Add trait for saturating arithmetic (#15812)

* Add SaturatingArithmetic trait

* Use Duration saturating arithmetic

* Use new macro to fix poh_config

sdk/src/arithmetic.rs

@@ -0,0 +1,45 @@
+use std::time::Duration;
+
+/// A helper trait for primitive types that do not yet implement saturating arithmetic methods
+pub trait SaturatingArithmetic<T> {
+    fn sol_saturating_add(&self, rhs: Self) -> Self;
+    fn sol_saturating_sub(&self, rhs: Self) -> Self;
+    fn sol_saturating_mul(&self, rhs: T) -> Self;
+}
+
+/// Saturating arithmetic for Duration, until Rust support moves from nightly to stable
+/// Duration::MAX is constructed manually, as Duration consts are not yet stable either.
+impl SaturatingArithmetic<u32> for Duration {
+    fn sol_saturating_add(&self, rhs: Self) -> Self {
+        self.checked_add(rhs)
+            .unwrap_or_else(|| Self::new(u64::MAX, 1_000_000_000u32.saturating_sub(1)))
+    }
+    fn sol_saturating_sub(&self, rhs: Self) -> Self {
+        self.checked_sub(rhs).unwrap_or_else(|| Self::new(0, 0))
+    }
+    fn sol_saturating_mul(&self, rhs: u32) -> Self {
+        self.checked_mul(rhs)
+            .unwrap_or_else(|| Self::new(u64::MAX, 1_000_000_000u32.saturating_sub(1)))
+    }
+}
+
+#[cfg(test)]
+pub mod tests {
+    use super::*;
+
+    #[test]
+    fn test_duration() {
+        let empty_duration = Duration::new(0, 0);
+        let max_duration = Duration::new(u64::MAX, 1_000_000_000 - 1);
+        let duration = Duration::new(u64::MAX, 0);
+
+        let add = duration.sol_saturating_add(duration);
+        assert_eq!(add, max_duration);
+
+        let sub = duration.sol_saturating_sub(max_duration);
+        assert_eq!(sub, empty_duration);
+
+        let mult = duration.sol_saturating_mul(u32::MAX);
+        assert_eq!(mult, max_duration);
+    }
+}

sdk/src/lib.rs

@@ -8,6 +8,7 @@ pub use solana_program::*;
 
 pub mod account;
 pub mod account_utils;
+pub mod arithmetic;
 pub mod builtins;
 pub mod client;
 pub mod commitment_config;

sdk/src/poh_config.rs

@@ -1,5 +1,4 @@
-#![allow(clippy::integer_arithmetic)]
-use crate::clock::DEFAULT_TICKS_PER_SECOND;
+use crate::{clock::DEFAULT_TICKS_PER_SECOND, unchecked_div_by_const};
 use std::time::Duration;
 
 #[derive(Serialize, Deserialize, Clone, Debug, AbiExample)]
@@ -29,8 +28,9 @@ impl PohConfig {
 
 impl Default for PohConfig {
     fn default() -> Self {
-        Self::new_sleep(Duration::from_micros(
-            1000 * 1000 / DEFAULT_TICKS_PER_SECOND,
-        ))
+        Self::new_sleep(Duration::from_micros(unchecked_div_by_const!(
+            1000 * 1000,
+            DEFAULT_TICKS_PER_SECOND
+        )))
     }
 }

sdk/src/stake_weighted_timestamp.rs

@@ -1,6 +1,7 @@
 /// A helper for calculating a stake-weighted timestamp estimate from a set of timestamps and epoch
 /// stake.
 use solana_sdk::{
+    arithmetic::SaturatingArithmetic,
     clock::{Slot, UnixTimestamp},
     pubkey::Pubkey,
 };
@@ -43,7 +44,7 @@ where
     let mut total_stake: u128 = 0;
     for (vote_pubkey, slot_timestamp) in unique_timestamps {
         let (timestamp_slot, timestamp) = slot_timestamp.borrow();
-        let offset = slot.saturating_sub(*timestamp_slot) as u32 * slot_duration;
+        let offset = slot_duration.sol_saturating_mul(slot.saturating_sub(*timestamp_slot) as u32);
         let estimate = timestamp.saturating_add(offset.as_secs() as i64);
         let stake = stakes
             .get(vote_pubkey.borrow())
@@ -70,16 +71,19 @@ where
     }
     // Bound estimate by `max_allowable_drift` since the start of the epoch
     if let Some((epoch_start_slot, epoch_start_timestamp)) = epoch_start_timestamp {
-        let poh_estimate_offset = slot.saturating_sub(epoch_start_slot) as u32 * slot_duration;
+        let poh_estimate_offset =
+            slot_duration.sol_saturating_mul(slot.saturating_sub(epoch_start_slot) as u32);
         let estimate_offset = Duration::from_secs(if fix_estimate_into_u64 {
             (estimate as u64).saturating_sub(epoch_start_timestamp as u64)
         } else {
             estimate.saturating_sub(epoch_start_timestamp) as u64
         });
-        let max_allowable_drift_fast = poh_estimate_offset * max_allowable_drift.fast / 100;
-        let max_allowable_drift_slow = poh_estimate_offset * max_allowable_drift.slow / 100;
+        let max_allowable_drift_fast =
+            poh_estimate_offset.sol_saturating_mul(max_allowable_drift.fast) / 100;
+        let max_allowable_drift_slow =
+            poh_estimate_offset.sol_saturating_mul(max_allowable_drift.slow) / 100;
         if estimate_offset > poh_estimate_offset
-            && estimate_offset - poh_estimate_offset > max_allowable_drift_slow
+            && estimate_offset.sol_saturating_sub(poh_estimate_offset) > max_allowable_drift_slow
         {
             // estimate offset since the start of the epoch is higher than
             // `MAX_ALLOWABLE_DRIFT_PERCENTAGE_SLOW`
@@ -87,7 +91,7 @@ where
                 .saturating_add(poh_estimate_offset.as_secs() as i64)
                 .saturating_add(max_allowable_drift_slow.as_secs() as i64);
         } else if estimate_offset < poh_estimate_offset
-            && poh_estimate_offset - estimate_offset > max_allowable_drift_fast
+            && poh_estimate_offset.sol_saturating_sub(estimate_offset) > max_allowable_drift_fast
         {
             // estimate offset since the start of the epoch is lower than
             // `MAX_ALLOWABLE_DRIFT_PERCENTAGE_FAST`