From 2fdddbc129b7621737a9fc75b63b34021352e70a Mon Sep 17 00:00:00 2001
From: Sam HADOW <sam.hadow@inbox.lv>
Date: Tue, 23 Dec 2025 23:03:22 +0100
Subject: [PATCH] fermat primality test

---
 fermat-prime-test.hs | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
 create mode 100644 fermat-prime-test.hs

diff --git a/fermat-prime-test.hs b/fermat-prime-test.hs
new file mode 100644
index 0000000..ec99576
--- /dev/null
+++ b/fermat-prime-test.hs
@@ -0,0 +1,15 @@
+import System.Random (randomRIO)
+import ModularArithmeticUtils (modExp)
+
+fermatPrimeTest :: Integer -> Integer -> IO Bool
+fermatPrimeTest n k
+  | n <= 3    = return (n == 2 || n == 3)
+  | even n    = return False
+  | otherwise = go k
+  where
+    go 0 = return True
+    go i = do
+      a <- randomRIO (2, n - 2)
+      if modExp a (n - 1) n /= 1
+        then return False
+        else go (i - 1)