circomlib/circuits/compconstant.circom
2018-12-06 17:32:49 +01:00

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include "bitify.circom";
// Returns 1 if in (in binary) > ct
template CompConstant(ct) {
signal input in[254];
signal output out;
signal parts[127];
signal sout;
var clsb;
var cmsb;
var slsb;
var smsb;
var sum=0;
var b = (1 << 128) -1;
var a = 1;
var e = 1;
var i;
for (i=0;i<127; i++) {
clsb = (ct >> (i*2)) & 1;
cmsb = (ct >> (i*2+1)) & 1;
slsb = in[i*2];
smsb = in[i*2+1];
if ((cmsb==0)&(clsb==0)) {
parts[i] <== -b*smsb*slsb + b*smsb + b*slsb;
} else if ((cmsb==0)&(clsb==1)) {
parts[i] <== a*smsb*slsb - a*slsb + b*smsb - a*smsb + a;
} else if ((cmsb==1)&(clsb==0)) {
parts[i] <== b*smsb*slsb - a*smsb + a;
} else {
parts[i] <== -a*smsb*slsb + a;
}
sum = sum + parts[i];
b = b -e;
a = a +e;
e = e*2;
}
sout <== sum;
component num2bits = Num2Bits(135);
num2bits.in <== sout;
out <== num2bits.out[127];
}