzhang-psu/bigint

Bigint

bigint/README.md

@@ -0,0 +1,17 @@
+# Big Integer
+
+## Description
+
+An immutable arbitrary precision integer type. Currently it supports the following.
+- Basic arithmetic operations, including addition, subtraction, multiplication, division, and modulo.
+- Conversion from `Int` and `Int64` to `BigInt`.
+- Conversion between `BigInt` and `String` (in decimal format).
+- Comparison between `BigInt`.
+
+## TODO
+
+- `op_mod` is now implemented by `op_div`. Implement it separately for performance.
+- Add +-*/ operators between`BigInt` and `Int`.
+- From/To hex string, etc.
+- Optimize the implementation of multiplication and division by doing a case analysis on the length of the numbers. For example, currently `op_mul` opts in Karatsuba algorithm when one of the operand's length goes beyond `karatsuba_threshold`. A more elaborated example can be found [here](https://github.com/tbuktu/bigint).
+- Other math function, like power, sqrt, log, etc.