//! The `mulX_POLYVAL()` function.

use crate::Block;

/// The `mulX_POLYVAL()` function as defined in [RFC 8452 Appendix A][1].

///

/// Performs a doubling (a.k.a. "multiply by x") over GF(2^128).

/// This is useful for implementing GHASH in terms of POLYVAL.

///

/// [1]: https://tools.ietf.org/html/rfc8452#appendix-A

pub fn mulx(block: &Block) -> Block {

    let mut v = u128::from_le_bytes((*block).into());

    let v_hi = v >> 127;

    v <<= 1;

    v ^= v_hi ^ (v_hi << 127) ^ (v_hi << 126) ^ (v_hi << 121);

    v.to_le_bytes().into()

}

polyval::mulx::mulx

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pub fn mulx(block: &Block) -> Block {

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    let mut v = u128::from_le_bytes((*block).into());

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    let v_hi = v >> 127;

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    v <<= 1;

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    v ^= v_hi ^ (v_hi << 127) ^ (v_hi << 126) ^ (v_hi << 121);

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    v.to_le_bytes().into()

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}

polyval::mulx::mulx

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pub fn mulx(block: &Block) -> Block {

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    let mut v = u128::from_le_bytes((*block).into());

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    let v_hi = v >> 127;

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    v <<= 1;

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    v ^= v_hi ^ (v_hi << 127) ^ (v_hi << 126) ^ (v_hi << 121);

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    v.to_le_bytes().into()

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}

#[cfg(test)]

mod tests {

    use super::{mulx, Block};

    use hex_literal::hex;

    /// Test vector given in RFC 8452 Appendix A.

    ///

    /// NOTE: the vector in the RFC actually contains a typo which has been

    /// reported (and accepted) as RFC errata, so we use the vector from the

    /// errata instead:

    ///

    /// <https://www.rfc-editor.org/errata_search.php?rfc=8452>

    #[test]

    fn rfc8452_vector() {

        let input = Block::from(hex!("9c98c04df9387ded828175a92ba652d8"));

        let expected_output = Block::from(hex!("3931819bf271fada0503eb52574ca572"));

        let actual_output = mulx(&input);

        assert_eq!(expected_output, actual_output);

    }

    /// Test against the `MULX_TEST_VECTORS` given below, which cover the full

    /// size of a POLYVAL field element.

    #[test]

    fn mulx_vectors() {

        // One

        let mut r = Block::from(hex!("01000000000000000000000000000000"));

        for vector in MULX_TEST_VECTORS {

            r = mulx(&r);

            assert_eq!(&r, Block::from_slice(vector));

        }

    }

    /// `mulX_POLYVAL()` test vectors.

    ///

    /// These were generated by this crate when in a known-correct state,

    /// verified by a GHASH implementation based on a POLYVAL core successfully

    /// passing the NIST test vectors.

    const MULX_TEST_VECTORS: &[[u8; 16]] = &[

        hex!("02000000000000000000000000000000"),

        hex!("04000000000000000000000000000000"),

        hex!("08000000000000000000000000000000"),

        hex!("10000000000000000000000000000000"),

        hex!("20000000000000000000000000000000"),

        hex!("40000000000000000000000000000000"),

        hex!("80000000000000000000000000000000"),

        hex!("00010000000000000000000000000000"),

        hex!("00020000000000000000000000000000"),

        hex!("00040000000000000000000000000000"),

        hex!("00080000000000000000000000000000"),

        hex!("00100000000000000000000000000000"),

        hex!("00200000000000000000000000000000"),

        hex!("00400000000000000000000000000000"),

        hex!("00800000000000000000000000000000"),

        hex!("00000100000000000000000000000000"),

        hex!("00000200000000000000000000000000"),

        hex!("00000400000000000000000000000000"),

        hex!("00000800000000000000000000000000"),

        hex!("00001000000000000000000000000000"),

        hex!("00002000000000000000000000000000"),

        hex!("00004000000000000000000000000000"),

        hex!("00008000000000000000000000000000"),

        hex!("00000001000000000000000000000000"),

        hex!("00000002000000000000000000000000"),

        hex!("00000004000000000000000000000000"),

        hex!("00000008000000000000000000000000"),

        hex!("00000010000000000000000000000000"),

        hex!("00000020000000000000000000000000"),

        hex!("00000040000000000000000000000000"),

        hex!("00000080000000000000000000000000"),

        hex!("00000000010000000000000000000000"),

        hex!("00000000020000000000000000000000"),

        hex!("00000000040000000000000000000000"),

        hex!("00000000080000000000000000000000"),

        hex!("00000000100000000000000000000000"),

        hex!("00000000200000000000000000000000"),

        hex!("00000000400000000000000000000000"),

        hex!("00000000800000000000000000000000"),

        hex!("00000000000100000000000000000000"),

        hex!("00000000000200000000000000000000"),

        hex!("00000000000400000000000000000000"),

        hex!("00000000000800000000000000000000"),

        hex!("00000000001000000000000000000000"),

        hex!("00000000002000000000000000000000"),

        hex!("00000000004000000000000000000000"),

        hex!("00000000008000000000000000000000"),

        hex!("00000000000001000000000000000000"),

        hex!("00000000000002000000000000000000"),

        hex!("00000000000004000000000000000000"),

        hex!("00000000000008000000000000000000"),

        hex!("00000000000010000000000000000000"),

        hex!("00000000000020000000000000000000"),

        hex!("00000000000040000000000000000000"),

        hex!("00000000000080000000000000000000"),

        hex!("00000000000000010000000000000000"),

        hex!("00000000000000020000000000000000"),

        hex!("00000000000000040000000000000000"),

        hex!("00000000000000080000000000000000"),

        hex!("00000000000000100000000000000000"),

        hex!("00000000000000200000000000000000"),

        hex!("00000000000000400000000000000000"),

        hex!("00000000000000800000000000000000"),

        hex!("00000000000000000100000000000000"),

        hex!("00000000000000000200000000000000"),

        hex!("00000000000000000400000000000000"),

        hex!("00000000000000000800000000000000"),

        hex!("00000000000000001000000000000000"),

        hex!("00000000000000002000000000000000"),

        hex!("00000000000000004000000000000000"),

        hex!("00000000000000008000000000000000"),

        hex!("00000000000000000001000000000000"),

        hex!("00000000000000000002000000000000"),

        hex!("00000000000000000004000000000000"),

        hex!("00000000000000000008000000000000"),

        hex!("00000000000000000010000000000000"),

        hex!("00000000000000000020000000000000"),

        hex!("00000000000000000040000000000000"),

        hex!("00000000000000000080000000000000"),

        hex!("00000000000000000000010000000000"),

        hex!("00000000000000000000020000000000"),

        hex!("00000000000000000000040000000000"),

        hex!("00000000000000000000080000000000"),

        hex!("00000000000000000000100000000000"),

        hex!("00000000000000000000200000000000"),

        hex!("00000000000000000000400000000000"),

        hex!("00000000000000000000800000000000"),

        hex!("00000000000000000000000100000000"),

        hex!("00000000000000000000000200000000"),

        hex!("00000000000000000000000400000000"),

        hex!("00000000000000000000000800000000"),

        hex!("00000000000000000000001000000000"),

        hex!("00000000000000000000002000000000"),

        hex!("00000000000000000000004000000000"),

        hex!("00000000000000000000008000000000"),

        hex!("00000000000000000000000001000000"),

        hex!("00000000000000000000000002000000"),

        hex!("00000000000000000000000004000000"),

        hex!("00000000000000000000000008000000"),

        hex!("00000000000000000000000010000000"),

        hex!("00000000000000000000000020000000"),

        hex!("00000000000000000000000040000000"),

        hex!("00000000000000000000000080000000"),

        hex!("00000000000000000000000000010000"),

        hex!("00000000000000000000000000020000"),

        hex!("00000000000000000000000000040000"),

        hex!("00000000000000000000000000080000"),

        hex!("00000000000000000000000000100000"),

        hex!("00000000000000000000000000200000"),

        hex!("00000000000000000000000000400000"),

        hex!("00000000000000000000000000800000"),

        hex!("00000000000000000000000000000100"),

        hex!("00000000000000000000000000000200"),

        hex!("00000000000000000000000000000400"),

        hex!("00000000000000000000000000000800"),

        hex!("00000000000000000000000000001000"),

        hex!("00000000000000000000000000002000"),

        hex!("00000000000000000000000000004000"),

        hex!("00000000000000000000000000008000"),

        hex!("00000000000000000000000000000001"),

        hex!("00000000000000000000000000000002"),

        hex!("00000000000000000000000000000004"),

        hex!("00000000000000000000000000000008"),

        hex!("00000000000000000000000000000010"),

        hex!("00000000000000000000000000000020"),

        hex!("00000000000000000000000000000040"),

        hex!("00000000000000000000000000000080"),

        hex!("010000000000000000000000000000c2"),

    ];

}