diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1102277..6125b98 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -23,10 +23,7 @@ add_subdirectory(cruft/crypto)
 
 
 ###############################################################################
-add_executable (emory
-    emory.cpp
-)
-
-
-##-----------------------------------------------------------------------------
-target_link_libraries(emory cruft-crypto cruft-util)
+foreach (t emory emory-compare)
+    add_executable ("${t}" "${t}.cpp")
+    target_link_libraries("${t}" cruft-crypto cruft-util)
+endforeach()
diff --git a/emory-compare.cpp b/emory-compare.cpp
new file mode 100644
index 0000000..c4def70
--- /dev/null
+++ b/emory-compare.cpp
@@ -0,0 +1,176 @@
+/*
+ * 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/debug.hpp>
+#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>
+#include <iomanip>
+
+
+namespace emory {
+    using static_hash = cruft::crypto::hash::SHA1;
+
+    struct params {
+        std::size_t bits;
+        std::size_t window;
+        std::ptrdiff_t minimum;
+    };
+
+    struct chunk {
+        std::pair<off64_t, off64_t> offset;
+        static_hash::digest_t digest;
+
+        struct digest_equality {
+            bool operator() (chunk const &a, chunk const &b)
+            {
+                return a.digest == b.digest;
+            }
+        };
+
+
+        struct digest_comparator {
+            bool operator() (chunk const &a, chunk const &b)
+            {
+                return a.digest < b.digest;
+            }
+        };
+    };
+
+
+    std::ostream& operator<< (std::ostream &os, chunk const &val)
+    {
+        return os << "{ first: 0x"  << std::setw (8) << std::setfill ('0') << std::hex << val.offset.first
+                  << ", second: 0x" << std::setw (8) << std::setfill ('0') << std::hex << val.offset.second
+                  << " }" << std::dec;
+    }
+
+
+    struct map {
+        map (cruft::view<u08 const*> data, params const&);
+        std::vector<chunk> elements;
+    };
+
+
+    std::vector<chunk> common (map const &a, map const &b);
+}
+
+
+emory::map::map (cruft::view<u08 const *> data, const emory::params &p)
+{
+    using hash_type = cruft::hash::buzhash<u64>;
+    hash_type h (p.window, data);
+    auto remain = data.consume (p.window);
+
+    using digest_type = hash_type::digest_type ;
+    digest_type const mask = ~digest_type (0) >> (sizeof (digest_type) * 8 - p.bits);
+
+    for (u08 const *cursor = remain.begin (), *start = data.begin (); cursor != remain.end (); cursor++) {
+        auto const digest = h (cursor);
+
+        if (std::distance (start, cursor) < p.minimum)
+            continue;
+
+        if (unlikely (digest & mask))
+            continue;
+
+        cruft::view<u08 const*> const region { start, cursor };
+        start = cursor + 1;
+
+        elements.push_back ({
+            .offset = {
+                std::pair<std::size_t,std::size_t> {
+                    std::distance (data.begin (), region.begin ()),
+                    std::distance (data.begin (), region.end   ())
+                },
+            },
+            .digest = static_hash {} (region),
+        });
+    }
+}
+
+
+std::vector<emory::chunk>
+emory::common (emory::map const &a, emory::map const &b)
+{
+    CHECK (std::is_sorted (a.elements.begin (), a.elements.end (), emory::chunk::digest_comparator {}));
+    CHECK (std::is_sorted (b.elements.begin (), b.elements.end (), emory::chunk::digest_comparator {}));
+
+    std::vector<emory::chunk> res;
+
+    for (auto a_cursor = a.elements.begin (), b_cursor = b.elements.begin ();
+         a_cursor != a.elements.end () && b_cursor != b.elements.end ();
+         /* nothing */)
+    {
+        if (a_cursor->digest < b_cursor->digest) {
+            ++a_cursor;
+            continue;
+        }
+
+        if (b_cursor->digest < a_cursor->digest) {
+            ++b_cursor;
+            continue;
+        }
+
+        res.push_back (*a_cursor);
+        ++a_cursor;
+        ++b_cursor;
+    }
+
+    return res;
+}
+
+
+enum {
+    ARG_SELF,
+    ARG_BITS,
+    ARG_WINDOW,
+    ARGS_MINIMUM,
+    ARGS_TARGET,
+    ARGS_SOURCE,
+
+    NUM_ARGS,
+};
+
+
+int main (int argc, char const **argv)
+{
+    if (argc != NUM_ARGS) {
+        std::cerr << "usage: " << argv[ARG_SELF] << " <bits> <window> <minimum> <target> <source>\n";
+        return EXIT_FAILURE;
+    }
+
+    emory::params const p {
+        .window = cruft::parse::from_string<std::size_t> (argv[ARG_WINDOW]),
+        .bits   = cruft::parse::from_string<std::size_t> (argv[ARG_BITS  ]),
+        .minimum = cruft::parse::from_string<std::ptrdiff_t> (argv[ARGS_MINIMUM]),
+    };
+
+    emory::map target (cruft::mapped_file (argv[ARGS_TARGET]), p);
+    emory::map source (cruft::mapped_file (argv[ARGS_SOURCE]), p);
+
+    std::clog << "Hashing target\n";
+    std::sort (target.elements.begin (), target.elements.end (), emory::chunk::digest_comparator {});
+    std::clog << "Hashing source\n";
+    std::sort (source.elements.begin (), source.elements.end (), emory::chunk::digest_comparator {});
+
+    std::clog << "Finding common\n";
+    auto const &found = common (target, source);
+    std::size_t total = 0;
+    for (auto const &i: found) {
+        std::cout << i << '\n';
+        total += i.offset.second - i.offset.first;
+    }
+
+    std::cout << "Found " << found.size () << " chunks of " << total << " bytes\n";
+}