refactor(mersenne): rewrite internal mersenne (#1447)

3 files changed, 42 insertions, 76 deletions

diff --git a/src/faker.ts b/src/faker.ts
index f8a46511..fd7ed522 100644
--- a/src/faker.ts
+++ b/src/faker.ts
@@ -1,7 +1,8 @@
 import type { LocaleDefinition } from './definitions';
 import { FakerError } from './errors/faker-error';
 import { deprecated } from './internal/deprecated';
-import { MersenneModule } from './internal/mersenne/mersenne';
+import type { Mersenne } from './internal/mersenne/mersenne';
+import mersenne from './internal/mersenne/mersenne';
 import type { KnownLocale } from './locales';
 import { AnimalModule } from './modules/animal';
 import { ColorModule } from './modules/color';
@@ -79,7 +80,7 @@ export class Faker {
   readonly definitions: LocaleDefinition = this.initDefinitions();
 
   /** @internal */
-  private readonly _mersenne: MersenneModule = new MersenneModule();
+  private readonly _mersenne: Mersenne = mersenne();
 
   readonly random: RandomModule = new RandomModule(this);
 
@@ -286,11 +287,7 @@ export class Faker {
   seed(
     seed: number | number[] = Math.ceil(Math.random() * Number.MAX_SAFE_INTEGER)
   ): number | number[] {
-    if (Array.isArray(seed) && seed.length) {
-      this._mersenne.seed_array(seed);
-    } else if (!Array.isArray(seed) && !isNaN(seed)) {
-      this._mersenne.seed(seed);
-    }
+    this._mersenne.seed(seed);
 
     return seed;
   }
diff --git a/src/internal/mersenne/mersenne.ts b/src/internal/mersenne/mersenne.ts
index 16019e29..e7c0355c 100644
--- a/src/internal/mersenne/mersenne.ts
+++ b/src/internal/mersenne/mersenne.ts
@@ -1,81 +1,49 @@
-import { FakerError } from '../../errors/faker-error';
-import Gen from './twister';
+import Twister from './twister';
 
 /**
- * Module to generate seed based random numbers.
+ * Generate seed based random numbers.
  *
  * @internal
  */
-export class MersenneModule {
-  private gen = new Gen();
-
-  constructor() {
-    this.gen.initGenrand(Math.ceil(Math.random() * Number.MAX_SAFE_INTEGER));
-
-    // Bind `this` so namespaced is working correctly
-    for (const name of Object.getOwnPropertyNames(MersenneModule.prototype)) {
-      if (name === 'constructor' || typeof this[name] !== 'function') {
-        continue;
-      }
-      this[name] = this[name].bind(this);
-    }
-  }
-
+export interface Mersenne {
   /**
-   * Generates a random number between `[min, max)`.
-   *
-   * @param max The maximum number. Defaults to `32768`.
-   * @param min The minimum number. Defaults to `0`.
+   * Generates a random number between `[min, max)`. The result is already floored.
    *
-   * @example
-   * faker.mersenne.rand() // 15515
-   * faker.mersenne.rand(1000, 500) // 578
-   *
-   * @since 5.5.0
+   * @param options The options to generate a random number.
+   * @param options.min The minimum number.
+   * @param options.max The maximum number.
    */
-  rand(max = 32768, min = 0): number {
-    if (min > max) {
-      const temp = min;
-      min = max;
-      max = temp;
-    }
-
-    return Math.floor(this.gen.genrandReal2() * (max - min) + min);
-  }
+  next(options: { max: number; min: number }): number;
 
   /**
    * Sets the seed to use.
    *
-   * @param S The seed to use.
-   * @throws If the seed is not a `number`.
-   *
-   * @since 5.5.0
+   * @param seed The seed to use.
    */
-  seed(S: number): void {
-    if (typeof S !== 'number') {
-      throw new FakerError(
-        `seed(S) must take numeric argument; is ${typeof S}`
-      );
-    }
+  seed(seed: number | number[]): void;
+}
+
+/**
+ * Generate seed based random numbers.
+ *
+ * @internal
+ */
+export default function mersenne(): Mersenne {
+  const twister = new Twister();
 
-    this.gen.initGenrand(S);
-  }
+  twister.initGenrand(Math.ceil(Math.random() * Number.MAX_SAFE_INTEGER));
 
-  /**
-   * Sets the seed to use.
-   *
-   * @param A The seed to use.
-   * @throws If the seed is not a `number[]`.
-   *
-   * @since 5.5.0
-   */
-  seed_array(A: number[]): void {
-    if (typeof A !== 'object') {
-      throw new FakerError(
-        `seed_array(A) must take array of numbers; is ${typeof A}`
-      );
-    }
+  return {
+    next({ min, max }): number {
+      return Math.floor(twister.genrandReal2() * (max - min) + min);
+    },
 
-    this.gen.initByArray(A, A.length);
-  }
+    seed(seed: number | number[]): void {
+      if (typeof seed === 'number') {
+        twister.initGenrand(seed);
+      } else if (Array.isArray(seed)) {
+        twister.initByArray(seed, seed.length);
+      }
+    },
+  };
 }
diff --git a/src/modules/datatype/index.ts b/src/modules/datatype/index.ts
index 41c5c3e4..d4fcbbd6 100644
--- a/src/modules/datatype/index.ts
+++ b/src/modules/datatype/index.ts
@@ -1,7 +1,7 @@
 import type { Faker } from '../..';
 import { FakerError } from '../../errors/faker-error';
 import { deprecated } from '../../internal/deprecated';
-import type { MersenneModule } from '../../internal/mersenne/mersenne';
+import type { Mersenne } from '../../internal/mersenne/mersenne';
 
 /**
  * Module to generate various primitive values and data types.
@@ -56,13 +56,14 @@ export class DatatypeModule {
       throw new FakerError(`Max ${max} should be greater than min ${min}.`);
     }
 
-    const mersenne: MersenneModule =
+    const mersenne: Mersenne =
       // @ts-expect-error: access private member field
       this.faker._mersenne;
 
-    const randomNumber = Math.floor(
-      mersenne.rand(max / precision + 1, min / precision)
-    );
+    const randomNumber = mersenne.next({
+      min: min / precision,
+      max: max / precision + 1,
+    });
 
     // Workaround problem in float point arithmetics for e.g. 6681493 / 0.01
     return randomNumber / (1 / precision);