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277 lines
11 KiB
277 lines
11 KiB
// Copyright (c) 2014-2018, The Monero Project
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//
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without modification, are
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// permitted provided that the following conditions are met:
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//
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// 1. Redistributions of source code must retain the above copyright notice, this list of
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// conditions and the following disclaimer.
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//
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// 2. Redistributions in binary form must reproduce the above copyright notice, this list
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// of conditions and the following disclaimer in the documentation and/or other
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// materials provided with the distribution.
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//
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// 3. Neither the name of the copyright holder nor the names of its contributors may be
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// used to endorse or promote products derived from this software without specific
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// prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
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// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
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// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
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// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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//
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// Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers
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#include <algorithm>
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#include <cassert>
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#include <cstddef>
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#include <cstdint>
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#include <vector>
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#include <boost/math/special_functions/round.hpp>
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#include "common/int-util.h"
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#include "crypto/hash.h"
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#include "cryptonote_config.h"
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#include "difficulty.h"
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#undef MONERO_DEFAULT_LOG_CATEGORY
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#define MONERO_DEFAULT_LOG_CATEGORY "difficulty"
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namespace cryptonote {
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using std::size_t;
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using std::uint64_t;
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using std::vector;
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#if defined(__x86_64__)
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static inline void mul(uint64_t a, uint64_t b, uint64_t &low, uint64_t &high) {
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low = mul128(a, b, &high);
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}
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#else
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static inline void mul(uint64_t a, uint64_t b, uint64_t &low, uint64_t &high) {
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// __int128 isn't part of the standard, so the previous function wasn't portable. mul128() in Windows is fine,
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// but this portable function should be used elsewhere. Credit for this function goes to latexi95.
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uint64_t aLow = a & 0xFFFFFFFF;
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uint64_t aHigh = a >> 32;
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uint64_t bLow = b & 0xFFFFFFFF;
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uint64_t bHigh = b >> 32;
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uint64_t res = aLow * bLow;
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uint64_t lowRes1 = res & 0xFFFFFFFF;
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uint64_t carry = res >> 32;
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res = aHigh * bLow + carry;
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uint64_t highResHigh1 = res >> 32;
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uint64_t highResLow1 = res & 0xFFFFFFFF;
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res = aLow * bHigh;
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uint64_t lowRes2 = res & 0xFFFFFFFF;
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carry = res >> 32;
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res = aHigh * bHigh + carry;
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uint64_t highResHigh2 = res >> 32;
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uint64_t highResLow2 = res & 0xFFFFFFFF;
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//Addition
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uint64_t r = highResLow1 + lowRes2;
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carry = r >> 32;
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low = (r << 32) | lowRes1;
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r = highResHigh1 + highResLow2 + carry;
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uint64_t d3 = r & 0xFFFFFFFF;
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carry = r >> 32;
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r = highResHigh2 + carry;
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high = d3 | (r << 32);
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}
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#endif
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static inline bool cadd(uint64_t a, uint64_t b) {
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return a + b < a;
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}
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static inline bool cadc(uint64_t a, uint64_t b, bool c) {
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return a + b < a || (c && a + b == (uint64_t) -1);
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}
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bool check_hash(const crypto::hash &hash, difficulty_type difficulty) {
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uint64_t low, high, top, cur;
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// First check the highest word, this will most likely fail for a random hash.
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mul(swap64le(((const uint64_t *) &hash)[3]), difficulty, top, high);
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if (high != 0) {
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return false;
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}
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mul(swap64le(((const uint64_t *) &hash)[0]), difficulty, low, cur);
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mul(swap64le(((const uint64_t *) &hash)[1]), difficulty, low, high);
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bool carry = cadd(cur, low);
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cur = high;
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mul(swap64le(((const uint64_t *) &hash)[2]), difficulty, low, high);
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carry = cadc(cur, low, carry);
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carry = cadc(high, top, carry);
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return !carry;
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}
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difficulty_type next_difficulty(std::vector<std::uint64_t> timestamps, std::vector<difficulty_type> cumulative_difficulties, size_t target_seconds) {
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if(timestamps.size() > DIFFICULTY_WINDOW)
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{
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timestamps.resize(DIFFICULTY_WINDOW);
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cumulative_difficulties.resize(DIFFICULTY_WINDOW);
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}
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size_t length = timestamps.size();
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assert(length == cumulative_difficulties.size());
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if (length <= 1) {
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return 1;
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}
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static_assert(DIFFICULTY_WINDOW >= 2, "Window is too small");
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assert(length <= DIFFICULTY_WINDOW);
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sort(timestamps.begin(), timestamps.end());
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size_t cut_begin, cut_end;
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static_assert(2 * DIFFICULTY_CUT <= DIFFICULTY_WINDOW - 2, "Cut length is too large");
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if (length <= DIFFICULTY_WINDOW - 2 * DIFFICULTY_CUT) {
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cut_begin = 0;
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cut_end = length;
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} else {
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cut_begin = (length - (DIFFICULTY_WINDOW - 2 * DIFFICULTY_CUT) + 1) / 2;
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cut_end = cut_begin + (DIFFICULTY_WINDOW - 2 * DIFFICULTY_CUT);
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}
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assert(/*cut_begin >= 0 &&*/ cut_begin + 2 <= cut_end && cut_end <= length);
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uint64_t time_span = timestamps[cut_end - 1] - timestamps[cut_begin];
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if (time_span == 0) {
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time_span = 1;
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}
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difficulty_type total_work = cumulative_difficulties[cut_end - 1] - cumulative_difficulties[cut_begin];
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assert(total_work > 0);
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uint64_t low, high;
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mul(total_work, target_seconds, low, high);
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// blockchain errors "difficulty overhead" if this function returns zero.
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// TODO: consider throwing an exception instead
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if (high != 0 || low + time_span - 1 < low) {
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return 0;
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}
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return (low + time_span - 1) / time_span;
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}
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// LWMA difficulty algorithm
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// Background: https://github.com/zawy12/difficulty-algorithms/issues/3
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// Copyright (c) 2017-2018 Zawy (pseudocode)
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// MIT license http://www.opensource.org/licenses/mit-license.php
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// Copyright (c) 2018 Wownero Inc., a Monero Enterprise Alliance partner company
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// Copyright (c) 2018 The Karbowanec developers (initial code)
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// Copyright (c) 2018 Haven Protocol (refinements)
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// Degnr8, Karbowanec, Masari, Bitcoin Gold, Bitcoin Candy, and Haven have contributed.
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// This algorithm is: next_difficulty = harmonic_mean(Difficulties) * T / LWMA(Solvetimes)
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// The harmonic_mean(Difficulties) = 1/average(Targets) so it is also:
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// next_target = avg(Targets) * LWMA(Solvetimes) / T.
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// This is "the best algorithm" because it has lowest root-mean-square error between
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// needed & actual difficulty during hash attacks while having the lowest standard
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// deviation during stable hashrate. That is, it's the fastest for a given stability and vice versa.
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// Do not use "if solvetime < 1 then solvetime = 1" which allows a catastrophic exploit.
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// Do not sort timestamps. "Solvetimes" and "LWMA" variables must allow negatives.
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// Do not use MTP as most recent block. Do not use (POW)Limits, filtering, or tempering.
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// Do not forget to set N (aka DIFFICULTY_WINDOW in Cryptonote) to recommendation below.
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// The nodes' future time limit (FTL) aka CRYPTONOTE_BLOCK_FUTURE_TIME_LIMIT needs to
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// be reduced from 60*60*2 to 500 seconds to prevent timestamp manipulation from miner's with
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// > 50% hash power. If this is too small, it can be increased to 1000 at a cost in protection.
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// Cryptonote clones: #define DIFFICULTY_BLOCKS_COUNT_V2 DIFFICULTY_WINDOW_V2 + 1
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difficulty_type next_difficulty_v2(std::vector<std::uint64_t> timestamps, std::vector<difficulty_type> cumulative_difficulties, size_t target_seconds) {
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const int64_t T = static_cast<int64_t>(target_seconds);
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size_t N = DIFFICULTY_WINDOW_V2;
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// Return a difficulty of 1 for first 3 blocks if it's the start of the chain.
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if (timestamps.size() < 4) {
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return 1;
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}
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// Otherwise, use a smaller N if the start of the chain is less than N+1.
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else if ( timestamps.size() < N+1 ) {
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N = timestamps.size() - 1;
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}
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// Otherwise make sure timestamps and cumulative_difficulties are correct size.
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else {
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timestamps.resize(N+1);
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cumulative_difficulties.resize(N+1);
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}
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// To get an average solvetime to within +/- ~0.1%, use an adjustment factor.
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// adjust=0.999 for 80 < N < 120(?)
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const double adjust = 0.998;
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// The divisor k normalizes the LWMA sum to a standard LWMA.
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const double k = N * (N + 1) / 2;
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double LWMA(0), sum_inverse_D(0), harmonic_mean_D(0), nextDifficulty(0);
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int64_t solveTime(0);
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uint64_t difficulty(0), next_difficulty(0);
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// Loop through N most recent blocks. N is most recently solved block.
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for (size_t i = 1; i <= N; i++) {
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solveTime = static_cast<int64_t>(timestamps[i]) - static_cast<int64_t>(timestamps[i - 1]);
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solveTime = std::min<int64_t>((T * 7), std::max<int64_t>(solveTime, (-7 * T)));
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difficulty = cumulative_difficulties[i] - cumulative_difficulties[i - 1];
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LWMA += (int64_t)(solveTime * i) / k;
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sum_inverse_D += 1 / static_cast<double>(difficulty);
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}
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harmonic_mean_D = N / sum_inverse_D;
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// Keep LWMA sane in case something unforeseen occurs.
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if (static_cast<int64_t>(boost::math::round(LWMA)) < T / 20)
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LWMA = static_cast<double>(T / 20);
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nextDifficulty = harmonic_mean_D * T / LWMA * adjust;
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// No limits should be employed, but this is correct way to employ a 20% symmetrical limit:
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// nextDifficulty=max(previous_Difficulty*0.8,min(previous_Difficulty/0.8, next_Difficulty));
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next_difficulty = static_cast<uint64_t>(nextDifficulty);
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return next_difficulty;
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}
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// LWMA-2 difficulty algorithm
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// Copyright (c) 2017-2018 Zawy, MIT License
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// See commented version in https://github.com/zawy12/difficulty-algorithms/issues/3
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// for required config file changes.
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difficulty_type next_difficulty_v3(std::vector<std::uint64_t> timestamps, std::vector<difficulty_type> cumulative_difficulties) {
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int64_t T = DIFFICULTY_TARGET_V2;
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int64_t N = DIFFICULTY_WINDOW_V2;
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int64_t FTL = CRYPTONOTE_BLOCK_FUTURE_TIME_LIMIT_V3;
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int64_t L(0), ST, sum_3_ST(0), next_D, prev_D;
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// TODO: change initial_difficulty_guess before v9 mainnet hard fork
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// if ( height >= fork_height && height <= fork_height+N ) { return difficulty_guess; }
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uint64_t initial_difficulty_guess = 100;
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if (timestamps.size() <= 6 ) { return initial_difficulty_guess; }
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else if ( timestamps.size() < static_cast<uint64_t>(N +1) ) { N=timestamps.size()-1; }
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for ( int64_t i = 1; i <= N; i++) {
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ST = std::max(-FTL, std::min( (int64_t)(timestamps[i]) - (int64_t)(timestamps[i-1]), 6*T));
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L += ST * i ;
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if ( i > N-3 ) { sum_3_ST += ST; }
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}
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next_D = ((int64_t)(cumulative_difficulties[N] - cumulative_difficulties[0])*T*(N+1)*99)/(100*2*L);
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prev_D = cumulative_difficulties[N] - cumulative_difficulties[N-1];
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next_D = std::max((prev_D*67)/100, std::min( next_D, (prev_D*150)/100));
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if ( sum_3_ST < (8*T)/10) { next_D = (prev_D*110)/100; }
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return static_cast<uint64_t>(next_D);
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}
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}
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