1/* Xor3 function for sha256
 2
 3out = a ^ b ^ c  =>
 4
 5out = a+b+c - 2*a*b - 2*a*c - 2*b*c + 4*a*b*c   =>
 6
 7out = a*( 1 - 2*b - 2*c + 4*b*c ) + b + c - 2*b*c =>
 8
 9mid = b*c
10out = a*( 1 - 2*b -2*c + 4*mid ) + b + c - 2 * mid
11
12*/
13
14template Xor3(n) {
15    signal input a[n];
16    signal input b[n];
17    signal input c[n];
18    signal output out[n];
19    signal mid[n];
20
21    for (var k=0; k<n; k++) {
22        mid[k] <== b[k]*c[k];
23        out[k] <== a[k] * (1 -2*b[k]  -2*c[k] +4*mid[k]) + b[k] + c[k] -2*mid[k];
24    }
25}