69 lines
2 KiB
Go
69 lines
2 KiB
Go
// Copyright (c) 2017-2026 Lethean (https://lt.hn)
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//
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// Licensed under the European Union Public Licence (EUPL) version 1.2.
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// SPDX-License-Identifier: EUPL-1.2
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package chain
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import (
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"math/big"
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"forge.lthn.ai/core/go-blockchain/config"
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"forge.lthn.ai/core/go-blockchain/difficulty"
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)
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// NextDifficulty computes the expected difficulty for the block at the given
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// height, using the LWMA algorithm over stored block history.
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//
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// The genesis block (height 0) is excluded from the difficulty window,
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// matching the C++ daemon's load_targetdata_cache which skips index 0.
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//
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// The target block time depends on the hardfork schedule: 120s pre-HF2,
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// 240s post-HF2 (matching DIFFICULTY_POW_TARGET_HF6 in the C++ source).
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func (c *Chain) NextDifficulty(height uint64, forks []config.HardFork) (uint64, error) {
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if height == 0 {
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return 1, nil
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}
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// LWMA needs N+1 entries (N solve-time intervals).
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// Start from height 1 — genesis is excluded from the difficulty window.
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maxLookback := difficulty.LWMAWindow + 1
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lookback := min(height, maxLookback) // height excludes genesis since we start from 1
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// Start from max(1, height - lookback) to exclude genesis.
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startHeight := height - lookback
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if startHeight == 0 {
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startHeight = 1
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lookback = height - 1
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}
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if lookback == 0 {
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return 1, nil
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}
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count := int(lookback)
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timestamps := make([]uint64, count)
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cumulDiffs := make([]*big.Int, count)
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for i := range count {
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meta, err := c.getBlockMeta(startHeight + uint64(i))
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if err != nil {
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// Fewer blocks than expected — use what we have.
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timestamps = timestamps[:i]
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cumulDiffs = cumulDiffs[:i]
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break
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}
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timestamps[i] = meta.Timestamp
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cumulDiffs[i] = new(big.Int).SetUint64(meta.CumulativeDiff)
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}
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// Determine the target block time based on hardfork status.
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// HF2 doubles the target from 120s to 240s.
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target := config.DifficultyPowTarget
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if config.IsHardForkActive(forks, config.HF2, height) {
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target = config.DifficultyPowTargetHF6
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}
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result := difficulty.NextDifficulty(timestamps, cumulDiffs, target)
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return result.Uint64(), nil
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}
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