Merge pull request #1369 from opentensor/fix/no-abs-in-pool-math

don't use abs directly

Author: sam0x17

pallets/subtensor/src/staking/stake_utils.rs

@@ -553,8 +553,12 @@ impl<T: Config> Pallet<T> {
         amount: u64,
     ) -> u64 {
         let mut alpha_share_pool = Self::get_alpha_share_pool(hotkey.clone(), netuid);
+        // We expect to add a positive amount here.
         let actual_alpha = alpha_share_pool.update_value_for_one(coldkey, amount as i64);
-        actual_alpha.unsigned_abs()
+
+        // We should return a positive amount, or 0 if the operation failed.
+        // e.g. the stake was removed due to precision issues.
+        actual_alpha.max(0).unsigned_abs()
     }
 
     pub fn try_increase_stake_for_hotkey_and_coldkey_on_subnet(
@@ -583,14 +587,20 @@ impl<T: Config> Pallet<T> {
         amount: u64,
     ) -> u64 {
         let mut alpha_share_pool = Self::get_alpha_share_pool(hotkey.clone(), netuid);
+
+        // We expect a negative value here
         let mut actual_alpha = 0;
         if let Ok(value) = alpha_share_pool.try_get_value(coldkey) {
             if value >= amount {
                 actual_alpha =
                     alpha_share_pool.update_value_for_one(coldkey, (amount as i64).neg());
             }
         }
-        actual_alpha.unsigned_abs()
+
+        // Get the negation of the removed alpha, and clamp at 0.
+        // This ensures we return a positive value, but only if
+        // `actual_alpha` was negative (i.e. a decrease in stake).
+        actual_alpha.neg().max(0).unsigned_abs()
     }
 
     /// Calculates Some(Alpha) returned from pool by staking operation