Implement averaging_window_timespan

zebra-chain/src/parameters/network_upgrade.rs

@@ -104,6 +104,11 @@ const PRE_BLOSSOM_POW_TARGET_SPACING: i64 = 150;
 /// The target block spacing after Blossom activation.
 const POST_BLOSSOM_POW_TARGET_SPACING: i64 = 75;
 
+/// The averaging window for difficulty threshold arithmetic mean calculations.
+///
+/// `PoWAveragingWindow` in the Zcash specification.
+pub const POW_AVERAGING_WINDOW: usize = 17;
+
 /// The multiplier used to derive the testnet minimum difficulty block time gap
 /// threshold.
 ///
@@ -223,6 +228,23 @@ impl NetworkUpgrade {
             }
         }
     }
+
+    /// Returns the averaging window timespan for the network upgrade.
+    ///
+    /// `AveragingWindowTimespan` from the Zcash specification.
+    pub fn averaging_window_timespan(&self) -> Duration {
+        self.target_spacing() * POW_AVERAGING_WINDOW as _
+    }
+
+    /// Returns the averaging window timespan for `network` and `height`.
+    ///
+    /// See `averaging_window_timespan` for details.
+    pub fn averaging_window_timespan_for_height(
+        network: Network,
+        height: block::Height,
+    ) -> Duration {
+        NetworkUpgrade::current(network, height).averaging_window_timespan()
+    }
 }
 
 impl ConsensusBranchId {

zebra-state/src/service.rs

@@ -6,7 +6,7 @@ use std::{
     time::{Duration, Instant},
 };
 
-use check::difficulty::{POW_AVERAGING_WINDOW, POW_MEDIAN_BLOCK_SPAN};
+use check::difficulty::POW_MEDIAN_BLOCK_SPAN;
 use futures::future::FutureExt;
 use non_finalized_state::{NonFinalizedState, QueuedBlocks};
 use tokio::sync::oneshot;
@@ -15,6 +15,7 @@ use tracing::instrument;
 use zebra_chain::{
     block::{self, Block},
     parameters::Network,
+    parameters::POW_AVERAGING_WINDOW,
     transaction,
     transaction::Transaction,
     transparent,

zebra-state/src/service/check.rs

@@ -5,6 +5,7 @@ use std::borrow::Borrow;
 use zebra_chain::{
     block::{self, Block},
     parameters::Network,
+    parameters::POW_AVERAGING_WINDOW,
     work::difficulty::CompactDifficulty,
 };
 
@@ -13,7 +14,7 @@ use crate::{PreparedBlock, ValidateContextError};
 use super::check;
 
 pub mod difficulty;
-use difficulty::{AdjustedDifficulty, POW_AVERAGING_WINDOW, POW_MEDIAN_BLOCK_SPAN};
+use difficulty::{AdjustedDifficulty, POW_MEDIAN_BLOCK_SPAN};
 
 /// Check that `block` is contextually valid for `network`, based on the
 /// `finalized_tip_height` and `relevant_chain`.