extract some basic code from libcryptonote_core into libcryptonote_basic

src/cryptonote_basic/difficulty.h

@@ -0,0 +1,56 @@
+// Copyright (c) 2014-2016, The Monero Project
+// 
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+// 
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+// 
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+// 
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+// 
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+// 
+// Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers
+
+#pragma once
+
+#include <cstdint>
+#include <vector>
+
+#include "crypto/hash.h"
+
+namespace cryptonote
+{
+    typedef std::uint64_t difficulty_type;
+
+    /**
+     * @brief checks if a hash fits the given difficulty
+     *
+     * The hash passes if (hash * difficulty) < 2^192.
+     * Phrased differently, if (hash * difficulty) fits without overflow into
+     * the least significant 192 bits of the 256 bit multiplication result.
+     *
+     * @param hash the hash to check
+     * @param difficulty the difficulty to check against
+     *
+     * @return true if valid, else false
+     */
+    bool check_hash(const crypto::hash &hash, difficulty_type difficulty);
+    difficulty_type next_difficulty(std::vector<std::uint64_t> timestamps, std::vector<difficulty_type> cumulative_difficulties, size_t target_seconds);
+}