New prng

src/engine/PRNG.ts

@@ -1,16 +1,26 @@
-// Taken from https://gist.github.com/blixt/f17b47c62508be59987b
+// Taken from https://github.com/bryc/code/blob/master/jshash/PRNGs.md
 // Ink uses a seedable PRNG of which there is none in native javascript.
 export class PRNG {
   private seed: number;
 
   constructor(seed: number) {
-    this.seed = seed % 2147483647;
-    if (this.seed <= 0) this.seed += 2147483646;
+    this.seed = seed;
+  }
+
+  public nextSeed(): number {
+    let a = this.seed;
+    a |= 0;
+    a = (a + 0x6d2b79f5) | 0;
+    this.seed = a;
+    return a;
   }
   public next(): number {
-    return (this.seed = (this.seed * 16807) % 2147483647);
+    let a = this.seed;
+    let t = Math.imul(a ^ (a >>> 15), 1 | a);
+    t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t;
+    return (t ^ (t >>> 14)) >>> 0;
   }
   public nextFloat(): number {
-    return (this.next() - 1) / 2147483646;
+    return this.next() / 4294967296;
   }
 }

src/engine/Story.ts

@@ -1189,15 +1189,15 @@ export class Story extends InkObject {
                 ". The maximum must be larger"
             );
 
-          let resultSeed = this.state.storySeed + this.state.previousRandom;
+          let resultSeed = this.state.previousRandom;
           let random = new PRNG(resultSeed);
 
           let nextRandom = random.next();
           let chosenValue = (nextRandom % randomRange) + minInt.value;
           this.state.PushEvaluationStack(new IntValue(chosenValue));
 
           // Next random number (rather than keeping the Random object around)
-          this.state.previousRandom = nextRandom;
+          this.state.previousRandom = random.nextSeed();
           break;
         }
 
@@ -1212,8 +1212,7 @@ export class Story extends InkObject {
             return throwNullException("minInt.value");
           }
 
-          this.state.storySeed = seed.value;
-          this.state.previousRandom = 0;
+          this.state.previousRandom = seed.value;
 
           this.state.PushEvaluationStack(new Void());
           break;
@@ -1349,7 +1348,7 @@ export class Story extends InkObject {
             newList = new InkList();
           } else {
             // Generate a random index for the element to take
-            let resultSeed = this.state.storySeed + this.state.previousRandom;
+            let resultSeed = this.state.previousRandom;
             let random = new PRNG(resultSeed);
 
             let nextRandom = random.next();
@@ -1377,7 +1376,7 @@ export class Story extends InkObject {
             newList = new InkList(randomItem.Key.originName, this);
             newList.Add(randomItem.Key, randomItem.Value);
 
-            this.state.previousRandom = nextRandom;
+            this.state.previousRandom = random.nextSeed();
           }
 
           this.state.PushEvaluationStack(new ListValue(newList));
@@ -2092,7 +2091,9 @@ export class Story extends InkObject {
     }
 
     for (let i = 0; i <= iterationIndex; ++i) {
-      let chosen = random.next() % unpickedIndices.length;
+      let nextRandom = random.next();
+      let chosen = nextRandom % unpickedIndices.length;
+      random.nextSeed();
       let chosenIndex = unpickedIndices[chosen];
       unpickedIndices.splice(chosen, 1);
 

src/engine/StoryState.ts

@@ -350,9 +350,9 @@ export class StoryState {
     this._turnIndices = new Map();
     this.currentTurnIndex = -1;
 
-    let timeSeed = new Date().getTime();
-    this.storySeed = new PRNG(timeSeed).next() % 100;
-    this.previousRandom = 0;
+    let timeSeed = Date.now();
+    this.storySeed = new PRNG(timeSeed).nextSeed();
+    this.previousRandom = this.storySeed;
 
     this._currentChoices = [];