extract some basic code from libcryptonote_core into libcryptonote_basic

1 files changed, 165 insertions, 0 deletions

diff --git a/src/cryptonote_basic/difficulty.cpp b/src/cryptonote_basic/difficulty.cpp
new file mode 100644
index 000000000..1c5b9cfbd
--- /dev/null
+++ b/src/cryptonote_basic/difficulty.cpp
@@ -0,0 +1,165 @@
+// 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
+
+#include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+#include <vector>
+
+#include "common/int-util.h"
+#include "crypto/hash.h"
+#include "cryptonote_config.h"
+#include "difficulty.h"
+
+#undef MONERO_DEFAULT_LOG_CATEGORY
+#define MONERO_DEFAULT_LOG_CATEGORY "difficulty"
+
+namespace cryptonote {
+
+  using std::size_t;
+  using std::uint64_t;
+  using std::vector;
+
+#if defined(__x86_64__)
+  static inline void mul(uint64_t a, uint64_t b, uint64_t &low, uint64_t &high) {
+    low = mul128(a, b, &high);
+  }
+
+#else
+
+  static inline void mul(uint64_t a, uint64_t b, uint64_t &low, uint64_t &high) {
+    // __int128 isn't part of the standard, so the previous function wasn't portable. mul128() in Windows is fine,
+    // but this portable function should be used elsewhere. Credit for this function goes to latexi95.
+
+    uint64_t aLow = a & 0xFFFFFFFF;
+    uint64_t aHigh = a >> 32;
+    uint64_t bLow = b & 0xFFFFFFFF;
+    uint64_t bHigh = b >> 32;
+
+    uint64_t res = aLow * bLow;
+    uint64_t lowRes1 = res & 0xFFFFFFFF;
+    uint64_t carry = res >> 32;
+
+    res = aHigh * bLow + carry;
+    uint64_t highResHigh1 = res >> 32;
+    uint64_t highResLow1 = res & 0xFFFFFFFF;
+
+    res = aLow * bHigh;
+    uint64_t lowRes2 = res & 0xFFFFFFFF;
+    carry = res >> 32;
+
+    res = aHigh * bHigh + carry;
+    uint64_t highResHigh2 = res >> 32;
+    uint64_t highResLow2 = res & 0xFFFFFFFF;
+
+    //Addition
+
+    uint64_t r = highResLow1 + lowRes2;
+    carry = r >> 32;
+    low = (r << 32) | lowRes1;
+    r = highResHigh1 + highResLow2 + carry;
+    uint64_t d3 = r & 0xFFFFFFFF;
+    carry = r >> 32;
+    r = highResHigh2 + carry;
+    high = d3 | (r << 32);
+  }
+
+#endif
+
+  static inline bool cadd(uint64_t a, uint64_t b) {
+    return a + b < a;
+  }
+
+  static inline bool cadc(uint64_t a, uint64_t b, bool c) {
+    return a + b < a || (c && a + b == (uint64_t) -1);
+  }
+
+  bool check_hash(const crypto::hash &hash, difficulty_type difficulty) {
+    uint64_t low, high, top, cur;
+    // First check the highest word, this will most likely fail for a random hash.
+    mul(swap64le(((const uint64_t *) &hash)[3]), difficulty, top, high);
+    if (high != 0) {
+      return false;
+    }
+    mul(swap64le(((const uint64_t *) &hash)[0]), difficulty, low, cur);
+    mul(swap64le(((const uint64_t *) &hash)[1]), difficulty, low, high);
+    bool carry = cadd(cur, low);
+    cur = high;
+    mul(swap64le(((const uint64_t *) &hash)[2]), difficulty, low, high);
+    carry = cadc(cur, low, carry);
+    carry = cadc(high, top, carry);
+    return !carry;
+  }
+
+  difficulty_type next_difficulty(std::vector<std::uint64_t> timestamps, std::vector<difficulty_type> cumulative_difficulties, size_t target_seconds) {
+
+    if(timestamps.size() > DIFFICULTY_WINDOW)
+    {
+      timestamps.resize(DIFFICULTY_WINDOW);
+      cumulative_difficulties.resize(DIFFICULTY_WINDOW);
+    }
+
+
+    size_t length = timestamps.size();
+    assert(length == cumulative_difficulties.size());
+    if (length <= 1) {
+      return 1;
+    }
+    static_assert(DIFFICULTY_WINDOW >= 2, "Window is too small");
+    assert(length <= DIFFICULTY_WINDOW);
+    sort(timestamps.begin(), timestamps.end());
+    size_t cut_begin, cut_end;
+    static_assert(2 * DIFFICULTY_CUT <= DIFFICULTY_WINDOW - 2, "Cut length is too large");
+    if (length <= DIFFICULTY_WINDOW - 2 * DIFFICULTY_CUT) {
+      cut_begin = 0;
+      cut_end = length;
+    } else {
+      cut_begin = (length - (DIFFICULTY_WINDOW - 2 * DIFFICULTY_CUT) + 1) / 2;
+      cut_end = cut_begin + (DIFFICULTY_WINDOW - 2 * DIFFICULTY_CUT);
+    }
+    assert(/*cut_begin >= 0 &&*/ cut_begin + 2 <= cut_end && cut_end <= length);
+    uint64_t time_span = timestamps[cut_end - 1] - timestamps[cut_begin];
+    if (time_span == 0) {
+      time_span = 1;
+    }
+    difficulty_type total_work = cumulative_difficulties[cut_end - 1] - cumulative_difficulties[cut_begin];
+    assert(total_work > 0);
+    uint64_t low, high;
+    mul(total_work, target_seconds, low, high);
+    // blockchain errors "difficulty overhead" if this function returns zero.
+    // TODO: consider throwing an exception instead
+    if (high != 0 || low + time_span - 1 < low) {
+      return 0;
+    }
+    return (low + time_span - 1) / time_span;
+  }
+
+}