Remove multiply_by_rational (#11598)

* Removed multiply_by_rational
Replaced with multiply_by_rational_with_rounding

* fixes

* Test Fixes

* nightly fmt

* Test Fix

* Fixed fuzzer.

substrate/primitives/npos-elections/src/phragmen.rs

@@ -25,9 +25,9 @@ use crate::{
 	IdentifierT, PerThing128, VoteWeight, Voter,
 };
 use sp_arithmetic::{
-	helpers_128bit::multiply_by_rational,
+	helpers_128bit::multiply_by_rational_with_rounding,
 	traits::{Bounded, Zero},
-	Rational128,
+	Rational128, Rounding,
 };
 use sp_std::prelude::*;
 
@@ -143,10 +143,11 @@ pub fn seq_phragmen_core<AccountId: IdentifierT>(
 			for edge in &voter.edges {
 				let mut candidate = edge.candidate.borrow_mut();
 				if !candidate.elected && !candidate.approval_stake.is_zero() {
-					let temp_n = multiply_by_rational(
+					let temp_n = multiply_by_rational_with_rounding(
 						voter.load.n(),
 						voter.budget,
 						candidate.approval_stake,
+						Rounding::Down,
 					)
 					.unwrap_or(Bounded::max_value());
 					let temp_d = voter.load.d();
@@ -184,9 +185,14 @@ pub fn seq_phragmen_core<AccountId: IdentifierT>(
 		for edge in &mut voter.edges {
 			if edge.candidate.borrow().elected {
 				// update internal state.
-				edge.weight = multiply_by_rational(voter.budget, edge.load.n(), voter.load.n())
-					// If result cannot fit in u128. Not much we can do about it.
-					.unwrap_or(Bounded::max_value());
+				edge.weight = multiply_by_rational_with_rounding(
+					voter.budget,
+					edge.load.n(),
+					voter.load.n(),
+					Rounding::Down,
+				)
+				// If result cannot fit in u128. Not much we can do about it.
+				.unwrap_or(Bounded::max_value());
 			} else {
 				edge.weight = 0
 			}