✨ Clone from state on xorshift128plus (#697)

Follow-up of #694
dubzzz · Mar 20, 2024 · c60c828 · c60c828
1 parent 6a16bfe
commit c60c828
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Showing 2 changed files with 19 additions and 3 deletions.
diff --git a/src/generator/XorShift.ts b/src/generator/XorShift.ts
@@ -64,8 +64,22 @@ class XorShift128Plus implements RandomGenerator {
     this.s11 = ns11;
     this.s10 = ns10;
   }
+  getState(): readonly number[] {
+    return [this.s01, this.s00, this.s11, this.s10];
+  }
+}
+
+function fromState(state: readonly number[]): RandomGenerator {
+  const valid = state.length === 4;
+  if (!valid) {
+    throw new Error('The state must have been produced by a xorshift128plus RandomGenerator');
+  }
+  return new XorShift128Plus(state[0], state[1], state[2], state[3]);
 }
 
-export const xorshift128plus = function (seed: number): RandomGenerator {
-  return new XorShift128Plus(-1, ~seed, seed | 0, 0);
-};
+export const xorshift128plus = Object.assign(
+  function (seed: number): RandomGenerator {
+    return new XorShift128Plus(-1, ~seed, seed | 0, 0);
+  },
+  { fromState },
+);
diff --git a/test/unit/generator/XorShift.spec.ts b/test/unit/generator/XorShift.spec.ts
@@ -92,6 +92,8 @@ describe('xorshift128plus', () => {
     );
   });
   it('Should return the same sequence given same seeds', () => fc.assert(p.sameSeedSameSequences(xorshift128plus)));
+  it('Should return the same sequence when built from state', () =>
+    fc.assert(p.clonedFromStateSameSequences(xorshift128plus)));
   it('Should return the same sequence if called twice', () => fc.assert(p.sameSequencesIfCallTwice(xorshift128plus)));
   it('Should generate values between -2**31 and 2**31 -1', () => fc.assert(p.valuesInRange(xorshift128plus)));
   it('Should not depend on ordering between jump and next', () => fc.assert(p.noOrderNextJump(xorshift128plus)));