⚡️ Faster uniform distribution on small ranges (#516)

dubzzz · Jan 9, 2023 · 464960a · 464960a
1 parent a7e19a8
commit 464960a
Showing 1 changed file with 4 additions and 7 deletions.
diff --git a/src/distribution/internals/UnsafeUniformIntDistributionInternal.ts b/src/distribution/internals/UnsafeUniformIntDistributionInternal.ts
@@ -6,15 +6,12 @@ import { RandomGenerator } from '../../generator/RandomGenerator';
  * @internal
  */
 export function unsafeUniformIntDistributionInternal(rangeSize: number, rng: RandomGenerator): number {
-  const MinRng = -0x80000000;
-  const NumValues = 0x100000000;
-
   // Range provided by the RandomGenerator is large enough,
   // given rangeSize <= 0x100000000 and RandomGenerator is uniform on 0x100000000 values
-  const MaxAllowed = NumValues - (NumValues % rangeSize);
-  let deltaV = rng.unsafeNext() - MinRng;
+  const MaxAllowed = rangeSize > 2 ? ~~(0x100000000 / rangeSize) * rangeSize : 0x100000000;
+  let deltaV = rng.unsafeNext() + 0x80000000;
   while (deltaV >= MaxAllowed) {
-    deltaV = rng.unsafeNext() - MinRng;
+    deltaV = rng.unsafeNext() + 0x80000000;
   }
-  return deltaV % rangeSize; // Warning: we expect NumValues <= 2**32, so diff too
+  return deltaV % rangeSize;
 }