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// Copyright 2021 The Grin Developers
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//! All the rules required for a cryptocurrency to have reach consensus across
//! the whole network are complex and hard to completely isolate. Some can be
//! simple parameters (like block reward), others complex algorithms (like
//! Merkle sum trees or reorg rules). However, as long as they're simple
//! enough, consensus-relevant constants and short functions should be kept
//! here.
use crate::core::block::HeaderVersion;
use crate::core::hash::Hash;
use crate::global;
use crate::pow::Difficulty;
use std::cmp::{max, min};
/// A grin is divisible to 10^9, following the SI prefixes
pub const GRIN_BASE: u64 = 1_000_000_000;
/// Milligrin, a thousand of a grin
pub const MILLI_GRIN: u64 = GRIN_BASE / 1_000;
/// Microgrin, a thousand of a milligrin
pub const MICRO_GRIN: u64 = MILLI_GRIN / 1_000;
/// Nanogrin, smallest unit, takes a billion to make a grin
pub const NANO_GRIN: u64 = 1;
/// Block interval, in seconds, the network will tune its next_target for. Note
/// that we may reduce this value in the future as we get more data on mining
/// with Cuckoo Cycle, networks improve and block propagation is optimized
/// (adjusting the reward accordingly).
pub const BLOCK_TIME_SEC: u64 = 60;
/// The block subsidy amount, one grin per second on average
pub const REWARD: u64 = BLOCK_TIME_SEC * GRIN_BASE;
/// Actual block reward for a given total fee amount
pub fn reward(fee: u64) -> u64 {
REWARD.saturating_add(fee)
}
/// an hour in seconds
pub const HOUR_SEC: u64 = 60 * 60;
/// Nominal height for standard time intervals, hour is 60 blocks
pub const HOUR_HEIGHT: u64 = HOUR_SEC / BLOCK_TIME_SEC;
/// A day is 1440 blocks
pub const DAY_HEIGHT: u64 = 24 * HOUR_HEIGHT;
/// A week is 10_080 blocks
pub const WEEK_HEIGHT: u64 = 7 * DAY_HEIGHT;
/// A year is 524_160 blocks
pub const YEAR_HEIGHT: u64 = 52 * WEEK_HEIGHT;
/// Number of blocks before a coinbase matures and can be spent
pub const COINBASE_MATURITY: u64 = DAY_HEIGHT;
/// Target ratio of secondary proof of work to primary proof of work,
/// as a function of block height (time). Starts at 90% losing a percent
/// approximately every week. Represented as an integer between 0 and 100.
pub fn secondary_pow_ratio(height: u64) -> u64 {
90u64.saturating_sub(height / (2 * YEAR_HEIGHT / 90))
}
/// Cuckoo-cycle proof size (cycle length)
pub const PROOFSIZE: usize = 42;
/// Default Cuckatoo Cycle edge_bits, used for mining and validating.
pub const DEFAULT_MIN_EDGE_BITS: u8 = 31;
/// Cuckaroo* proof-of-work edge_bits, meant to be ASIC resistant.
pub const SECOND_POW_EDGE_BITS: u8 = 29;
/// Original reference edge_bits to compute difficulty factors for higher
/// Cuckoo graph sizes, changing this would hard fork
pub const BASE_EDGE_BITS: u8 = 24;
/// Default number of blocks in the past when cross-block cut-through will start
/// happening. Needs to be long enough to not overlap with a long reorg.
/// Rational
/// behind the value is the longest bitcoin fork was about 30 blocks, so 5h. We
/// add an order of magnitude to be safe and round to 7x24h of blocks to make it
/// easier to reason about.
pub const CUT_THROUGH_HORIZON: u32 = WEEK_HEIGHT as u32;
/// Default number of blocks in the past to determine the height where we request
/// a txhashset (and full blocks from). Needs to be long enough to not overlap with
/// a long reorg.
/// Rational behind the value is the longest bitcoin fork was about 30 blocks, so 5h.
/// We add an order of magnitude to be safe and round to 2x24h of blocks to make it
/// easier to reason about.
pub const STATE_SYNC_THRESHOLD: u32 = 2 * DAY_HEIGHT as u32;
/// Weight of an input when counted against the max block weight capacity
pub const INPUT_WEIGHT: u64 = 1;
/// Weight of an output when counted against the max block weight capacity
pub const OUTPUT_WEIGHT: u64 = 21;
/// Weight of a kernel when counted against the max block weight capacity
pub const KERNEL_WEIGHT: u64 = 3;
/// Total maximum block weight. At current sizes, this means a maximum
/// theoretical size of:
/// * `(674 + 33 + 1) * (40_000 / 21) = 1_348_571` for a block with only outputs
/// * `(1 + 8 + 8 + 33 + 64) * (40_000 / 3) = 1_520_000` for a block with only kernels
/// * `(1 + 33) * 40_000 = 1_360_000` for a block with only inputs
///
/// Regardless of the relative numbers of inputs/outputs/kernels in a block the maximum
/// block size is around 1.5MB
/// For a block full of "average" txs (2 inputs, 2 outputs, 1 kernel) we have -
/// `(1 * 2) + (21 * 2) + (3 * 1) = 47` (weight per tx)
/// `40_000 / 47 = 851` (txs per block)
///
pub const MAX_BLOCK_WEIGHT: u64 = 40_000;
/// Fork every 6 months.
pub const HARD_FORK_INTERVAL: u64 = YEAR_HEIGHT / 2;
/// Testnet first hard fork height, set to happen around 2019-06-20
pub const TESTNET_FIRST_HARD_FORK: u64 = 185_040;
/// Testnet second hard fork height, set to happen around 2019-12-19
pub const TESTNET_SECOND_HARD_FORK: u64 = 298_080;
/// Testnet second hard fork height, set to happen around 2020-06-20
pub const TESTNET_THIRD_HARD_FORK: u64 = 552_960;
/// Testnet second hard fork height, set to happen around 2020-12-8
pub const TESTNET_FOURTH_HARD_FORK: u64 = 642_240;
/// Fork every 3 blocks
pub const TESTING_HARD_FORK_INTERVAL: u64 = 3;
/// Compute possible block version at a given height, implements
/// 6 months interval scheduled hard forks for the first 2 years.
pub fn header_version(height: u64) -> HeaderVersion {
let hf_interval = (1 + height / HARD_FORK_INTERVAL) as u16;
match global::get_chain_type() {
global::ChainTypes::Mainnet => HeaderVersion(min(5, hf_interval)),
global::ChainTypes::AutomatedTesting | global::ChainTypes::UserTesting => {
let testing_hf_interval = (1 + height / TESTING_HARD_FORK_INTERVAL) as u16;
HeaderVersion(min(5, testing_hf_interval))
}
global::ChainTypes::Testnet => {
if height < TESTNET_FIRST_HARD_FORK {
HeaderVersion(1)
} else if height < TESTNET_SECOND_HARD_FORK {
HeaderVersion(2)
} else if height < TESTNET_THIRD_HARD_FORK {
HeaderVersion(3)
} else if height < TESTNET_FOURTH_HARD_FORK {
HeaderVersion(4)
} else {
HeaderVersion(5)
}
}
}
}
/// Check whether the block version is valid at a given height, implements
/// 6 months interval scheduled hard forks for the first 2 years.
pub fn valid_header_version(height: u64, version: HeaderVersion) -> bool {
version == header_version(height)
}
/// Number of blocks used to calculate difficulty adjustment by Damped Moving Average
pub const DMA_WINDOW: u64 = HOUR_HEIGHT;
/// Difficulty adjustment half life (actually, 60s * number of 0s-blocks to raise diff by factor e) is 4 hours
pub const WTEMA_HALF_LIFE: u64 = 4 * HOUR_SEC;
/// Average time span of the DMA difficulty adjustment window
pub const BLOCK_TIME_WINDOW: u64 = DMA_WINDOW * BLOCK_TIME_SEC;
/// Clamp factor to use for DMA difficulty adjustment
/// Limit value to within this factor of goal
pub const CLAMP_FACTOR: u64 = 2;
/// Dampening factor to use for DMA difficulty adjustment
pub const DMA_DAMP_FACTOR: u64 = 3;
/// Dampening factor to use for AR scale calculation.
pub const AR_SCALE_DAMP_FACTOR: u64 = 13;
/// Compute weight of a graph as number of siphash bits defining the graph
/// The height dependence allows a 30-week linear transition from C31+ to C32+ starting after 1 year
pub fn graph_weight(height: u64, edge_bits: u8) -> u64 {
let mut xpr_edge_bits = edge_bits as u64;
let expiry_height = YEAR_HEIGHT;
if edge_bits == 31 && height >= expiry_height {
xpr_edge_bits = xpr_edge_bits.saturating_sub(1 + (height - expiry_height) / WEEK_HEIGHT);
}
// For C31 xpr_edge_bits reaches 0 at height YEAR_HEIGHT + 30 * WEEK_HEIGHT
// 30 weeks after Jan 15, 2020 would be Aug 12, 2020
(2u64 << (edge_bits - global::base_edge_bits()) as u64) * xpr_edge_bits
}
/// minimum solution difficulty after HardFork4 when PoW becomes primary only Cuckatoo32+
pub const C32_GRAPH_WEIGHT: u64 = (2u64 << (32 - BASE_EDGE_BITS) as u64) * 32; // 16384
/// Minimum difficulty, enforced in Damped Moving Average diff retargetting
/// avoids getting stuck when trying to increase difficulty subject to dampening
pub const MIN_DMA_DIFFICULTY: u64 = DMA_DAMP_FACTOR;
/// Minimum scaling factor for AR pow, enforced in diff retargetting
/// avoids getting stuck when trying to increase ar_scale subject to dampening
pub const MIN_AR_SCALE: u64 = AR_SCALE_DAMP_FACTOR;
/// unit difficulty, equal to graph_weight(SECOND_POW_EDGE_BITS)
pub const UNIT_DIFFICULTY: u64 =
((2 as u64) << (SECOND_POW_EDGE_BITS - BASE_EDGE_BITS)) * (SECOND_POW_EDGE_BITS as u64);
/// The initial difficulty at launch. This should be over-estimated
/// and difficulty should come down at launch rather than up
/// Currently grossly over-estimated at 10% of current
/// ethereum GPUs (assuming 1GPU can solve a block at diff 1 in one block interval)
pub const INITIAL_DIFFICULTY: u64 = 1_000_000 * UNIT_DIFFICULTY;
/// Minimal header information required for the Difficulty calculation to
/// take place. Used to iterate through a number of blocks. Note that an instance
/// of this is unable to calculate its own hash, due to an optimization that prevents
/// the header's PoW proof nonces from being deserialized on read
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct HeaderDifficultyInfo {
/// Hash of this block
pub hash: Option<Hash>,
/// Timestamp of the header, 1 when not used (returned info)
pub timestamp: u64,
/// Network difficulty or next difficulty to use
pub difficulty: Difficulty,
/// Network secondary PoW factor or factor to use
pub secondary_scaling: u32,
/// Whether the header is a secondary proof of work
pub is_secondary: bool,
}
impl HeaderDifficultyInfo {
/// Default constructor
pub fn new(
hash: Option<Hash>,
timestamp: u64,
difficulty: Difficulty,
secondary_scaling: u32,
is_secondary: bool,
) -> HeaderDifficultyInfo {
HeaderDifficultyInfo {
hash,
timestamp,
difficulty,
secondary_scaling,
is_secondary,
}
}
/// Constructor from a timestamp and difficulty, setting a default secondary
/// PoW factor
pub fn from_ts_diff(timestamp: u64, difficulty: Difficulty) -> HeaderDifficultyInfo {
HeaderDifficultyInfo {
hash: None,
timestamp,
difficulty,
secondary_scaling: global::initial_graph_weight(),
is_secondary: true,
}
}
/// Constructor from a difficulty and secondary factor, setting a default
/// timestamp
pub fn from_diff_scaling(
difficulty: Difficulty,
secondary_scaling: u32,
) -> HeaderDifficultyInfo {
HeaderDifficultyInfo {
hash: None,
timestamp: 1,
difficulty,
secondary_scaling,
is_secondary: true,
}
}
}
/// Move value linearly toward a goal
pub fn damp(actual: u64, goal: u64, damp_factor: u64) -> u64 {
(actual + (damp_factor - 1) * goal) / damp_factor
}
/// limit value to be within some factor from a goal
pub fn clamp(actual: u64, goal: u64, clamp_factor: u64) -> u64 {
max(goal / clamp_factor, min(actual, goal * clamp_factor))
}
/// Computes the proof-of-work difficulty that the next block should comply with.
/// Takes an iterator over past block headers information, from latest
/// (highest height) to oldest (lowest height).
/// Uses either the old dma DAA or, starting from HF4, the new wtema DAA
pub fn next_difficulty<T>(height: u64, cursor: T) -> HeaderDifficultyInfo
where
T: IntoIterator<Item = HeaderDifficultyInfo>,
{
if header_version(height) < HeaderVersion(5) {
next_dma_difficulty(height, cursor)
} else {
next_wtema_difficulty(height, cursor)
}
}
/// Difficulty calculation based on a Damped Moving Average
/// of difficulty over a window of DMA_WINDOW blocks.
/// The corresponding timespan is calculated
/// by using the difference between the timestamps at the beginning
/// and the end of the window, with a damping toward the target block time.
pub fn next_dma_difficulty<T>(height: u64, cursor: T) -> HeaderDifficultyInfo
where
T: IntoIterator<Item = HeaderDifficultyInfo>,
{
// Create vector of difficulty data running from earliest
// to latest, and pad with simulated pre-genesis data to allow earlier
// adjustment if there isn't enough window data length will be
// DMA_WINDOW + 1 (for initial block time bound)
let diff_data = global::difficulty_data_to_vector(cursor);
// First, get the ratio of secondary PoW vs primary, skipping initial header
let sec_pow_scaling = secondary_pow_scaling(height, &diff_data[1..]);
// Get the timestamp delta across the window
let ts_delta: u64 = diff_data[DMA_WINDOW as usize].timestamp - diff_data[0].timestamp;
// Get the difficulty sum of the last DMA_WINDOW elements
let diff_sum: u64 = diff_data
.iter()
.skip(1)
.map(|dd| dd.difficulty.to_num())
.sum();
// adjust time delta toward goal subject to dampening and clamping
let adj_ts = clamp(
damp(ts_delta, BLOCK_TIME_WINDOW, DMA_DAMP_FACTOR),
BLOCK_TIME_WINDOW,
CLAMP_FACTOR,
);
// minimum difficulty avoids getting stuck due to dampening
let difficulty = max(MIN_DMA_DIFFICULTY, diff_sum * BLOCK_TIME_SEC / adj_ts);
HeaderDifficultyInfo::from_diff_scaling(Difficulty::from_num(difficulty), sec_pow_scaling)
}
/// Difficulty calculation based on a Weighted Target Exponential Moving Average
/// of difficulty, using the ratio of the last block time over the target block time.
pub fn next_wtema_difficulty<T>(_height: u64, cursor: T) -> HeaderDifficultyInfo
where
T: IntoIterator<Item = HeaderDifficultyInfo>,
{
let mut last_headers = cursor.into_iter();
// last two headers
let last_header = last_headers.next().unwrap();
let prev_header = last_headers.next().unwrap();
let last_block_time: u64 = last_header.timestamp - prev_header.timestamp;
let last_diff = last_header.difficulty.to_num();
// wtema difficulty update
let next_diff =
last_diff * WTEMA_HALF_LIFE / (WTEMA_HALF_LIFE - BLOCK_TIME_SEC + last_block_time);
// mainnet minimum difficulty at graph_weight(32) ensures difficulty increase on 59s block
// since 16384 * WTEMA_HALF_LIFE / (WTEMA_HALF_LIFE - 1) > 16384
let difficulty = max(Difficulty::min_wtema(), Difficulty::from_num(next_diff));
HeaderDifficultyInfo::from_diff_scaling(difficulty, 0) // no more secondary PoW
}
/// Count, in units of 1/100 (a percent), the number of "secondary" (AR) blocks in the provided window of blocks.
pub fn ar_count(_height: u64, diff_data: &[HeaderDifficultyInfo]) -> u64 {
100 * diff_data.iter().filter(|n| n.is_secondary).count() as u64
}
/// The secondary proof-of-work factor is calculated along the same lines as in next_dma_difficulty,
/// as an adjustment on the deviation against the ideal value.
/// Factor by which the secondary proof of work difficulty will be adjusted
pub fn secondary_pow_scaling(height: u64, diff_data: &[HeaderDifficultyInfo]) -> u32 {
// Get the scaling factor sum of the last DMA_WINDOW elements
let scale_sum: u64 = diff_data.iter().map(|dd| dd.secondary_scaling as u64).sum();
// compute ideal 2nd_pow_fraction in pct and across window
let target_pct = secondary_pow_ratio(height);
let target_count = DMA_WINDOW * target_pct;
// Get the secondary count across the window, adjusting count toward goal
// subject to dampening and clamping.
let adj_count = clamp(
damp(
ar_count(height, diff_data),
target_count,
AR_SCALE_DAMP_FACTOR,
),
target_count,
CLAMP_FACTOR,
);
let scale = scale_sum * target_pct / max(1, adj_count);
// minimum AR scale avoids getting stuck due to dampening
max(MIN_AR_SCALE, scale) as u32
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_graph_weight() {
global::set_local_chain_type(global::ChainTypes::Mainnet);
// initial weights
assert_eq!(graph_weight(1, 31), 256 * 31);
assert_eq!(graph_weight(1, 32), 512 * 32);
assert_eq!(graph_weight(1, 33), 1024 * 33);
// one year in, 31 starts going down, the rest stays the same
assert_eq!(graph_weight(YEAR_HEIGHT, 31), 256 * 30);
assert_eq!(graph_weight(YEAR_HEIGHT, 32), 512 * 32);
assert_eq!(graph_weight(YEAR_HEIGHT, 33), 1024 * 33);
// 31 loses one factor per week
assert_eq!(graph_weight(YEAR_HEIGHT + WEEK_HEIGHT, 31), 256 * 29);
assert_eq!(graph_weight(YEAR_HEIGHT + 2 * WEEK_HEIGHT, 31), 256 * 28);
assert_eq!(graph_weight(YEAR_HEIGHT + 32 * WEEK_HEIGHT, 31), 0);
// 2 years in, 31 still at 0, 32 starts decreasing
assert_eq!(graph_weight(2 * YEAR_HEIGHT, 31), 0);
assert_eq!(graph_weight(2 * YEAR_HEIGHT, 32), 512 * 32);
assert_eq!(graph_weight(2 * YEAR_HEIGHT, 33), 1024 * 33);
// 32 phaseout on hold
assert_eq!(
graph_weight(2 * YEAR_HEIGHT + WEEK_HEIGHT, 32),
C32_GRAPH_WEIGHT
);
assert_eq!(graph_weight(2 * YEAR_HEIGHT + WEEK_HEIGHT, 31), 0);
assert_eq!(
graph_weight(2 * YEAR_HEIGHT + 30 * WEEK_HEIGHT, 32),
C32_GRAPH_WEIGHT
);
assert_eq!(
graph_weight(2 * YEAR_HEIGHT + 31 * WEEK_HEIGHT, 32),
C32_GRAPH_WEIGHT
);
// 3 years in, nothing changes
assert_eq!(graph_weight(3 * YEAR_HEIGHT, 31), 0);
assert_eq!(graph_weight(3 * YEAR_HEIGHT, 32), 512 * 32);
assert_eq!(graph_weight(3 * YEAR_HEIGHT, 33), 1024 * 33);
// 4 years in, still on hold
assert_eq!(graph_weight(4 * YEAR_HEIGHT, 31), 0);
assert_eq!(graph_weight(4 * YEAR_HEIGHT, 32), 512 * 32);
assert_eq!(graph_weight(4 * YEAR_HEIGHT, 33), 1024 * 33);
assert_eq!(graph_weight(4 * YEAR_HEIGHT, 33), 1024 * 33);
}
}