Merge branch '0.22'

packages/math/src/decimal.spec.ts

@@ -212,6 +212,54 @@ describe("Decimal", () => {
     });
   });
 
+  describe("minus", () => {
+    it("returns correct values", () => {
+      const zero = Decimal.fromUserInput("0", 5);
+      expect(Decimal.fromUserInput("0", 5).minus(zero).toString()).toEqual("0");
+      expect(Decimal.fromUserInput("1", 5).minus(zero).toString()).toEqual("1");
+      expect(Decimal.fromUserInput("2", 5).minus(zero).toString()).toEqual("2");
+      expect(Decimal.fromUserInput("2.8", 5).minus(zero).toString()).toEqual("2.8");
+      expect(Decimal.fromUserInput("0.12345", 5).minus(zero).toString()).toEqual("0.12345");
+
+      const one = Decimal.fromUserInput("1", 5);
+      expect(Decimal.fromUserInput("1", 5).minus(one).toString()).toEqual("0");
+      expect(Decimal.fromUserInput("2", 5).minus(one).toString()).toEqual("1");
+      expect(Decimal.fromUserInput("3", 5).minus(one).toString()).toEqual("2");
+      expect(Decimal.fromUserInput("3.8", 5).minus(one).toString()).toEqual("2.8");
+      expect(Decimal.fromUserInput("1.12345", 5).minus(one).toString()).toEqual("0.12345");
+
+      const oneDotFive = Decimal.fromUserInput("1.5", 5);
+      expect(Decimal.fromUserInput("1.5", 5).minus(oneDotFive).toString()).toEqual("0");
+      expect(Decimal.fromUserInput("2.5", 5).minus(oneDotFive).toString()).toEqual("1");
+      expect(Decimal.fromUserInput("3.5", 5).minus(oneDotFive).toString()).toEqual("2");
+      expect(Decimal.fromUserInput("4.3", 5).minus(oneDotFive).toString()).toEqual("2.8");
+      expect(Decimal.fromUserInput("1.62345", 5).minus(oneDotFive).toString()).toEqual("0.12345");
+
+      // 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", () => {
+      const zero = Decimal.fromUserInput("0", 5);
+      expect(() => Decimal.fromUserInput("1", 1).minus(zero)).toThrowError(/do not match/i);
+      expect(() => Decimal.fromUserInput("1", 2).minus(zero)).toThrowError(/do not match/i);
+      expect(() => Decimal.fromUserInput("1", 3).minus(zero)).toThrowError(/do not match/i);
+      expect(() => Decimal.fromUserInput("1", 4).minus(zero)).toThrowError(/do not match/i);
+
+      expect(() => Decimal.fromUserInput("1", 6).minus(zero)).toThrowError(/do not match/i);
+      expect(() => Decimal.fromUserInput("1", 7).minus(zero)).toThrowError(/do not match/i);
+    });
+
+    it("throws for negative results", () => {
+      const one = Decimal.fromUserInput("1", 5);
+      expect(() => Decimal.fromUserInput("0", 5).minus(one)).toThrowError(/must not be negative/i);
+      expect(() => Decimal.fromUserInput("0.5", 5).minus(one)).toThrowError(/must not be negative/i);
+      expect(() => Decimal.fromUserInput("0.98765", 5).minus(one)).toThrowError(/must not be negative/i);
+    });
+  });
+
   describe("multiply", () => {
     it("returns correct values for Uint32", () => {
       const zero = Decimal.fromUserInput("0", 5);

packages/math/src/decimal.ts

@@ -126,6 +126,19 @@ export class Decimal {
     return new Decimal(sum.toString(), this.fractionalDigits);
   }
 
+  /**
+   * a.minus(b) returns a-b.
+   *
+   * Both values need to have the same fractional digits.
+   * The resulting difference needs to be non-negative.
+   */
+  public minus(b: Decimal): Decimal {
+    if (this.fractionalDigits !== b.fractionalDigits) throw new Error("Fractional digits do not match");
+    const difference = this.data.atomics.sub(new BN(b.atomics));
+    if (difference.ltn(0)) throw new Error("Difference must not be negative");
+    return new Decimal(difference.toString(), this.fractionalDigits);
+  }
+
   /**
    * a.multiply(b) returns a*b.
    *