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Task/Modular-inverse/EchoLisp/modular-inverse.echolisp

@@ -0,0 +1,10 @@
+(lib 'math) ;; for egcd = extended gcd
+
+(define (mod-inv x m)
+    (define-values (g inv q) (egcd x m))
+    (unless (= 1 g) (error 'not-coprimes (list x m) ))
+    (if (< inv 0) (+ m inv) inv))
+
+(mod-inv 42 2017)  → 1969
+(mod-inv 42 666)
+🔴 error: not-coprimes (42 666)