emory/emory.cpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2013 Danny Robson <danny@nerdcruft.net>
 */

#include <cruft/util/hash/buzhash.hpp>
#include <cruft/util/io.hpp>
#include <cruft/util/parse/value.hpp>

#include <cruft/crypto/hash/sha1.hpp>

#include <algorithm>
#include <iostream>


struct chunk {
    cruft::view<u08 const*> data;
    cruft::crypto::hash::SHA1::digest_t digest;
};

struct digest_equality {
    bool operator() (chunk const &a, chunk const &b)
    {
        return a.digest == b.digest;
    }
};


enum {
    ARG_SELF,
    ARG_BITS,
    ARG_WINDOW,
    ARGS_INPUT,

    NUM_ARGS,
};


int main (int argc, char const **argv)
{
    if (argc != NUM_ARGS) {
        std::cerr << "usage: " << argv[ARG_SELF] << " <bits> <window> <input>\n";
        return EXIT_FAILURE;
    }

    auto const window = cruft::parse::from_string<std::size_t> (argv[ARG_WINDOW]);
    auto const bits   = cruft::parse::from_string<std::size_t> (argv[ARG_BITS  ]);

    cruft::mapped_file src (argv[ARGS_INPUT]);
    cruft::view bytes (src);

    using hash_type = cruft::hash::buzhash<u64>;
    hash_type h (window, bytes);
    bytes = bytes.consume (window);

    using digest_type = hash_type::digest_type ;
    digest_type const mask = ~digest_type (0) >> (sizeof (digest_type) * 8 - bits);

    std::vector<chunk> chunks;

    for (u08 const *cursor = bytes.begin (), *start = src.data (); cursor != bytes.end (); cursor++) {
        auto const res = h (cursor);

        if (res & mask)
            continue;

        cruft::view<u08 const*> const region { start, cursor };
        start = cursor + 1;

        chunks.push_back ({
            .data = region,
            .digest = cruft::crypto::hash::SHA1 {} (region),
        });
    }

    std::sort (
        std::begin (chunks),
        std::end   (chunks),
        [] (auto const &a, auto const &b)
    {
        return a.digest < b.digest;
    });

    std::size_t reduction = 0;
    for (auto cursor = chunks.begin (); cursor != chunks.end (); ++cursor) {
        auto first_match = std::adjacent_find (
            cursor, chunks.end (),
            digest_equality {}
        );

        if (first_match == chunks.end ())
            break;

        auto last_match = std::find_if_not (
            first_match,
            chunks.end (),
            [&first_match] (auto const &i)
        {
            return i.digest == first_match->digest;
        });

        auto const count = std::distance (first_match, last_match);
        auto const size  = first_match->data.size ();
        std::cout << count << " duplicates of " << size << " bytes\n";
        reduction += (count - 1) * size;

        cursor = last_match;
    }

    std::cout << chunks.size () << " chunks found\n";
    std::cout << float (reduction) / src.size () << " reduction\n";
}