A-M baby

Task/Modular-inverse/REXX/modular-inverse.rexx

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+/*REXX program calcuates the modular inverse of an integer  X  modulo Y.*/
+parse arg x y .                        /*get two integers from the C.L. */
+say  'modular inverse of '    x    " by "    y    ' ───► '     modInv(x,y)
+exit                                   /*stick a fork in it, we're done.*/
+/*──────────────────────────────────MODINV subroutine───────────────────*/
+modInv: parse arg a,b 1 ob;   ox=0;   $=1
+
+if b \= 1        then   do  while a>1
+                        parse value  a/b a//b b ox   with   q b a t
+                        ox=$-q*ox;   $=trunc(t)
+                        end    /*while a>1*/
+if $<0  then $=$+ob
+return $