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    // Copyright 2015-2017 Brian Smith.
    //
    // Permission to use, copy, modify, and/or distribute this software for any
    // purpose with or without fee is hereby granted, provided that the above
    // copyright notice and this permission notice appear in all copies.
    //
    // THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
    // WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
    // MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
    // SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    // WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
    // OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
    // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

    //! SHA-2 and the legacy SHA-1 digest algorithm.
    //!
    //! If all the data is available in a single contiguous slice then the `digest`
    //! function should be used. Otherwise, the digest can be calculated in
    //! multiple steps using `Context`.

    // Note on why are we doing things the hard way: It would be easy to implement
    // this using the C `EVP_MD`/`EVP_MD_CTX` interface. However, if we were to do
    // things that way, we'd have a hard dependency on `malloc` and other overhead.
    // The goal for this implementation is to drive the overhead as close to zero
    // as possible.

    use {c, init, polyfill};
    use core;

    // XXX: Replace with `const fn` when `const fn` is stable:
    // https://github.com/rust-lang/rust/issues/24111
    #[cfg(target_endian = "little")]
    macro_rules! u32x2 {
        ( $first:expr, $second:expr ) =>
        ( ((($second as u64) << 32) | ($first as u64)) )
    }

    mod sha1;

    /// A context for multi-step (Init-Update-Finish) digest calculations.
    ///
    /// C analog: `EVP_MD_CTX`.
    ///
    /// # Examples
    ///
    /// ```
    /// use ring::digest;
    ///
    /// let one_shot = digest::digest(&digest::SHA384, b"hello, world");
    ///
    /// let mut ctx = digest::Context::new(&digest::SHA384);
    /// ctx.update(b"hello");
    /// ctx.update(b", ");
    /// ctx.update(b"world");
    /// let multi_part = ctx.finish();
    ///
    /// assert_eq!(&one_shot.as_ref(), &multi_part.as_ref());
    /// ```
    pub struct Context {
        state: State,

        // Note that SHA-512 has a 128-bit input bit counter, but this
        // implementation only supports up to 2^64-1 input bits for all algorithms,
        // so a 64-bit counter is more than sufficient.
        completed_data_blocks: u64,

        // TODO: More explicitly force 64-bit alignment for |pending|.
        pending: [u8; MAX_BLOCK_LEN],
        num_pending: usize,

        /// The context's algorithm.
        pub algorithm: &'static Algorithm,
    }

    impl Context {
        /// Constructs a new context.
        ///
        /// C analogs: `EVP_DigestInit`, `EVP_DigestInit_ex`
        pub fn new(algorithm: &'static Algorithm) -> Context {
            init::init_once();

            Context {
                algorithm: algorithm,
                state: algorithm.initial_state,
                completed_data_blocks: 0,
                pending: [0u8; MAX_BLOCK_LEN],
                num_pending: 0,
            }
        }

        /// Updates the digest with all the data in `data`. `update` may be called
        /// zero or more times until `finish` is called. It must not be called
        /// after `finish` has been called.
        ///
        /// C analog: `EVP_DigestUpdate`
        pub fn update(&mut self, data: &[u8]) {
            if data.len() < self.algorithm.block_len - self.num_pending {
                self.pending[self.num_pending..(self.num_pending + data.len())]
                    .copy_from_slice(data);
                self.num_pending += data.len();
                return;
            }

            let mut remaining = data;
            if self.num_pending > 0 {
                let to_copy = self.algorithm.block_len - self.num_pending;
                self.pending[self.num_pending..self.algorithm.block_len]
                    .copy_from_slice(&data[..to_copy]);

                unsafe {
                    (self.algorithm.block_data_order)(&mut self.state,
                                                      self.pending.as_ptr(), 1);
                }
                self.completed_data_blocks =
                    self.completed_data_blocks.checked_add(1).unwrap();

                remaining = &remaining[to_copy..];
                self.num_pending = 0;
            }

            let num_blocks = remaining.len() / self.algorithm.block_len;
            let num_to_save_for_later = remaining.len() % self.algorithm.block_len;
            if num_blocks > 0 {
                unsafe {
                    (self.algorithm.block_data_order)(&mut self.state,
                                                      remaining.as_ptr(),
                                                      num_blocks);
                }
                self.completed_data_blocks =
                    self.completed_data_blocks
                        .checked_add(polyfill::u64_from_usize(num_blocks))
                        .unwrap();
            }
            if num_to_save_for_later > 0 {
                self.pending[..num_to_save_for_later]
                    .copy_from_slice(&remaining[(remaining.len() -
                                                 num_to_save_for_later)..]);
                self.num_pending = num_to_save_for_later;
            }
        }

        /// Finalizes the digest calculation and returns the digest value. `finish`
        /// consumes the context so it cannot be (mis-)used after `finish` has been
        /// called.
        ///
        /// C analogs: `EVP_DigestFinal`, `EVP_DigestFinal_ex`
        pub fn finish(mut self) -> Digest {
            // We know |num_pending < self.algorithm.block_len|, because we would
            // have processed the block otherwise.

            let mut padding_pos = self.num_pending;
            self.pending[padding_pos] = 0x80;
            padding_pos += 1;

            if padding_pos > self.algorithm.block_len - self.algorithm.len_len {
                polyfill::slice::fill(
                    &mut self.pending[padding_pos..self.algorithm.block_len], 0);
                unsafe {
                    (self.algorithm.block_data_order)(&mut self.state,
                                                      self.pending.as_ptr(), 1);
                }
                // We don't increase |self.completed_data_blocks| because the
                // padding isn't data, and so it isn't included in the data length.
                padding_pos = 0;
            }

            polyfill::slice::fill(
                &mut self.pending[padding_pos..(self.algorithm.block_len - 8)], 0);

            // Output the length, in bits, in big endian order.
            let mut completed_data_bits: u64 = self.completed_data_blocks
                .checked_mul(polyfill::u64_from_usize(self.algorithm.block_len))
                .unwrap()
                .checked_add(polyfill::u64_from_usize(self.num_pending)).unwrap()
                .checked_mul(8).unwrap();

            for b in (&mut self.pending[(self.algorithm.block_len - 8)..
                                        self.algorithm.block_len]).into_iter().rev() {
                *b = completed_data_bits as u8;
                completed_data_bits /= 0x100;
            }
            unsafe {
                (self.algorithm.block_data_order)(&mut self.state,
                                                  self.pending.as_ptr(), 1);
            }

            Digest {
                algorithm: self.algorithm,
                value: (self.algorithm.format_output)(&self.state),
            }
        }

        /// The algorithm that this context is using.
        #[inline(always)]
        pub fn algorithm(&self) -> &'static Algorithm { self.algorithm }
    }

    // XXX: This should just be `#[derive(Clone)]` but that doesn't work because
    // `[u8; 128]` doesn't implement `Clone`.
    impl Clone for Context {
        fn clone(&self) -> Context {
            Context {
                state: self.state,
                pending: self.pending,
                completed_data_blocks: self.completed_data_blocks,
                num_pending: self.num_pending,
                algorithm: self.algorithm,
            }
        }
    }

    /// Returns the digest of `data` using the given digest algorithm.
    ///
    /// C analog: `EVP_Digest`
    ///
    /// # Examples:
    ///
    /// ```
    /// # #[cfg(feature = "use_heap")]
    /// # fn main() {
    /// use ring::{digest, test};
    ///
    /// let expected_hex =
    ///     "09ca7e4eaa6e8ae9c7d261167129184883644d07dfba7cbfbc4c8a2e08360d5b";
    /// let expected: Vec<u8> = test::from_hex(expected_hex).unwrap();
    /// let actual = digest::digest(&digest::SHA256, b"hello, world");
    ///
    /// assert_eq!(&expected, &actual.as_ref());
    /// # }
    ///
    /// # #[cfg(not(feature = "use_heap"))]
    /// # fn main() { }
    /// ```
    pub fn digest(algorithm: &'static Algorithm, data: &[u8]) -> Digest {
        let mut ctx = Context::new(algorithm);
        ctx.update(data);
        ctx.finish()
    }

    /// A calculated digest value.
    ///
    /// Use `as_ref` to get the value as a `&[u8]`.
    #[derive(Clone, Copy)]
    pub struct Digest {
        value: Output,
        algorithm: &'static Algorithm,
    }

    impl Digest {
        /// The algorithm that was used to calculate the digest value.
        #[inline(always)]
        pub fn algorithm(&self) -> &'static Algorithm { self.algorithm }
    }

    impl AsRef<[u8]> for Digest {
        #[inline(always)]
        fn as_ref(&self) -> &[u8] {
            &(polyfill::slice::u64_as_u8(&self.value))[..self.algorithm.output_len]
        }
    }

    impl core::fmt::Debug for Digest {
        fn fmt(&self, fmt: &mut core::fmt::Formatter) -> core::fmt::Result {
            write!(fmt, "{:?}:", self.algorithm)?;
            for byte in self.as_ref() {
                write!(fmt, "{:02x}", byte)?;
            }
            Ok(())
        }
    }

    /// A digest algorithm.
    ///
    /// C analog: `EVP_MD`
    pub struct Algorithm {
        /// C analog: `EVP_MD_size`
        pub output_len: usize,

        /// The size of the chaining value of the digest function, in bytes. For
        /// non-truncated algorithms (SHA-1, SHA-256, SHA-512), this is equal to
        /// `output_len`. For truncated algorithms (e.g. SHA-384, SHA-512/256),
        /// this is equal to the length before truncation. This is mostly helpful
        /// for determining the size of an HMAC key that is appropriate for the
        /// digest algorithm.
        pub chaining_len: usize,

        /// C analog: `EVP_MD_block_size`
        pub block_len: usize,

        /// The length of the length in the padding.
        len_len: usize,

        block_data_order: unsafe extern fn(state: &mut State, data: *const u8,
                                           num: c::size_t),
        format_output: fn(input: &State) -> Output,

        initial_state: State,
    }

    impl core::fmt::Debug for Algorithm {
        fn fmt(&self, fmt: &mut core::fmt::Formatter) -> core::fmt::Result {
            // This would have to change if/when we add other algorithms with the
            // same lengths.
            let (n, suffix) =
                if self.output_len == SHA512_256_OUTPUT_LEN &&
                   self.block_len == SHA512_BLOCK_LEN {
                (512, "_256")
            } else if self.output_len == 20 {
                (1, "")
            } else {
                (self.output_len * 8, "")
            };
            write!(fmt, "SHA{}{}", n, suffix)
        }
    }

    /// SHA-1 as specified in [FIPS 180-4]. Deprecated.
    ///
    /// [FIPS 180-4]: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
    pub static SHA1: Algorithm = Algorithm {
        output_len: sha1::OUTPUT_LEN,
        chaining_len: sha1::CHAINING_LEN,
        block_len: sha1::BLOCK_LEN,
        len_len: 64 / 8,
        block_data_order: sha1::block_data_order,
        format_output: sha256_format_output,
        initial_state: [
            u32x2!(0x67452301u32, 0xefcdab89u32),
            u32x2!(0x98badcfeu32, 0x10325476u32),
            u32x2!(0xc3d2e1f0u32, 0u32),
            0, 0, 0, 0, 0,
        ],
    };

    /// SHA-256 as specified in [FIPS 180-4].
    ///
    /// [FIPS 180-4]: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
    pub static SHA256: Algorithm = Algorithm {
        output_len: SHA256_OUTPUT_LEN,
        chaining_len: SHA256_OUTPUT_LEN,
        block_len: 512 / 8,
        len_len: 64 / 8,
        block_data_order: GFp_sha256_block_data_order,
        format_output: sha256_format_output,
        initial_state: [
            u32x2!(0x6a09e667u32, 0xbb67ae85u32),
            u32x2!(0x3c6ef372u32, 0xa54ff53au32),
            u32x2!(0x510e527fu32, 0x9b05688cu32),
            u32x2!(0x1f83d9abu32, 0x5be0cd19u32),
            0, 0, 0, 0,
        ],
    };

    /// SHA-384 as specified in [FIPS 180-4].
    ///
    /// [FIPS 180-4]: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
    pub static SHA384: Algorithm = Algorithm {
        output_len: SHA384_OUTPUT_LEN,
        chaining_len: SHA512_OUTPUT_LEN,
        block_len: SHA512_BLOCK_LEN,
        len_len: SHA512_LEN_LEN,
        block_data_order: GFp_sha512_block_data_order,
        format_output: sha512_format_output,
        initial_state: [
            0xcbbb9d5dc1059ed8,
            0x629a292a367cd507,
            0x9159015a3070dd17,
            0x152fecd8f70e5939,
            0x67332667ffc00b31,
            0x8eb44a8768581511,
            0xdb0c2e0d64f98fa7,
            0x47b5481dbefa4fa4,
        ],
    };

    /// SHA-512 as specified in [FIPS 180-4].
    ///
    /// [FIPS 180-4]: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
    pub static SHA512: Algorithm = Algorithm {
        output_len: SHA512_OUTPUT_LEN,
        chaining_len: SHA512_OUTPUT_LEN,
        block_len: SHA512_BLOCK_LEN,
        len_len: SHA512_LEN_LEN,
        block_data_order: GFp_sha512_block_data_order,
        format_output: sha512_format_output,
        initial_state: [
            0x6a09e667f3bcc908,
            0xbb67ae8584caa73b,
            0x3c6ef372fe94f82b,
            0xa54ff53a5f1d36f1,
            0x510e527fade682d1,
            0x9b05688c2b3e6c1f,
            0x1f83d9abfb41bd6b,
            0x5be0cd19137e2179,
        ],
    };

    /// SHA-512/256 as specified in [FIPS 180-4].
    ///
    /// This is *not* the same as just truncating the output of SHA-512, as
    /// SHA-512/256 has its own initial state distinct from SHA-512's initial
    /// state.
    ///
    /// [FIPS 180-4]: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
    pub static SHA512_256: Algorithm = Algorithm {
        output_len: SHA512_256_OUTPUT_LEN,
        chaining_len: SHA512_OUTPUT_LEN,
        block_len: SHA512_BLOCK_LEN,
        len_len: SHA512_LEN_LEN,
        block_data_order: GFp_sha512_block_data_order,
        format_output: sha512_format_output,
        initial_state: [
            0x22312194fc2bf72c,
            0x9f555fa3c84c64c2,
            0x2393b86b6f53b151,
            0x963877195940eabd,
            0x96283ee2a88effe3,
            0xbe5e1e2553863992,
            0x2b0199fc2c85b8aa,
            0x0eb72ddc81c52ca2,
        ],
    };

    // We use u64 to try to ensure 64-bit alignment/padding.
    type State = [u64; MAX_CHAINING_LEN / 8];

    type Output = [u64; MAX_OUTPUT_LEN / 8];

    /// The maximum block length (`Algorithm::block_len`) of all the algorithms in
    /// this module.
    pub const MAX_BLOCK_LEN: usize = 1024 / 8;

    /// The maximum output length (`Algorithm::output_len`) of all the algorithms
    /// in this module.
    pub const MAX_OUTPUT_LEN: usize = 512 / 8;

    /// The maximum chaining length (`Algorithm::chaining_len`) of all the
    /// algorithms in this module.
    pub const MAX_CHAINING_LEN: usize = MAX_OUTPUT_LEN;

    fn sha256_format_output(input: &State) -> Output {
        let input = &polyfill::slice::u64_as_u32(input)[..8];
        [u32x2!(input[0].to_be(), input[1].to_be()),
         u32x2!(input[2].to_be(), input[3].to_be()),
         u32x2!(input[4].to_be(), input[5].to_be()),
         u32x2!(input[6].to_be(), input[7].to_be()),
         0,
         0,
         0,
         0]
    }

    fn sha512_format_output(input: &State) -> Output {
        [input[0].to_be(),
         input[1].to_be(),
         input[2].to_be(),
         input[3].to_be(),
         input[4].to_be(),
         input[5].to_be(),
         input[6].to_be(),
         input[7].to_be()]
    }

    /// The length of the output of SHA-1, in bytes.
    pub const SHA1_OUTPUT_LEN: usize = sha1::OUTPUT_LEN;

    /// The length of the output of SHA-256, in bytes.
    pub const SHA256_OUTPUT_LEN: usize = 256 / 8;

    /// The length of the output of SHA-384, in bytes.
    pub const SHA384_OUTPUT_LEN: usize = 384 / 8;

    /// The length of the output of SHA-512, in bytes.
    pub const SHA512_OUTPUT_LEN: usize = 512 / 8;

    /// The length of the output of SHA-512/256, in bytes.
    pub const SHA512_256_OUTPUT_LEN: usize = 256 / 8;

    /// The length of a block for SHA-512-based algorithms, in bytes.
    const SHA512_BLOCK_LEN: usize = 1024 / 8;

    /// The length of the length field for SHA-512-based algorithms, in bytes.
    const SHA512_LEN_LEN: usize = 128 / 8;

    extern {
        fn GFp_sha256_block_data_order(state: &mut State, data: *const u8,
                                       num: c::size_t);
        fn GFp_sha512_block_data_order(state: &mut State, data: *const u8,
                                       num: c::size_t);
    }

    #[cfg(test)]
    pub mod test_util {
        use super::super::digest;

        pub static ALL_ALGORITHMS: [&'static digest::Algorithm; 5] = [
            &digest::SHA1,
            &digest::SHA256,
            &digest::SHA384,
            &digest::SHA512,
            &digest::SHA512_256,
        ];
    }

    #[cfg(test)]
    mod tests {

        mod max_input {
            use super::super::super::digest;

            macro_rules! max_input_tests {
                ( $algorithm_name:ident ) => {
                    #[allow(non_snake_case)]
                    mod $algorithm_name {
                        use super::super::super::super::digest;

                        #[test]
                        fn max_input_test() {
                            super::max_input_test(&digest::$algorithm_name);
                        }

                        #[test]
                        #[should_panic]
                        fn too_long_input_test_block() {
                            super::too_long_input_test_block(
                                &digest::$algorithm_name);
                        }

                        #[test]
                        #[should_panic]
                        fn too_long_input_test_byte() {
                            super::too_long_input_test_byte(
                                &digest::$algorithm_name);
                        }
                    }
                }
            }

            fn max_input_test(alg: &'static digest::Algorithm) {
                let mut context = nearly_full_context(alg);
                let next_input = vec![0u8; alg.block_len - 1];
                context.update(&next_input);
                let _ = context.finish(); // no panic
            }

            fn too_long_input_test_block(alg: &'static digest::Algorithm) {
                let mut context = nearly_full_context(alg);
                let next_input = vec![0u8; alg.block_len];
                context.update(&next_input);
                let _ = context.finish(); // should panic
            }

            fn too_long_input_test_byte(alg: &'static digest::Algorithm) {
                let mut context = nearly_full_context(alg);
                let next_input = vec![0u8; alg.block_len - 1];
                context.update(&next_input); // no panic
                context.update(&[0]);
                let _ = context.finish(); // should panic
            }

            fn nearly_full_context(alg: &'static digest::Algorithm)
                                   -> digest::Context {
                // All implementations currently support up to 2^64-1 bits
                // of input; according to the spec, SHA-384 and SHA-512
                // support up to 2^128-1, but that's not implemented yet.
                let max_bytes = 1u64 << (64 - 3);
                let max_blocks = max_bytes / (alg.block_len as u64);
                digest::Context {
                    algorithm: alg,
                    state: alg.initial_state,
                    completed_data_blocks: max_blocks - 1,
                    pending: [0u8; digest::MAX_BLOCK_LEN],
                    num_pending: 0,
                }
            }

            max_input_tests!(SHA1);
            max_input_tests!(SHA256);
            max_input_tests!(SHA384);
            max_input_tests!(SHA512);
        }
    }

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