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    // Copyright 2018 Developers of the Rand project.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    //! Entropy generator, or wrapper around external generators

    #![allow(deprecated)]   // whole module is deprecated

    use rand_core::{RngCore, CryptoRng, Error};
    #[allow(unused)]
    use crate::rngs::OsRng;

    /// An interface returning random data from external source(s), provided
    /// specifically for securely seeding algorithmic generators (PRNGs).
    ///
    /// This is deprecated. It is suggested you use [`rngs::OsRng`] instead.
    ///
    /// [`rngs::OsRng`]: crate::rngs::OsRng
    #[derive(Debug)]
    #[deprecated(since="0.7.0", note="use rngs::OsRng instead")]
    pub struct EntropyRng {
        source: OsRng,
    }

    impl EntropyRng {
        /// Create a new `EntropyRng`.
        ///
        /// This method will do no system calls or other initialization routines,
        /// those are done on first use. This is done to make `new` infallible,
        /// and `try_fill_bytes` the only place to report errors.
        pub fn new() -> Self {
            EntropyRng { source: OsRng }
        }
    }

    impl Default for EntropyRng {
        fn default() -> Self {
            EntropyRng::new()
        }
    }

    impl RngCore for EntropyRng {
        fn next_u32(&mut self) -> u32 {
            self.source.next_u32()
        }

        fn next_u64(&mut self) -> u64 {
            self.source.next_u64()
        }

        fn fill_bytes(&mut self, dest: &mut [u8]) {
            self.source.fill_bytes(dest)
        }

        fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
            self.source.try_fill_bytes(dest)
        }
    }

    impl CryptoRng for EntropyRng {}

    #[cfg(test)]
    mod test {
        use super::*;

        #[test]
        fn test_entropy() {
            let mut rng = EntropyRng::new();
            let n = (rng.next_u32() ^ rng.next_u32()).count_ones();
            assert!(n >= 2);    // p(failure) approx 1e-7
        }
    }

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