From fe5019808617292d12328ee656606b92b866c014 Mon Sep 17 00:00:00 2001
From: Simon Warta <simon@warta.it>
Date: Tue, 26 Apr 2022 17:05:27 +0200
Subject: [PATCH] Add Decimal.floor/.ceil

---
 CHANGELOG.md                      |  4 ++++
 packages/math/src/decimal.spec.ts | 36 +++++++++++++++++++++++++++++++
 packages/math/src/decimal.ts      | 31 ++++++++++++++++++++++++++
 3 files changed, 71 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 857340fe8e..9dc2be2b4a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,10 @@ and this project adheres to
 
 ## [Unreleased]
 
+### Added
+
+- @cosmjs/math: Add `Decimal.floor` and `Decimal.ceil`.
+
 ## [0.28.4] - 2022-04-15
 
 ### Added
diff --git a/packages/math/src/decimal.spec.ts b/packages/math/src/decimal.spec.ts
index 1526c9260e..52b876f7d5 100644
--- a/packages/math/src/decimal.spec.ts
+++ b/packages/math/src/decimal.spec.ts
@@ -177,6 +177,42 @@ describe("Decimal", () => {
     });
   });
 
+  describe("floor", () => {
+    it("works", () => {
+      // whole numbers
+      expect(Decimal.fromUserInput("0", 0).floor().toString()).toEqual("0");
+      expect(Decimal.fromUserInput("1", 0).floor().toString()).toEqual("1");
+      expect(Decimal.fromUserInput("44", 0).floor().toString()).toEqual("44");
+      expect(Decimal.fromUserInput("0", 3).floor().toString()).toEqual("0");
+      expect(Decimal.fromUserInput("1", 3).floor().toString()).toEqual("1");
+      expect(Decimal.fromUserInput("44", 3).floor().toString()).toEqual("44");
+
+      // with fractional part
+      expect(Decimal.fromUserInput("0.001", 3).floor().toString()).toEqual("0");
+      expect(Decimal.fromUserInput("1.999", 3).floor().toString()).toEqual("1");
+      expect(Decimal.fromUserInput("0.000000000000000001", 18).floor().toString()).toEqual("0");
+      expect(Decimal.fromUserInput("1.999999999999999999", 18).floor().toString()).toEqual("1");
+    });
+  });
+
+  describe("ceil", () => {
+    it("works", () => {
+      // whole numbers
+      expect(Decimal.fromUserInput("0", 0).ceil().toString()).toEqual("0");
+      expect(Decimal.fromUserInput("1", 0).ceil().toString()).toEqual("1");
+      expect(Decimal.fromUserInput("44", 0).ceil().toString()).toEqual("44");
+      expect(Decimal.fromUserInput("0", 3).ceil().toString()).toEqual("0");
+      expect(Decimal.fromUserInput("1", 3).ceil().toString()).toEqual("1");
+      expect(Decimal.fromUserInput("44", 3).ceil().toString()).toEqual("44");
+
+      // with fractional part
+      expect(Decimal.fromUserInput("0.001", 3).ceil().toString()).toEqual("1");
+      expect(Decimal.fromUserInput("1.999", 3).ceil().toString()).toEqual("2");
+      expect(Decimal.fromUserInput("0.000000000000000001", 18).ceil().toString()).toEqual("1");
+      expect(Decimal.fromUserInput("1.999999999999999999", 18).ceil().toString()).toEqual("2");
+    });
+  });
+
   describe("toString", () => {
     it("displays no decimal point for full numbers", () => {
       expect(Decimal.fromUserInput("44", 0).toString()).toEqual("44");
diff --git a/packages/math/src/decimal.ts b/packages/math/src/decimal.ts
index 6bb8a1f69a..91ec2cc181 100644
--- a/packages/math/src/decimal.ts
+++ b/packages/math/src/decimal.ts
@@ -113,6 +113,37 @@ export class Decimal {
     };
   }
 
+  /** Creates a new instance with the same value */
+  private clone(): Decimal {
+    return new Decimal(this.atomics, this.fractionalDigits);
+  }
+
+  /** Returns the greatest decimal <= this which has no fractional part (rounding down) */
+  public floor(): Decimal {
+    const factor = new BN(10).pow(new BN(this.data.fractionalDigits));
+    const whole = this.data.atomics.div(factor);
+    const fractional = this.data.atomics.mod(factor);
+
+    if (fractional.isZero()) {
+      return this.clone();
+    } else {
+      return Decimal.fromAtomics(whole.mul(factor).toString(), this.fractionalDigits);
+    }
+  }
+
+  /** Returns the smallest decimal >= this which has no fractional part (rounding up) */
+  public ceil(): Decimal {
+    const factor = new BN(10).pow(new BN(this.data.fractionalDigits));
+    const whole = this.data.atomics.div(factor);
+    const fractional = this.data.atomics.mod(factor);
+
+    if (fractional.isZero()) {
+      return this.clone();
+    } else {
+      return Decimal.fromAtomics(whole.addn(1).mul(factor).toString(), this.fractionalDigits);
+    }
+  }
+
   public toString(): string {
     const factor = new BN(10).pow(new BN(this.data.fractionalDigits));
     const whole = this.data.atomics.div(factor);