Move state trans fns into state_processing

eth2/state_processing/src/per_epoch_processing/process_slashings.rs

@@ -0,0 +1,36 @@
+use types::{BeaconStateError as Error, *};
+
+/// Process slashings.
+///
+/// Note: Utilizes the cache and will fail if the appropriate cache is not initialized.
+///
+/// Spec v0.4.0
+pub fn process_slashings(state: &mut BeaconState, spec: &ChainSpec) -> Result<(), Error> {
+    let current_epoch = state.current_epoch(spec);
+    let active_validator_indices = state.get_active_validator_indices(current_epoch, spec)?;
+    let total_balance = state.get_total_balance(&active_validator_indices[..], spec)?;
+
+    for (index, validator) in state.validator_registry.iter().enumerate() {
+        if validator.slashed
+            && (current_epoch
+                == validator.withdrawable_epoch - Epoch::from(spec.latest_slashed_exit_length / 2))
+        {
+            // TODO: check the following two lines are correct.
+            let total_at_start = state.get_slashed_balance(current_epoch + 1, spec)?;
+            let total_at_end = state.get_slashed_balance(current_epoch, spec)?;
+
+            let total_penalities = total_at_end.saturating_sub(total_at_start);
+
+            let effective_balance = state.get_effective_balance(index, spec)?;
+            let penalty = std::cmp::max(
+                effective_balance * std::cmp::min(total_penalities * 3, total_balance)
+                    / total_balance,
+                effective_balance / spec.min_penalty_quotient,
+            );
+
+            safe_sub_assign!(state.validator_balances[index], penalty);
+        }
+    }
+
+    Ok(())
+}