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    // Copyright 2015-2016 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.

    //! Constant-time operations.

    use {c, error};

    /// Returns `Ok(())` if `a == b` and `Err(error::Unspecified)` otherwise.
    /// The comparison of `a` and `b` is done in constant time with respect to the
    /// contents of each, but NOT in constant time with respect to the lengths of
    /// `a` and `b`.
    pub fn verify_slices_are_equal(a: &[u8], b: &[u8])
                                   -> Result<(), error::Unspecified> {
        if a.len() != b.len() {
            return Err(error::Unspecified);
        }
        let result = unsafe { GFp_memcmp(a.as_ptr(), b.as_ptr(), a.len()) };
        match result {
            0 => Ok(()),
            _ => Err(error::Unspecified),
        }
    }

    extern {
        fn GFp_memcmp(a: *const u8, b: *const u8, len: c::size_t) -> c::int;
    }

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