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    // Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    //! A Big integer (signed version: `BigInt`, unsigned version: `BigUint`).
    //!
    //! A `BigUint` is represented as a vector of `BigDigit`s.
    //! A `BigInt` is a combination of `BigUint` and `Sign`.
    //!
    //! Common numerical operations are overloaded, so we can treat them
    //! the same way we treat other numbers.
    //!
    //! ## Example
    //!
    //! ```rust
    //! extern crate num_bigint;
    //! extern crate num_traits;
    //!
    //! # fn main() {
    //! use num_bigint::BigUint;
    //! use num_traits::{Zero, One};
    //! use std::mem::replace;
    //!
    //! // Calculate large fibonacci numbers.
    //! fn fib(n: usize) -> BigUint {
    //!     let mut f0: BigUint = Zero::zero();
    //!     let mut f1: BigUint = One::one();
    //!     for _ in 0..n {
    //!         let f2 = f0 + &f1;
    //!         // This is a low cost way of swapping f0 with f1 and f1 with f2.
    //!         f0 = replace(&mut f1, f2);
    //!     }
    //!     f0
    //! }
    //!
    //! // This is a very large number.
    //! println!("fib(1000) = {}", fib(1000));
    //! # }
    //! ```
    //!
    //! It's easy to generate large random numbers:
    //!
    //! ```rust
    //! extern crate rand;
    //! extern crate num_bigint as bigint;
    //!
    //! # #[cfg(feature = "rand")]
    //! # fn main() {
    //! use bigint::{ToBigInt, RandBigInt};
    //!
    //! let mut rng = rand::thread_rng();
    //! let a = rng.gen_bigint(1000);
    //!
    //! let low = -10000.to_bigint().unwrap();
    //! let high = 10000.to_bigint().unwrap();
    //! let b = rng.gen_bigint_range(&low, &high);
    //!
    //! // Probably an even larger number.
    //! println!("{}", a * b);
    //! # }
    //!
    //! # #[cfg(not(feature = "rand"))]
    //! # fn main() {
    //! # }
    //! ```
    #![doc(html_logo_url = "https://rust-num.github.io/num/rust-logo-128x128-blk-v2.png",
           html_favicon_url = "https://rust-num.github.io/num/favicon.ico",
           html_root_url = "https://rust-num.github.io/num/",
           html_playground_url = "http://play.integer32.com/")]

    #[cfg(any(feature = "rand", test))]
    extern crate rand;
    #[cfg(feature = "rustc-serialize")]
    extern crate rustc_serialize;
    #[cfg(feature = "serde")]
    extern crate serde;

    extern crate num_integer as integer;
    extern crate num_traits as traits;

    use std::error::Error;
    use std::num::ParseIntError;
    use std::fmt;

    #[cfg(target_pointer_width = "32")]
    type UsizePromotion = u32;
    #[cfg(target_pointer_width = "64")]
    type UsizePromotion = u64;

    #[cfg(target_pointer_width = "32")]
    type IsizePromotion = i32;
    #[cfg(target_pointer_width = "64")]
    type IsizePromotion = i64;

    #[derive(Debug, PartialEq)]
    pub enum ParseBigIntError {
        ParseInt(ParseIntError),
        Other,
    }

    impl fmt::Display for ParseBigIntError {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            match self {
                &ParseBigIntError::ParseInt(ref e) => e.fmt(f),
                &ParseBigIntError::Other => "failed to parse provided string".fmt(f),
            }
        }
    }

    impl Error for ParseBigIntError {
        fn description(&self) -> &str {
            "failed to parse bigint/biguint"
        }
    }

    impl From<ParseIntError> for ParseBigIntError {
        fn from(err: ParseIntError) -> ParseBigIntError {
            ParseBigIntError::ParseInt(err)
        }
    }

    #[cfg(test)]
    use std::hash;

    #[cfg(test)]
    fn hash<T: hash::Hash>(x: &T) -> u64 {
        use std::hash::{BuildHasher, Hasher};
        use std::collections::hash_map::RandomState;
        let mut hasher = <RandomState as BuildHasher>::Hasher::new();
        x.hash(&mut hasher);
        hasher.finish()
    }

    #[macro_use]
    mod macros;

    mod biguint;
    mod bigint;

    pub use biguint::BigUint;
    pub use biguint::ToBigUint;
    pub use biguint::big_digit;
    pub use biguint::big_digit::{BigDigit, DoubleBigDigit, ZERO_BIG_DIGIT};

    pub use bigint::Sign;
    pub use bigint::BigInt;
    pub use bigint::ToBigInt;
    pub use bigint::RandBigInt;

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