fix lstrip in biguint (#6151)

* add failing test for multiply_by_rational

* fix BigUint

* fix length

* bump version

* merge tests

substrate/bin/node/runtime/src/lib.rs

@@ -94,7 +94,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	// implementation changes and behavior does not, then leave spec_version as
 	// is and increment impl_version.
 	spec_version: 251,
-	impl_version: 0,
+	impl_version: 1,
 	apis: RUNTIME_API_VERSIONS,
 	transaction_version: 1,
 };

substrate/primitives/arithmetic/src/biguint.rs

@@ -151,7 +151,7 @@ impl BigUint {
 		// has the ability to cause this. There is nothing to do if the number already has 1
 		// limb only. call it a day and return.
 		if self.len().is_zero() { return; }
-		let index = self.digits.iter().position(|&elem| elem != 0).unwrap_or(0);
+		let index = self.digits.iter().position(|&elem| elem != 0).unwrap_or(self.len() - 1);
 
 		if index > 0 {
 			self.digits = self.digits[index..].to_vec()
@@ -581,19 +581,19 @@ pub mod tests {
 	fn strip_works() {
 		let mut a = BigUint::from_limbs(&[0, 1, 0]);
 		a.lstrip();
-		assert_eq!(a, BigUint { digits: vec![1, 0] });
+		assert_eq!(a.digits, vec![1, 0]);
 
 		let mut a = BigUint::from_limbs(&[0, 0, 1]);
 		a.lstrip();
-		assert_eq!(a, BigUint { digits: vec![1] });
+		assert_eq!(a.digits, vec![1]);
 
 		let mut a = BigUint::from_limbs(&[0, 0]);
 		a.lstrip();
-		assert_eq!(a, BigUint { digits: vec![0] });
+		assert_eq!(a.digits, vec![0]);
 
 		let mut a = BigUint::from_limbs(&[0, 0, 0]);
 		a.lstrip();
-		assert_eq!(a, BigUint { digits: vec![0] });
+		assert_eq!(a.digits, vec![0]);
 	}
 
 	#[test]

substrate/primitives/arithmetic/src/rational128.rs

@@ -360,6 +360,15 @@ mod tests {
 			multiply_by_rational(1_000_000_000, MAX128 / 8, MAX128 / 2).unwrap(),
 			250000000,
 		);
+
+		assert_eq!(
+			multiply_by_rational(
+				29459999999999999988000u128,
+				1000000000000000000u128,
+				10000000000000000000u128
+			).unwrap(),
+			2945999999999999998800u128
+		);
 	}
 
 	#[test]