Merge other basic circuits here

circuits/sha256/xor3.circom

@@ -0,0 +1,44 @@
+/*
+    Copyright 2018 0KIMS association.
+
+    This file is part of circom (Zero Knowledge Circuit Compiler).
+
+    circom is a free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    circom is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+    or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
+    License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with circom. If not, see <https://www.gnu.org/licenses/>.
+*/
+
+/* Xor3 function for sha256
+
+out = a ^ b ^ c  =>
+
+out = a+b+c - 2*a*b - 2*a*c - 2*b*c + 4*a*b*c   =>
+
+out = a*( 1 - 2*b - 2*c + 4*b*c ) + b + c - 2*b*c =>
+
+mid = b*c
+out = a*( 1 - 2*b -2*c + 4*mid ) + b + c - 2 * mid
+
+*/
+
+template Xor3(n) {
+    signal input a[n];
+    signal input b[n];
+    signal input c[n];
+    signal output out[n];
+    signal mid[n];
+
+    for (var k=0; k<n; k++) {
+        mid[k] <== b[k]*c[k];
+        out[k] <== a[k] * (1 -2*b[k]  -2*c[k] +4*mid[k]) + b[k] + c[k] -2*mid[k];
+    }
+}