database: split cumulative_difficulty into low/high bits (#114)

* types: split `cumulative_difficulty` into low/high bits

* helper: add `map` module

* database: use `helper`'s cumulative_diff functions

* helper: rename functions

splitting bits isn't necessarily `cumulative_difficulty` specific

* database: fix tests

* helper: docs

* helper: test output is low-endian bits

* helper: docs

* Update helper/src/map.rs

Co-authored-by: Boog900 <boog900@tutanota.com>

* Update helper/src/map.rs

Co-authored-by: Boog900 <boog900@tutanota.com>

---------

Co-authored-by: Boog900 <boog900@tutanota.com>

database/Cargo.toml

@@ -25,7 +25,7 @@ cfg-if   = { workspace = true }
 # FIXME:
 # We only need the `thread` feature if `service` is enabled.
 # Figure out how to enable features of an already pulled in dependency conditionally.
-cuprate-helper   = { path = "../helper", features = ["fs", "thread"] }
+cuprate-helper   = { path = "../helper", features = ["fs", "thread", "map"] }
 cuprate-types    = { path = "../types", features = ["service"] }
 curve25519-dalek = { workspace = true }
 monero-pruning   = { path = "../pruning" }

database/src/backend/tests.rs

@@ -434,7 +434,8 @@ test_tables! {
         timestamp: 1,
         cumulative_generated_coins: 123,
         weight: 321,
-        cumulative_difficulty: 111,
+        cumulative_difficulty_low: 111,
+        cumulative_difficulty_high: 111,
         block_hash: [54; 32],
         cumulative_rct_outs: 2389,
         long_term_weight: 2389,

database/src/ops/block.rs

@@ -10,6 +10,7 @@ use monero_serai::{
     transaction::{Input, Timelock, Transaction},
 };
 
+use cuprate_helper::map::{combine_low_high_bits_to_u128, split_u128_into_low_high_bits};
 use cuprate_types::{ExtendedBlockHeader, TransactionVerificationData, VerifiedBlockInformation};
 
 use crate::{
@@ -102,14 +103,18 @@ pub fn add_block(
         cumulative_generated_coins(&block.height.saturating_sub(1), tables.block_infos())?
             + block.generated_coins;
 
+    let (cumulative_difficulty_low, cumulative_difficulty_high) =
+        split_u128_into_low_high_bits(block.cumulative_difficulty);
+
     // Block Info.
     tables.block_infos_mut().put(
         &block.height,
         &BlockInfo {
+            cumulative_difficulty_low,
+            cumulative_difficulty_high,
             cumulative_generated_coins,
             cumulative_rct_outs,
             timestamp: block.block.header.timestamp,
-            cumulative_difficulty: block.cumulative_difficulty,
             block_hash: block.block_hash,
             // INVARIANT: #[cfg] @ lib.rs asserts `usize == u64`
             weight: block.weight as u64,
@@ -192,13 +197,18 @@ pub fn get_block_extended_header_from_height(
     let block_blob = tables.block_blobs().get(block_height)?.0;
     let block = Block::read(&mut block_blob.as_slice())?;
 
+    let cumulative_difficulty = combine_low_high_bits_to_u128(
+        block_info.cumulative_difficulty_low,
+        block_info.cumulative_difficulty_high,
+    );
+
     // INVARIANT: #[cfg] @ lib.rs asserts `usize == u64`
     #[allow(clippy::cast_possible_truncation)]
     Ok(ExtendedBlockHeader {
+        cumulative_difficulty,
         version: block.header.major_version,
         vote: block.header.minor_version,
         timestamp: block.header.timestamp,
-        cumulative_difficulty: block_info.cumulative_difficulty,
         block_weight: block_info.weight as usize,
         long_term_weight: block_info.long_term_weight as usize,
     })

database/src/types.rs

@@ -138,7 +138,8 @@ pub struct PreRctOutputId {
 ///     timestamp: 1,
 ///     cumulative_generated_coins: 123,
 ///     weight: 321,
-///     cumulative_difficulty: 112,
+///     cumulative_difficulty_low: 112,
+///     cumulative_difficulty_high: 112,
 ///     block_hash: [54; 32],
 ///     cumulative_rct_outs: 2389,
 ///     long_term_weight: 2389,
@@ -165,8 +166,10 @@ pub struct BlockInfo {
     pub cumulative_generated_coins: u64,
     /// TODO
     pub weight: u64,
-    /// TODO
-    pub cumulative_difficulty: u128,
+    /// Least-significant 64 bits of the 128-bit cumulative difficulty.
+    pub cumulative_difficulty_low: u64,
+    /// Most-significant 64 bits of the 128-bit cumulative difficulty.
+    pub cumulative_difficulty_high: u64,
     /// TODO
     pub block_hash: [u8; 32],
     /// TODO

helper/Cargo.toml

@@ -10,13 +10,14 @@ repository = "https://github.com/Cuprate/cuprate/tree/main/consensus"
 
 [features]
 # All features on by default.
-default   = ["std", "atomic", "asynch", "fs", "num", "time", "thread", "constants"]
+default   = ["std", "atomic", "asynch", "fs", "num", "map", "time", "thread", "constants"]
 std       = []
 atomic    = ["dep:crossbeam"]
 asynch    = ["dep:futures", "dep:rayon"]
 constants = []
 fs        = ["dep:dirs"]
 num       = []
+map       = []
 time      = ["dep:chrono", "std"]
 thread    = ["std", "dep:target_os_lib"]
 

helper/src/lib.rs

@@ -51,6 +51,9 @@ pub mod network;
 #[cfg(feature = "num")]
 pub mod num;
 
+#[cfg(feature = "map")]
+pub mod map;
+
 #[cfg(feature = "thread")]
 pub mod thread;
 

helper/src/map.rs

@@ -0,0 +1,58 @@
+//! Mapping of data types.
+//!
+//! This module provides functions solely for mapping data types into others, mostly similar ones.
+//!
+//! `#[no_std]` compatible.
+
+//---------------------------------------------------------------------------------------------------- Use
+
+//---------------------------------------------------------------------------------------------------- `(u64, u64) <-> u128`
+/// Split a [`u128`] value into 2 64-bit values.
+///
+/// The tuple returned is `(low, high)` where `low` is the least significant
+/// 64-bits of `number`, and `high` is the most significant.
+///
+/// Note that the output of this function are `u64` representations of _bits_, not numerical values.
+///
+/// See [`combine_low_high_bits_to_u128`] for the inverse function.
+///
+/// ```rust
+/// # use cuprate_helper::map::*;
+/// let value = u128::MAX - 1;
+/// let low = u64::MAX - 1;
+/// let high = u64::MAX;
+///
+/// assert_eq!(split_u128_into_low_high_bits(value), (low, high));
+/// ```
+#[inline]
+pub const fn split_u128_into_low_high_bits(value: u128) -> (u64, u64) {
+    (value as u64, (value >> 64) as u64)
+}
+
+/// Combine 2 64-bit values into a single [`u128`] value.
+///
+/// The inputs:
+/// - `low_bits` are the _least_ significant 64-bits of `cumulative_difficulty`
+/// - `high_bits` are the _most_ significant 64-bits of `cumulative_difficulty`
+///
+/// Note that `low_bits` & `high_bits` should be `u64` representation of _bits_, not numerical values.
+///
+/// See [`split_u128_into_low_high_bits`] for the inverse function.
+///
+/// ```rust
+/// # use cuprate_helper::map::*;
+/// let value = u128::MAX - 1;
+/// let low = u64::MAX - 1;
+/// let high = u64::MAX;
+///
+/// assert_eq!(combine_low_high_bits_to_u128(low, high), value);
+/// ```
+#[inline]
+pub const fn combine_low_high_bits_to_u128(low_bits: u64, high_bits: u64) -> u128 {
+    let res = (high_bits as u128) << 64;
+    res | (low_bits as u128)
+}
+
+//---------------------------------------------------------------------------------------------------- Tests
+#[cfg(test)]
+mod test {}