Data commit

Task/Modular-exponentiation/Jq/modular-exponentiation.jq

@@ -0,0 +1,29 @@
+# To take advantage of gojq's arbitrary-precision integer arithmetic:
+def power($b): . as $in | reduce range(0;$b) as $i (1; . * $in);
+
+# Returns (. ^ $exp) % $mod
+# where $exp >= 0, $mod != 0, and the input are integers.
+def modPow($exp; $mod):
+  if $mod == 0 then "Cannot take modPow with modulus 0." | error
+  elif $exp < 0 then "modPow with exp < 0 is not supported." | error
+  else . as $x
+  | {r: 1, base: ($x % $mod), exp: $exp}
+  | until( .exp <= 0 or .emit;
+         if .base == 0 then .emit = 0
+         else if .exp%2 == 1
+              then .r = (.r * .base) % $mod
+	      |    .exp |= (. - 1) / 2
+	      else .exp /= 2
+	      end
+         | .base |= (. * .) % $mod
+ 	 end )
+  | if .emit then .emit else .r end
+  end;
+
+def task:
+    2988348162058574136915891421498819466320163312926952423791023078876139 as $a
+  | 2351399303373464486466122544523690094744975233415544072992656881240319 as $b
+  | (10|power(40)) as $m
+  | $a | modPow($b; $m) ;
+
+task