github.com/SmartMeshFoundation/Spectrum@v0.0.0-20220621030607-452a266fee1e/consensus/ethash/algorithm_go1.8.go (about)

     1  // Copyright 2017 The Spectrum Authors
     2  // This file is part of the Spectrum library.
     3  //
     4  // The Spectrum library is free software: you can redistribute it and/or modify
     5  // it under the terms of the GNU Lesser General Public License as published by
     6  // the Free Software Foundation, either version 3 of the License, or
     7  // (at your option) any later version.
     8  //
     9  // The Spectrum library is distributed in the hope that it will be useful,
    10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    12  // GNU Lesser General Public License for more details.
    13  //
    14  // You should have received a copy of the GNU Lesser General Public License
    15  // along with the Spectrum library. If not, see <http://www.gnu.org/licenses/>.
    16  
    17  // +build go1.8
    18  
    19  package ethash
    20  
    21  import "math/big"
    22  
    23  // cacheSize calculates and returns the size of the ethash verification cache that
    24  // belongs to a certain block number. The cache size grows linearly, however, we
    25  // always take the highest prime below the linearly growing threshold in order to
    26  // reduce the risk of accidental regularities leading to cyclic behavior.
    27  func cacheSize(block uint64) uint64 {
    28  	// If we have a pre-generated value, use that
    29  	epoch := int(block / epochLength)
    30  	if epoch < len(cacheSizes) {
    31  		return cacheSizes[epoch]
    32  	}
    33  	// No known cache size, calculate manually (sanity branch only)
    34  	size := cacheInitBytes + cacheGrowthBytes*uint64(epoch) - hashBytes
    35  	for !new(big.Int).SetUint64(size / hashBytes).ProbablyPrime(1) { // Always accurate for n < 2^64
    36  		size -= 2 * hashBytes
    37  	}
    38  	return size
    39  }
    40  
    41  // datasetSize calculates and returns the size of the ethash mining dataset that
    42  // belongs to a certain block number. The dataset size grows linearly, however, we
    43  // always take the highest prime below the linearly growing threshold in order to
    44  // reduce the risk of accidental regularities leading to cyclic behavior.
    45  func datasetSize(block uint64) uint64 {
    46  	// If we have a pre-generated value, use that
    47  	epoch := int(block / epochLength)
    48  	if epoch < len(datasetSizes) {
    49  		return datasetSizes[epoch]
    50  	}
    51  	// No known dataset size, calculate manually (sanity branch only)
    52  	size := datasetInitBytes + datasetGrowthBytes*uint64(epoch) - mixBytes
    53  	for !new(big.Int).SetUint64(size / mixBytes).ProbablyPrime(1) { // Always accurate for n < 2^64
    54  		size -= 2 * mixBytes
    55  	}
    56  	return size
    57  }