refactoring primeFactors

vitaly-t · Nov 2, 2021 · 2742c60 · 2742c60
1 parent b93e931
commit 2742c60
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Showing 3 changed files with 38 additions and 44 deletions.
diff --git a/package.json b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "prime-lib",
-  "version": "0.4.3",
+  "version": "0.4.4",
   "description": "Prime number library",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",

diff --git a/src/prime-factors.ts b/src/prime-factors.ts
@@ -1,71 +1,70 @@
 /**
  * Calculates prime factorization of a number.
  *
- * Works up to the maximum of 9007199254740991
+ * Works up to 2^53 - 1 = 9_007_199_254_740_991
  *
- * This is a draft for high-performance calculation that passes all tests.
- * It just needs a bit of good refactoring.
+ * TODO: This is a draft for high-performance calculation.
+ *       It still needs a bit of refactoring + tests.
  */
-
-let numLeft: number;
-
-const my = {
-    FArr: new Array<number>(),
-    MAX: 9007199254740991,
-    lowPrimes: getLowPrimes(),
-    lowPrimeN: 100
-};
-
-export function primeFactors(TheNum: number) {
-    my.FArr = [];
-    if (TheNum > my.MAX) {
-        return my.FArr;
+export function primeFactors(x: number): number[] {
+    cfg.result = [];
+    if (x > cfg.max) {
+        return cfg.result;
     }
-    numLeft = TheNum;
-    if (numLeft === 0 || numLeft === 1) {
-        return my.FArr;
+    cfg.numLeft = x;
+    if (cfg.numLeft === 0 || cfg.numLeft === 1) {
+        return cfg.result;
     }
-    let doneQ = false;
-    for (var p = 0; p < my.lowPrimeN; p++) {
-        if (!testFact(my.lowPrimes[p])) {
+    let doneQ = false, p = 0;
+    for (p; p < cfg.lowPrimeN; p++) {
+        if (!testFact(cfg.lowPrimes[p])) {
             doneQ = true;
             break;
         }
     }
     if (!doneQ) {
-        let fact = (((my.lowPrimes[p - 1] + 5) / 6) << 0) * 6 - 1;
+        let fact = (((cfg.lowPrimes[p - 1] + 5) / 6) << 0) * 6 - 1;
         while (true) {
-            if (!testFact(fact)) break;
+            if (!testFact(fact)) {
+                break;
+            }
             fact += 2;
-            if (!testFact(fact)) break;
+            if (!testFact(fact)) {
+                break;
+            }
             fact += 4;
         }
     }
-    if (numLeft !== 1) addFact(numLeft, 1);
-
-    return my.FArr;
+    if (cfg.numLeft !== 1) {
+        addFact(cfg.numLeft, 1);
+    }
+    return cfg.result;
 }
 
 function testFact(fact: number): boolean {
     let power = 0;
-    while (numLeft % fact === 0) {
+    while (cfg.numLeft % fact === 0) {
         power++;
-        numLeft = numLeft / fact;
+        cfg.numLeft = cfg.numLeft / fact;
     }
     if (power !== 0) {
         addFact(fact, power);
     }
-    return numLeft / fact > fact;
+    return cfg.numLeft / fact > fact;
 }
 
-function addFact(fact: number, power: number) {
+function addFact(fact: number, power: number): void {
     for (let i = 0; i < power; i++) {
-        my.FArr.push(fact);
+        cfg.result.push(fact);
     }
 }
 
-function getLowPrimes() {
-    return [
+const cfg = {
+    result: [] as number[],
+    max: 9007199254740991, // = 2^53 - 1
+    numLeft: 0,
+    lowPrimeN: 100,
+    lowPrimes: [
         2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109,
         113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239,
         241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379,
@@ -74,5 +73,5 @@ function getLowPrimes() {
         673, 677, 683, 691, 701, 709, 719, 727, 733, 739, 743, 751, 757, 761, 769, 773, 787, 797, 809, 811, 821, 823, 827,
         829, 839, 853, 857, 859, 863, 877, 881, 883, 887, 907, 911, 919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991,
         997, 1009, 1013, 1019, 1021, 1031, 1033, 1039
-    ];
-}
+    ]
+};
diff --git a/test/prime-factors.spec.ts b/test/prime-factors.spec.ts
@@ -22,11 +22,6 @@ describe('primeFactors', () => {
         expect(primeFactors(600_851_475_143)).to.eql([71, 839, 1471, 6857]);
     });
     it('must handle large complex numbers', () => {
-        // TODO: This doesn't work currently (dead slow)
-        //  1125899906842622 = 2 ** 50 - 2
-        //  calculators where it works well:
-        //  - https://www.mathsisfun.com/numbers/prime-factorization-tool.html
-        //  - https://www.omnicalculator.com/math/prime-factorization
         expect(primeFactors(1_125_899_906_842_622)).to.eql([2, 127, 4432676798593]);
     });
 });