Data commit

Task/Modular-exponentiation/Common-Lisp/modular-exponentiation-1.lisp

@@ -0,0 +1,18 @@
+(defun rosetta-mod-expt (base power divisor)
+  "Return BASE raised to the POWER, modulo DIVISOR.
+  This function is faster than (MOD (EXPT BASE POWER) DIVISOR), but
+  only works when POWER is a non-negative integer."
+  (setq base (mod base divisor))
+  ;; Multiply product with base until power is zero.
+  (do ((product 1))
+      ((zerop power) product)
+    ;; Square base, and divide power by 2, until power becomes odd.
+    (do () ((oddp power))
+      (setq base (mod (* base base) divisor)
+	    power (ash power -1)))
+    (setq product (mod (* product base) divisor)
+	  power (1- power))))
+
+(let ((a 2988348162058574136915891421498819466320163312926952423791023078876139)
+      (b 2351399303373464486466122544523690094744975233415544072992656881240319))
+  (format t "~A~%" (rosetta-mod-expt a b (expt 10 40))))

Task/Modular-exponentiation/Common-Lisp/modular-exponentiation-2.lisp

@@ -0,0 +1,4 @@
+;; CLISP provides EXT:MOD-EXPT
+(let ((a 2988348162058574136915891421498819466320163312926952423791023078876139)
+      (b 2351399303373464486466122544523690094744975233415544072992656881240319))
+  (format t "~A~%" (mod-expt a b (expt 10 40))))

Task/Modular-exponentiation/Common-Lisp/modular-exponentiation-3.lisp

@@ -0,0 +1,6 @@
+(defun mod-expt (a n m)
+   (loop with c = 1 while (plusp n) do
+      (if (oddp n) (setf c (mod (* a c) m)))
+      (setf n (ash n -1))
+      (setf a (mod (* a a) m))
+      finally (return c)))