digest_selector_gadget.tcc

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/**
 *****************************************************************************
 * @author     This file is part of libsnark, developed by SCIPR Lab
 *             and contributors (see AUTHORS).
 * @copyright  MIT license (see LICENSE file)
 *****************************************************************************/
#ifndef DIGEST_SELECTOR_GADGET_TCC_
#define DIGEST_SELECTOR_GADGET_TCC_
 
namespace libsnark
{
 
template<typename FieldT>
digest_selector_gadget<FieldT>::digest_selector_gadget(
    protoboard<FieldT> &pb,
    const size_t digest_size,
    const digest_variable<FieldT> &input,
    const pb_linear_combination<FieldT> &is_right,
    const digest_variable<FieldT> &left,
    const digest_variable<FieldT> &right,
    const std::string &annotation_prefix)
    : gadget<FieldT>(pb, annotation_prefix)
    , digest_size(digest_size)
    , input(input)
    , is_right(is_right)
    , left(left)
    , right(right)
{
}
 
template<typename FieldT>
void digest_selector_gadget<FieldT>::generate_r1cs_constraints()
{
    for (size_t i = 0; i < digest_size; ++i) {
        /*
          input = is_right * right + (1-is_right) * left
          input - left = is_right(right - left)
        */
        this->pb.add_r1cs_constraint(
            r1cs_constraint<FieldT>(
                is_right,
                right.bits[i] - left.bits[i],
                input.bits[i] - left.bits[i]),
            FMT(this->annotation_prefix, " propagate_%zu", i));
    }
}
 
template<typename FieldT>
void digest_selector_gadget<FieldT>::generate_r1cs_witness()
{
    is_right.evaluate(this->pb);
 
    assert(
        this->pb.lc_val(is_right) == FieldT::one() ||
        this->pb.lc_val(is_right) == FieldT::zero());
    if (this->pb.lc_val(is_right) == FieldT::one()) {
        for (size_t i = 0; i < digest_size; ++i) {
            this->pb.val(right.bits[i]) = this->pb.val(input.bits[i]);
        }
    } else {
        for (size_t i = 0; i < digest_size; ++i) {
            this->pb.val(left.bits[i]) = this->pb.val(input.bits[i]);
        }
    }
}
 
} // namespace libsnark
 
#endif // DIGEST_SELECTOR_GADGET_TCC_