archive-monorepo/@tornado/circomlib/circuits/bitify.circom

/*
    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/>.
*/

include "comparators.circom";
include "aliascheck.circom";


/* This doesn't check aliasing, so for n > 253 there are multiple bit strings for each number */
template Num2Bits(n) {
    signal input in;
    signal output out[n];
    var lc1=0;

    for (var i = 0; i<n; i++) {
        out[i] <-- (in >> i) & 1;
        out[i] * (out[i] -1 ) === 0;
        lc1 += out[i] * 2**i;
    }

    lc1 === in;
}

template Num2Bits_strict() {
    signal input in;
    signal output out[254];

    component aliasCheck = AliasCheck();
    component n2b = Num2Bits(254);
    in ==> n2b.in;

    for (var i=0; i<254; i++) {
        n2b.out[i] ==> out[i];
        n2b.out[i] ==> aliasCheck.in[i];
    }
}

template Bits2Num(n) {
    signal input in[n];
    signal output out;
    var lc1=0;

    for (var i = 0; i<n; i++) {
        lc1 += in[i] * 2**i;
    }

    lc1 ==> out;
}

template Bits2Num_strict() {
    signal input in[n];
    signal output out;

    component aliasCheck = AliasCheck();
    component b2n = Bits2Num(254);

    for (var i=0; i<254; i++) {
        in[i] ==> b2n.in[i];
        in[i] ==> aliasCheck.in[i];
    }

    b2n.out ==> out;
}

/* n must not exceed 253 */  
template Num2BitsNeg(n) {
    signal input in;
    signal output out[n];
    var lc1=0;

    component isZero;

    isZero = IsZero();

    var neg = n == 0 ? 0 : 2**n - in;

    for (var i = 0; i<n; i++) {
        out[i] <-- (neg >> i) & 1;
        out[i] * (out[i] -1 ) === 0;
        lc1 += out[i] * 2**i;
    }

    in ==> isZero.in;



    lc1 + isZero.out * 2**n === 2**n - in;
}