Add the pre-electra slashing processing

consensus/state_processing/src/per_epoch_processing/single_pass.rs

@@ -80,6 +80,7 @@ struct RewardsAndPenaltiesContext {
 }
 
 struct SlashingsContext {
+    adjusted_total_slashing_balance: u64,
     target_withdrawable_epoch: Epoch,
     penalty_per_effective_balance_increment: u64,
 }
@@ -299,7 +300,7 @@ pub fn process_epoch_single_pass<E: EthSpec>(
 
         // `process_slashings`
         if conf.slashings {
-            process_single_slashing(&mut balance, &validator, slashings_ctxt, spec)?;
+            process_single_slashing(&mut balance, &validator, slashings_ctxt, state_ctxt, spec)?;
         }
 
         // `process_pending_balance_deposits`
@@ -782,6 +783,7 @@ impl SlashingsContext {
         )?;
 
         Ok(Self {
+            adjusted_total_slashing_balance,
             target_withdrawable_epoch,
             penalty_per_effective_balance_increment,
         })
@@ -792,16 +794,28 @@ fn process_single_slashing(
     balance: &mut Cow<u64>,
     validator: &Validator,
     slashings_ctxt: &SlashingsContext,
+    state_ctxt: &StateContext,
     spec: &ChainSpec,
 ) -> Result<(), Error> {
     if validator.slashed && slashings_ctxt.target_withdrawable_epoch == validator.withdrawable_epoch
     {
         let increment = spec.effective_balance_increment;
-        let effective_balance_increments = validator.effective_balance.safe_div(increment)?;
-        let penalty = slashings_ctxt
-            .penalty_per_effective_balance_increment
-            .safe_mul(effective_balance_increments)?;
-
+        let penalty = if state_ctxt.fork_name.electra_enabled() {
+            let effective_balance_increments = validator.effective_balance.safe_div(increment)?;
+            let penalty = slashings_ctxt
+                .penalty_per_effective_balance_increment
+                .safe_mul(effective_balance_increments)?;
+            penalty
+        } else {
+            let penalty_numerator = validator
+                .effective_balance
+                .safe_div(increment)?
+                .safe_mul(slashings_ctxt.adjusted_total_slashing_balance)?;
+            let penalty = penalty_numerator
+                .safe_div(state_ctxt.total_active_balance)?
+                .safe_mul(increment)?;
+            penalty
+        };
         *balance.make_mut()? = balance.saturating_sub(penalty);
     }
     Ok(())