Fix PerThing::from_percent.

primitives/arithmetic/src/lib.rs

@@ -515,3 +515,17 @@ mod threshold_compare_tests {
 		assert_eq!(Saturating::saturating_pow(i32::max_value(), 2), i32::max_value());
 	}
 }
+
+#[cfg(test)]
+mod per_thing {
+	use super::*;
+
+	#[test]
+	fn per_thing_100_wont_overflow() {
+		<Percent as PerThing>::from_percent(100);
+		<PerU16 as PerThing>::from_percent(100);
+		<Permill as PerThing>::from_percent(100);
+		<Perbill as PerThing>::from_percent(100);
+		<Perquintill as PerThing>::from_percent(100);
+	}
+}

primitives/arithmetic/src/per_things.rs

@@ -67,7 +67,8 @@ pub trait PerThing:
 		let b = Self::ACCURACY;
 		// if Self::ACCURACY % 100 > 0 then we need the correction for accuracy
 		let c = rational_mul_correction::<Self::Inner, Self>(b, a, 100.into(), Rounding::Nearest);
-		Self::from_parts(a / 100.into() * b + c)
+		let base: Self::Inner = 100.into();
+		Self::from_parts(a / base.saturating_mul(b).saturating_add(c))
 	}
 
 	/// Return the product of multiplication of this value by itself.
@@ -334,7 +335,7 @@ macro_rules! implement_per_thing {
 				&self.0
 			}
 			fn decode_from(x: Self::As) -> Self {
-				// Saturates if `x` is more than `$max` internally. 
+				// Saturates if `x` is more than `$max` internally.
 				Self::from_parts(x)
 			}
 		}