Change PRNG to BigInt version.

1 files changed, 5 insertions, 1 deletions

diff --git a/rules.js b/rules.js
index fcdc1ec..a44fd4f 100644
--- a/rules.js
+++ b/rules.js
@@ -61,7 +61,11 @@ const RESERVE_MARK = ""
 let game = null
 
 function random(n) {
-	return (game.seed = game.seed * 200105 % 34359738337) % n
+	// Largest MLCG that will fit its state in a double.
+	// Uses BigInt for arithmetic, so is an order of magnitude slower.
+	// https://www.ams.org/journals/mcom/1999-68-225/S0025-5718-99-00996-5/S0025-5718-99-00996-5.pdf
+	// m = 2**53 - 111
+	return (game.seed = Number(BigInt(game.seed) * 5667072534355537n % 9007199254740881n)) % n
 }
 
 function logbr() {