Category talk:Wren-big: Difference between revisions

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@@ Line 967: / Line 967: @@
     }
+    // Returns the previous probable prime number less than 'this' or null if there isn't one.
-    // Convenience version of the above method which uses 5 iterations.
+    prevPrime(iterations) {
+        if (this < BigInt.three) return null
+        if (this == BigInt.three) return BigInt.two
+        var n = isEven ? this - 1 : this - 2
+        while (true) {
+            if (n.isProbablePrime(iterations)) return n
+            n = n - 2
+        }
+    }
+    // Convenience versions of the above methods which use 5 iterations.
     nextPrime { nextPrime(5) }
+    prevPrime { prevPrime(5) }
     // Negates a BigInt.