math: Change Decimal.multiply to operate on Uint classes

cosmos · Aug 19, 2020 · a737df0 · a737df0
1 parent 3af1098
commit a737df0
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Showing 4 changed files with 74 additions and 33 deletions.
diff --git a/packages/launchpad/src/gas.ts b/packages/launchpad/src/gas.ts
@@ -1,4 +1,4 @@
-import { Decimal } from "@cosmjs/math";
+import { Decimal, Uint53 } from "@cosmjs/math";
 
 import { coins } from "./coins";
 import { StdFee } from "./types";
@@ -34,8 +34,7 @@ export type GasLimits<T extends Record<string, StdFee>> = {
 };
 
 function calculateFee(gasLimit: number, { denom, amount: gasPriceAmount }: GasPrice): StdFee {
-  const gasLimitDecimal = Decimal.fromUserInput(gasLimit.toString(), gasPriceAmount.fractionalDigits);
-  const amount = Math.ceil(gasPriceAmount.multiply(gasLimitDecimal).toFloatApproximation());
+  const amount = Math.ceil(gasPriceAmount.multiply(new Uint53(gasLimit)).toFloatApproximation());
   return {
     amount: coins(amount, denom),
     gas: gasLimit.toString(),

diff --git a/packages/math/src/decimal.spec.ts b/packages/math/src/decimal.spec.ts
@@ -1,4 +1,5 @@
 import { Decimal } from "./decimal";
+import { Uint32, Uint53, Uint64 } from "./integers";
 
 describe("Decimal", () => {
   describe("fromAtomics", () => {
@@ -212,43 +213,83 @@ describe("Decimal", () => {
   });
 
   describe("multiply", () => {
-    it("returns correct values", () => {
+    it("returns correct values for Uint32", () => {
       const zero = Decimal.fromUserInput("0", 5);
-      expect(zero.multiply(Decimal.fromUserInput("0", 5)).toString()).toEqual("0");
-      expect(zero.multiply(Decimal.fromUserInput("1", 5)).toString()).toEqual("0");
-      expect(zero.multiply(Decimal.fromUserInput("2", 5)).toString()).toEqual("0");
-      expect(zero.multiply(Decimal.fromUserInput("2.8", 5)).toString()).toEqual("0");
-      expect(zero.multiply(Decimal.fromUserInput("0.12345", 5)).toString()).toEqual("0");
+      expect(zero.multiply(new Uint32(0)).toString()).toEqual("0");
+      expect(zero.multiply(new Uint32(1)).toString()).toEqual("0");
+      expect(zero.multiply(new Uint32(2)).toString()).toEqual("0");
+      expect(zero.multiply(new Uint32(4294967295)).toString()).toEqual("0");
 
       const one = Decimal.fromUserInput("1", 5);
-      expect(one.multiply(Decimal.fromUserInput("0", 5)).toString()).toEqual("0");
-      expect(one.multiply(Decimal.fromUserInput("1", 5)).toString()).toEqual("1");
-      expect(one.multiply(Decimal.fromUserInput("2", 5)).toString()).toEqual("2");
-      expect(one.multiply(Decimal.fromUserInput("2.8", 5)).toString()).toEqual("2.8");
-      expect(one.multiply(Decimal.fromUserInput("0.12345", 5)).toString()).toEqual("0.12345");
+      expect(one.multiply(new Uint32(0)).toString()).toEqual("0");
+      expect(one.multiply(new Uint32(1)).toString()).toEqual("1");
+      expect(one.multiply(new Uint32(2)).toString()).toEqual("2");
+      expect(one.multiply(new Uint32(4294967295)).toString()).toEqual("4294967295");
 
       const oneDotFive = Decimal.fromUserInput("1.5", 5);
-      expect(oneDotFive.multiply(Decimal.fromUserInput("0", 5)).toString()).toEqual("0");
-      expect(oneDotFive.multiply(Decimal.fromUserInput("1", 5)).toString()).toEqual("1.5");
-      expect(oneDotFive.multiply(Decimal.fromUserInput("2", 5)).toString()).toEqual("3");
-      expect(oneDotFive.multiply(Decimal.fromUserInput("2.8", 5)).toString()).toEqual("4.2");
-      expect(oneDotFive.multiply(Decimal.fromUserInput("0.12345", 5)).toString()).toEqual("0.18517");
+      expect(oneDotFive.multiply(new Uint32(0)).toString()).toEqual("0");
+      expect(oneDotFive.multiply(new Uint32(1)).toString()).toEqual("1.5");
+      expect(oneDotFive.multiply(new Uint32(2)).toString()).toEqual("3");
+      expect(oneDotFive.multiply(new Uint32(4294967295)).toString()).toEqual("6442450942.5");
 
       // original value remain unchanged
       expect(zero.toString()).toEqual("0");
       expect(one.toString()).toEqual("1");
       expect(oneDotFive.toString()).toEqual("1.5");
     });
 
-    it("throws for different fractional digits", () => {
+    it("returns correct values for Uint53", () => {
+      const zero = Decimal.fromUserInput("0", 5);
+      expect(zero.multiply(new Uint53(0)).toString()).toEqual("0");
+      expect(zero.multiply(new Uint53(1)).toString()).toEqual("0");
+      expect(zero.multiply(new Uint53(2)).toString()).toEqual("0");
+      expect(zero.multiply(new Uint53(9007199254740991)).toString()).toEqual("0");
+
+      const one = Decimal.fromUserInput("1", 5);
+      expect(one.multiply(new Uint53(0)).toString()).toEqual("0");
+      expect(one.multiply(new Uint53(1)).toString()).toEqual("1");
+      expect(one.multiply(new Uint53(2)).toString()).toEqual("2");
+      expect(one.multiply(new Uint53(9007199254740991)).toString()).toEqual("9007199254740991");
+
+      const oneDotFive = Decimal.fromUserInput("1.5", 5);
+      expect(oneDotFive.multiply(new Uint53(0)).toString()).toEqual("0");
+      expect(oneDotFive.multiply(new Uint53(1)).toString()).toEqual("1.5");
+      expect(oneDotFive.multiply(new Uint53(2)).toString()).toEqual("3");
+      expect(oneDotFive.multiply(new Uint53(9007199254740991)).toString()).toEqual("13510798882111486.5");
+
+      // original value remain unchanged
+      expect(zero.toString()).toEqual("0");
+      expect(one.toString()).toEqual("1");
+      expect(oneDotFive.toString()).toEqual("1.5");
+    });
+
+    it("returns correct values for Uint64", () => {
       const zero = Decimal.fromUserInput("0", 5);
-      expect(() => zero.multiply(Decimal.fromUserInput("1", 1))).toThrowError(/do not match/i);
-      expect(() => zero.multiply(Decimal.fromUserInput("1", 2))).toThrowError(/do not match/i);
-      expect(() => zero.multiply(Decimal.fromUserInput("1", 3))).toThrowError(/do not match/i);
-      expect(() => zero.multiply(Decimal.fromUserInput("1", 4))).toThrowError(/do not match/i);
+      expect(zero.multiply(Uint64.fromString("0")).toString()).toEqual("0");
+      expect(zero.multiply(Uint64.fromString("1")).toString()).toEqual("0");
+      expect(zero.multiply(Uint64.fromString("2")).toString()).toEqual("0");
+      expect(zero.multiply(Uint64.fromString("18446744073709551615")).toString()).toEqual("0");
+
+      const one = Decimal.fromUserInput("1", 5);
+      expect(one.multiply(Uint64.fromString("0")).toString()).toEqual("0");
+      expect(one.multiply(Uint64.fromString("1")).toString()).toEqual("1");
+      expect(one.multiply(Uint64.fromString("2")).toString()).toEqual("2");
+      expect(one.multiply(Uint64.fromString("18446744073709551615")).toString()).toEqual(
+        "18446744073709551615",
+      );
+
+      const oneDotFive = Decimal.fromUserInput("1.5", 5);
+      expect(oneDotFive.multiply(Uint64.fromString("0")).toString()).toEqual("0");
+      expect(oneDotFive.multiply(Uint64.fromString("1")).toString()).toEqual("1.5");
+      expect(oneDotFive.multiply(Uint64.fromString("2")).toString()).toEqual("3");
+      expect(oneDotFive.multiply(Uint64.fromString("18446744073709551615")).toString()).toEqual(
+        "27670116110564327422.5",
+      );
 
-      expect(() => zero.multiply(Decimal.fromUserInput("1", 6))).toThrowError(/do not match/i);
-      expect(() => zero.multiply(Decimal.fromUserInput("1", 7))).toThrowError(/do not match/i);
+      // original value remain unchanged
+      expect(zero.toString()).toEqual("0");
+      expect(one.toString()).toEqual("1");
+      expect(oneDotFive.toString()).toEqual("1.5");
     });
   });
 

diff --git a/packages/math/src/decimal.ts b/packages/math/src/decimal.ts
@@ -1,5 +1,7 @@
 import BN from "bn.js";
 
+import { Uint32, Uint53, Uint64 } from "./integers";
+
 // Too large values lead to massive memory usage. Limit to something sensible.
 // The largest value we need is 18 (Ether).
 const maxFractionalDigits = 100;
@@ -127,12 +129,10 @@ export class Decimal {
   /**
    * a.multiply(b) returns a*b.
    *
-   * Both values need to have the same fractional digits.
+   * We only allow multiplication by unsigned integers to avoid rounding errors.
    */
-  public multiply(b: Decimal): Decimal {
-    if (this.fractionalDigits !== b.fractionalDigits) throw new Error("Fractional digits do not match");
-    const factor = new BN(10).pow(new BN(this.data.fractionalDigits));
-    const product = this.data.atomics.mul(new BN(b.atomics)).div(factor);
+  public multiply(b: Uint32 | Uint53 | Uint64): Decimal {
+    const product = this.data.atomics.mul(new BN(b.toString()));
     return new Decimal(product.toString(), this.fractionalDigits);
   }
 

diff --git a/packages/math/types/decimal.d.ts b/packages/math/types/decimal.d.ts
@@ -1,3 +1,4 @@
+import { Uint32, Uint53, Uint64 } from "./integers";
 /**
  * A type for arbitrary precision, non-negative decimals.
  *
@@ -27,9 +28,9 @@ export declare class Decimal {
   /**
    * a.multiply(b) returns a*b.
    *
-   * Both values need to have the same fractional digits.
+   * We only allow multiplication by unsigned integers to avoid rounding errors.
    */
-  multiply(b: Decimal): Decimal;
+  multiply(b: Uint32 | Uint53 | Uint64): Decimal;
   equals(b: Decimal): boolean;
   isLessThan(b: Decimal): boolean;
   isLessThanOrEqual(b: Decimal): boolean;