WIP

Author: jessealama

src/Decimal.mts

@@ -0,0 +1,79 @@
+import { Rational } from "./rational.mjs";
+
+function _cohort(s: string): "0" | "-0" | Rational {
+    if (s === "0" || s === "-0") {
+        return s;
+    }
+
+    return Rational.fromString(s);
+}
+
+function _quantum(s: string): number {
+    if (s.match(/^-/)) {
+        return _quantum(s.substring(1));
+    }
+
+    if (!s.match(/[.]/)) {
+        return 0;
+    }
+
+    let [_, rhs] = s.split(".");
+
+    if (rhs.match(/[eE]/)) {
+        let [dec, exp] = rhs.split(/[eE]/);
+        return parseInt(exp) - dec.length;
+    }
+
+    return 0 - rhs.length;
+}
+
+interface CohortAndQuantum {
+    cohort: "0" | "-0" | Rational;
+    quantum: number;
+}
+
+export class Decimal {
+    public readonly cohort: "0" | "-0" | Rational;
+    public readonly quantum: number;
+
+    constructor(x: string | CohortAndQuantum) {
+        let v = typeof x === "string" ? _cohort(x) : x.cohort;
+        let q = typeof x === "string" ? _quantum(x) : x.quantum;
+
+        if (v instanceof Rational && v.isZero()) {
+            throw new RangeError("A rational number cohort must not be zero.");
+        }
+
+        if (!Number.isInteger(q)) {
+            throw new Error("The quantum must be an integer.");
+        }
+
+        if (v instanceof Rational) {
+            let scaledV = v.scale10(0 - q);
+
+            if (!scaledV.isInteger()) {
+                throw new RangeError(
+                    `Scaled value is not an integer (v = ${v}, q = ${q})`
+                );
+            }
+        }
+
+        this.cohort = v;
+        this.quantum = q;
+    }
+
+    public isZero(): boolean {
+        let v = this.cohort;
+        return v === "0" || v === "-0";
+    }
+
+    public isInteger(): boolean {
+        let v = this.cohort;
+
+        if (v === "0" || v === "-0") {
+            return true;
+        }
+
+        return v.isInteger();
+    }
+}

src/common.mts

@@ -1,3 +1,10 @@
+import {
+    ROUNDING_MODE_CEILING,
+    ROUNDING_MODE_FLOOR,
+    ROUNDING_MODE_HALF_EXPAND,
+    ROUNDING_MODE_TRUNCATE,
+} from "./decimal128.mjs";
+
 /**
  * Counts the number of significant digits in a digit string, assumed to be normalized.
  *
@@ -33,7 +40,7 @@ export function countDigits(s: string): number {
     return s.replace(/[.]/, "").length;
 }
 
-export function countFractionaDigits(s: string): number {
+export function countFractionalDigits(s: string): number {
     let [, fractional] = s.split(".");
 
     if (undefined === fractional) {
@@ -60,3 +67,55 @@ export const ROUNDING_MODES: RoundingMode[] = [
     "halfEven",
     "halfExpand",
 ];
+
+function roundIt(
+    isNegative: boolean,
+    digitToRound: Digit,
+    decidingDigit: Digit,
+    roundingMode: RoundingMode
+): DigitOrTen {
+    switch (roundingMode) {
+        case ROUNDING_MODE_CEILING:
+            if (isNegative) {
+                return digitToRound;
+            }
+
+            if (0 === decidingDigit) {
+                return digitToRound;
+            }
+
+            return (digitToRound + 1) as DigitOrTen;
+        case ROUNDING_MODE_FLOOR:
+            if (0 === decidingDigit) {
+                return digitToRound;
+            }
+
+            if (isNegative) {
+                return (digitToRound + 1) as DigitOrTen;
+            }
+
+            return digitToRound;
+        case ROUNDING_MODE_TRUNCATE:
+            return digitToRound;
+        case ROUNDING_MODE_HALF_EXPAND:
+            if (decidingDigit >= 5) {
+                return (digitToRound + 1) as DigitOrTen;
+            }
+
+            return digitToRound;
+        default: // ROUNDING_MODE_HALF_EVEN:
+            if (decidingDigit === 5) {
+                if (digitToRound % 2 === 0) {
+                    return digitToRound;
+                }
+
+                return (digitToRound + 1) as DigitOrTen;
+            }
+
+            if (decidingDigit > 5) {
+                return (digitToRound + 1) as DigitOrTen;
+            }
+
+            return digitToRound;
+    }
+}