add math methods to Fraction

src/entities/fractions/fraction.ts

@@ -41,6 +41,28 @@ export class Fraction {
     return new Fraction(this.denominator, this.numerator)
   }
 
+  add(other: Fraction | BigintIsh): Fraction {
+    const otherParsed = other instanceof Fraction ? other : new Fraction(parseBigintIsh(other))
+    return new Fraction(
+      JSBI.add(
+        JSBI.multiply(this.numerator, otherParsed.denominator),
+        JSBI.multiply(otherParsed.numerator, this.denominator)
+      ),
+      JSBI.multiply(this.denominator, otherParsed.denominator)
+    )
+  }
+
+  subtract(other: Fraction | BigintIsh): Fraction {
+    const otherParsed = other instanceof Fraction ? other : new Fraction(parseBigintIsh(other))
+    return new Fraction(
+      JSBI.subtract(
+        JSBI.multiply(this.numerator, otherParsed.denominator),
+        JSBI.multiply(otherParsed.numerator, this.denominator)
+      ),
+      JSBI.multiply(this.denominator, otherParsed.denominator)
+    )
+  }
+
   multiply(other: Fraction | BigintIsh): Fraction {
     const otherParsed = other instanceof Fraction ? other : new Fraction(parseBigintIsh(other))
     return new Fraction(
@@ -49,6 +71,14 @@ export class Fraction {
     )
   }
 
+  divide(other: Fraction | BigintIsh): Fraction {
+    const otherParsed = other instanceof Fraction ? other : new Fraction(parseBigintIsh(other))
+    return new Fraction(
+      JSBI.multiply(this.numerator, otherParsed.denominator),
+      JSBI.multiply(this.denominator, otherParsed.numerator)
+    )
+  }
+
   toSignificant(
     significantDigits: number,
     format: object = { groupSeparator: '' },

src/entities/trade.ts

 import invariant from 'tiny-invariant'
-import JSBI from 'jsbi'
 
 import { TradeType } from '../constants'
 import { Pair } from './pair'
 import { Route } from './route'
-import { Fraction, TokenAmount } from './fractions'
+import { TokenAmount } from './fractions'
 import { Price } from './fractions/price'
 import { Percent } from './fractions/percent'
 
 function getSlippage(midPrice: Price, inputAmount: TokenAmount, outputAmount: TokenAmount): Percent {
   const exactQuote = midPrice.raw.multiply(inputAmount.raw)
-  // calculate (exactQuote - outputAmount) / exactQuote
-  const exactDifference = new Fraction(
-    JSBI.subtract(exactQuote.numerator, JSBI.multiply(outputAmount.raw, exactQuote.denominator)),
-    exactQuote.denominator
-  )
-  const slippage = exactDifference.multiply(exactQuote.invert())
+  // calculate slippage := (exactQuote - outputAmount) / exactQuote
+  const slippage = exactQuote.subtract(outputAmount.raw).divide(exactQuote)
   return new Percent(slippage.numerator, slippage.denominator)
 }