Directory Restructure (#1163)

* Move tests -> testing

* Directory restructure

* Update Cargo.toml during restructure

* Update Makefile during restructure

* Fix arbitrary path

consensus/state_processing/src/common/mod.rs

@@ -0,0 +1,34 @@
+mod deposit_data_tree;
+mod get_attesting_indices;
+mod get_base_reward;
+mod get_indexed_attestation;
+mod initiate_validator_exit;
+mod slash_validator;
+
+pub use deposit_data_tree::DepositDataTree;
+pub use get_attesting_indices::get_attesting_indices;
+pub use get_base_reward::get_base_reward;
+pub use get_indexed_attestation::get_indexed_attestation;
+pub use initiate_validator_exit::initiate_validator_exit;
+pub use slash_validator::slash_validator;
+
+use safe_arith::{ArithError, SafeArith};
+use types::{BeaconState, EthSpec};
+
+/// Increase the balance of a validator, erroring upon overflow, as per the spec.
+///
+/// Spec v0.11.2
+pub fn increase_balance<E: EthSpec>(
+    state: &mut BeaconState<E>,
+    index: usize,
+    delta: u64,
+) -> Result<(), ArithError> {
+    state.balances[index].safe_add_assign(delta)
+}
+
+/// Decrease the balance of a validator, saturating upon overflow, as per the spec.
+///
+/// Spec v0.11.2
+pub fn decrease_balance<E: EthSpec>(state: &mut BeaconState<E>, index: usize, delta: u64) {
+    state.balances[index] = state.balances[index].saturating_sub(delta);
+}