CU-1yykjpw Fix calc_utilization_ratio() and add proptest for it.

frame/composable-traits/src/lending/math.rs

@@ -39,15 +39,11 @@ pub fn calc_utilization_ratio(
 	}
 
 	let total = cash.safe_add(&borrows)?;
-	// also max value is 1.00000000000000000, it still fails with u8, so mul by u16 and cast to u8
-	// safely
 	let utilization_ratio = borrows
 		.checked_div(&total)
 		.expect("above checks prove it cannot error")
-		.checked_mul_int(100_u16)
-		.ok_or(ArithmeticError::Overflow)?
-		.try_into()
-		.map_err(|_| ArithmeticError::Overflow)?;
+		.checked_mul_int(100_u8)
+		.ok_or(ArithmeticError::Overflow)?;
 	Ok(Percent::from_percent(utilization_ratio))
 }
 

frame/composable-traits/src/rate_model.rs

@@ -47,28 +47,6 @@ pub type Ratio = FixedU128;
 /// accounts to length of year)
 pub const SECONDS_PER_YEAR: DurationSeconds = 365 * 24 * ONE_HOUR;
 
-/// utilization_ratio = total_borrows / (total_cash + total_borrows)
-pub fn calc_utilization_ratio(
-	cash: LiftedFixedBalance,
-	borrows: LiftedFixedBalance,
-) -> Result<Percent, ArithmeticError> {
-	if borrows.is_zero() {
-		return Ok(Percent::zero())
-	}
-
-	let total = cash.safe_add(&borrows)?;
-	// also max value is 1.00000000000000000, it still fails with u8, so mul by u16 and cast to u8
-	// safely
-	let utilization_ratio = borrows
-		.checked_div(&total)
-		.expect("above checks prove it cannot error")
-		.checked_mul_int(100_u16)
-		.ok_or(ArithmeticError::Overflow)?
-		.try_into()
-		.map_err(|_| ArithmeticError::Overflow)?;
-	Ok(Percent::from_percent(utilization_ratio))
-}
-
 pub trait InterestRate {
 	fn get_borrow_rate(&mut self, utilization: Percent) -> Option<Rate>;
 }

frame/lending/src/tests.rs

@@ -331,6 +331,7 @@ fn new_jump_model() -> (Percent, InterestRateModel) {
 fn test_calc_utilization_ratio() {
 	// 50% borrow
 	assert_eq!(Lending::calc_utilization_ratio(&1, &1).unwrap(), Percent::from_percent(50));
+	assert_eq!(Lending::calc_utilization_ratio(&1, &1).unwrap(), Percent::from_float(0.50));
 	assert_eq!(Lending::calc_utilization_ratio(&100, &100).unwrap(), Percent::from_percent(50));
 	// no borrow
 	assert_eq!(Lending::calc_utilization_ratio(&1, &0).unwrap(), Percent::zero());
@@ -705,6 +706,13 @@ prop_compose! {
 	}
 }
 
+prop_compose! {
+	fn valid_cash_borrow()(cash in 1..u32::MAX)(borrow in 0..cash, cash in Just(cash))
+		-> (u32, u32) {
+			(cash, borrow)
+	}
+}
+
 prop_compose! {
 	fn valid_amounts_without_overflow_2()
 		(x in MINIMUM_BALANCE..u64::MAX as Balance / 2,
@@ -831,6 +839,14 @@ proptest! {
 		})?;
 	}
 
+	#[test]
+	fn calc_utilization_ratio_proptest((cash, borrow) in valid_cash_borrow()) {
+		new_test_ext().execute_with(|| {
+			prop_assert_eq!(Lending::calc_utilization_ratio(&cash.into(), &borrow.into()).unwrap(), Percent::from_float(borrow as f64 / (cash as f64 + borrow as f64)));
+			Ok(())
+		})?;
+	}
+
 	#[test]
 	fn market_creation_with_multi_level_priceable_lp(depth in 0..20) {
 		new_test_ext().execute_with(|| {