✨ Clone from state on mersenne (#698)

Follow-up of #694

src/generator/MersenneTwister.ts

@@ -73,8 +73,27 @@ class MersenneTwister implements RandomGenerator {
     }
     return y;
   }
+
+  getState(): readonly number[] {
+    return [this.index, ...this.states];
+  }
+
+  public static fromState(state: readonly number[]): MersenneTwister {
+    const valid = state.length === MersenneTwister.N + 1 && state[0] >= 0 && state[0] < MersenneTwister.N;
+    if (!valid) {
+      throw new Error('The state must have been produced by a mersenne RandomGenerator');
+    }
+    return new MersenneTwister(state.slice(1), state[0]);
+  }
 }
 
-export default function (seed: number): RandomGenerator {
-  return MersenneTwister.from(seed);
+function fromState(state: readonly number[]): RandomGenerator {
+  return MersenneTwister.fromState(state);
 }
+
+export default Object.assign(
+  function (seed: number): RandomGenerator {
+    return MersenneTwister.from(seed);
+  },
+  { fromState },
+);

test/unit/generator/MersenneTwister.spec.ts

@@ -136,6 +136,8 @@ describe('mersenne', () => {
     );
   });
   it('Should return the same sequence given same seeds', () => fc.assert(p.sameSeedSameSequences(mersenne)));
+  it('Should return the same sequence when built from state', () =>
+    fc.assert(p.clonedFromStateSameSequences(mersenne)));
   it('Should return the same sequence if called twice', () => fc.assert(p.sameSequencesIfCallTwice(mersenne)));
   it('Should generate values between -2**31 and 2**31 -1', () => fc.assert(p.valuesInRange(mersenne)));
   it('Should impact itself with unsafeNext', () => fc.assert(p.changeSelfWithUnsafeNext(mersenne)));