简介

共识机制是区块链研究领域的热点，比特币采用的是POW机制，通过大量的算例来解决一个困难性问题从而产生新的区块，而正因为产生新的区块需要大量的算例，网络中的节点才相信最长的链是最可靠的，这种最长链原则也是比特币中共识的原理。

文件名 pramas.h

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class Consensus

Consensus

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namespace Consensus {

enum DeploymentPos
{
    DEPLOYMENT_TESTDUMMY,
    DEPLOYMENT_CSV, // Deployment of BIP68, BIP112, and BIP113.
    DEPLOYMENT_SEGWIT, // Deployment of BIP141, BIP143, and BIP147.
    // NOTE: Also add new deployments to VersionBitsDeploymentInfo in versionbits.cpp
    MAX_VERSION_BITS_DEPLOYMENTS
};

/**
 * Struct for each individual consensus rule change using BIP9.
 */
struct BIP9Deployment {
    /** Bit position to select the particular bit in nVersion. */
    int bit;
    /** Start MedianTime for version bits miner confirmation. Can be a date in the past */
    int64_t nStartTime;
    /** Timeout/expiry MedianTime for the deployment attempt. */
    int64_t nTimeout;

    /** Constant for nTimeout very far in the future. */
    static constexpr int64_t NO_TIMEOUT = std::numeric_limits<int64_t>::max();

    /** Special value for nStartTime indicating that the deployment is always active.
     *  This is useful for testing, as it means tests don't need to deal with the activation
     *  process (which takes at least 3 BIP9 intervals). Only tests that specifically test the
     *  behaviour during activation cannot use this. */
    static constexpr int64_t ALWAYS_ACTIVE = -1;
};

/**
 * Parameters that influence chain consensus.
 * 影响共识的参数
 */
struct Params {
    uint256 hashGenesisBlock;   //创世区块的哈希
    int nSubsidyHalvingInterval;    //奖励减半的时间间隔
    /** Block height at which BIP16 becomes active */
    int BIP16Height;    //区块高度
    /** Block height and hash at which BIP34 becomes active */
    int BIP34Height;    //区块Hash
    uint256 BIP34Hash;
    /** Block height at which BIP65 becomes active */
    int BIP65Height;
    /** Block height at which BIP66 becomes active */
    int BIP66Height;
    /**
     * Minimum blocks including miner confirmation of the total of 2016 blocks in a retargeting period,
     * (nPowTargetTimespan / nPowTargetSpacing) which is also used for BIP9 deployments.
     * Examples: 1916 for 95%, 1512 for testchains.
     * 在2016个区块中至少要有多少个区块被矿工确认，规则改变才能生效
     * 在BIP9上线时还使用(nPowTargetTimespan / nPowTargetSpacing)值
     */
    uint32_t nRuleChangeActivationThreshold;
    uint32_t nMinerConfirmationWindow;
    BIP9Deployment vDeployments[MAX_VERSION_BITS_DEPLOYMENTS];
    /** Proof of work parameters */
    // POW参数
    uint256 powLimit;   //难度
    bool fPowAllowMinDifficultyBlocks;//是否允许最低难度
    bool fPowNoRetargeting; //不调整难度
    int64_t nPowTargetSpacing; //区块产生平均时间
    int64_t nPowTargetTimespan; //难度调整时间
    int64_t DifficultyAdjustmentInterval() const { return nPowTargetTimespan / nPowTargetSpacing; }
    uint256 nMinimumChainWork;  //当前难度最小值
    uint256 defaultAssumeValid; //在此区块之前的区块都认为是有效的
};
} // namespace Consensus