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    // Copyright 2015-2017 Parity Technologies (UK) Ltd.
    // This file is part of Parity.

    // Parity is free software: you can redistribute it and/or modify
    // it under the terms of the GNU General Public License as published by
    // the Free Software Foundation, either version 3 of the License, or
    // (at your option) any later version.

    // Parity is distributed in the hope that it will be useful,
    // but WITHOUT ANY WARRANTY; without even the implied warranty of
    // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    // GNU General Public License for more details.

    //! Canonical hash trie definitions and helper functions.

    /// The size of each CHT.
    pub const SIZE: u64 = 2048;

    /// Convert a block number to a CHT number.
    /// Returns `None` for `block_num` == 0, `Some` otherwise.
    pub fn block_to_cht_number(block_num: u64) -> Option<u64> {
    	match block_num {
    		0 => None,
    		n => Some((n - 1) / SIZE),
    	}
    }

    /// Get the starting block of a given CHT.
    /// CHT 0 includes block 1...SIZE,
    /// CHT 1 includes block SIZE + 1 ... 2*SIZE
    /// More generally: CHT N includes block (1 + N*SIZE)...((N+1)*SIZE).
    /// This is because the genesis hash is assumed to be known
    /// and including it would be redundant.
    pub fn start_number(cht_num: u64) -> u64 {
    	(cht_num * SIZE) + 1
    }

    #[cfg(test)]
    mod tests {
    	#[test]
    	fn block_to_cht_number() {
    		assert!(::cht::block_to_cht_number(0).is_none());
    		assert_eq!(::cht::block_to_cht_number(1).unwrap(), 0);
    		assert_eq!(::cht::block_to_cht_number(::cht::SIZE + 1).unwrap(), 1);
    		assert_eq!(::cht::block_to_cht_number(::cht::SIZE).unwrap(), 0);
    	}

    	#[test]
    	fn start_number() {
    		assert_eq!(::cht::start_number(0), 1);
    		assert_eq!(::cht::start_number(1), ::cht::SIZE + 1);
    		assert_eq!(::cht::start_number(2), ::cht::SIZE * 2 + 1);
    	}
    }

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