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4f873e6205
Related to the issue of implementing basic bus (#1497), I have implemented basic bus together with an example (`permutation_via_bus.asm`) as specified inside the issue. Currently, `test_data/std/bus_permutation_via_challenges.asm` works as intended (To make it sound, stage(1) witness columns need to be exposed publicly and verifier needs to check such as `out_z1 + out_z2 = 0`) We can now check using RUST_LOG=trace and adding the final z1 and z2 is equal to 0. However, `test_data/std/bus_permutation_via_challenges_ext.asm` is not working correctly as intended. This will be fixed with the following commits.
104 lines
4.5 KiB
Rust
104 lines
4.5 KiB
Rust
use std::check::assert;
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use std::check::panic;
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use std::math::fp2::Fp2;
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use std::math::fp2::add_ext;
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use std::math::fp2::sub_ext;
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use std::math::fp2::mul_ext;
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use std::math::fp2::inv_ext;
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use std::math::fp2::eval_ext;
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use std::math::fp2::unpack_ext;
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use std::math::fp2::unpack_ext_array;
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use std::math::fp2::next_ext;
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use std::math::fp2::from_base;
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use std::math::fp2::needs_extension;
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use std::math::fp2::is_extension;
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use std::math::fp2::fp2_from_array;
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use std::math::fp2::constrain_eq_ext;
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use std::protocols::fingerprint::fingerprint_with_id;
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use std::prover::eval;
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/// Sends the tuple (id, tuple...) to the bus by adding
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/// `multiplicity / (beta - fingerprint(id, tuple...))` to `acc`
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/// It is the callers responsibility to properly constrain the multiplicity (e.g. constrain
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/// it to be boolean) if needed.
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///
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/// # Arguments:
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///
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/// - is_first: A column that is 1 for the first row and 0 for the rest
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/// - id: Interaction Id
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/// - tuple: An array of columns to be sent to the bus
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/// - multiplicity: The multiplicity which shows how many times a column will be sent
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/// - acc: A phase-2 witness column to be used as the accumulator. If 2 are provided, computations
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/// are done on the F_{p^2} extension field.
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/// - alpha: A challenge used to compress id and tuple
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/// - beta: A challenge used to update the accumulator
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///
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/// # Returns:
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///
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/// - Constraints to be added to enforce the bus
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let bus_interaction: expr, expr, expr[], expr, expr[], Fp2<expr>, Fp2<expr> -> Constr[] = |is_first, id, tuple, multiplicity, acc, alpha, beta| {
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// Implemented as: folded = (beta - fingerprint(id, tuple...));
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let folded = sub_ext(beta, fingerprint_with_id(id, tuple, alpha));
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let folded_next = next_ext(folded);
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let m_ext = from_base(multiplicity);
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let m_ext_next = next_ext(m_ext);
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let acc_ext = fp2_from_array(acc);
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let next_acc = next_ext(acc_ext);
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let is_first_next = from_base(is_first');
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// Update rule:
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// acc' = acc * (1 - is_first') + multiplicity' / folded'
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// or equivalently:
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// folded' * (acc' - acc * (1 - is_first')) - multiplicity' = 0
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let update_expr = sub_ext(
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mul_ext(folded_next, sub_ext(next_acc, mul_ext(acc_ext, sub_ext(from_base(1), is_first_next)))), m_ext_next
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);
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constrain_eq_ext(update_expr, from_base(0))
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};
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/// Compute acc' = acc * (1 - is_first') + multiplicity' / fingerprint_with_id(id, (a1', a2')),
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/// using extension field arithmetic.
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/// This is intended to be used as a hint in the extension field case; for the base case
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/// automatic witgen is smart enough to figure out the value of the accumulator.
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let compute_next_z_send: expr, expr, expr[], expr, Fp2<expr>, Fp2<expr>, Fp2<expr> -> fe[] = query |is_first, id, tuple, multiplicity, acc, alpha, beta| {
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// Implemented as: folded = (beta - fingerprint(id, tuple...));
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// `multiplicity / (beta - fingerprint(id, tuple...))` to `acc`
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let folded = sub_ext(beta, fingerprint_with_id(id, tuple, alpha));
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let folded_next = next_ext(folded);
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let m_ext = from_base(multiplicity);
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let m_ext_next = next_ext(m_ext);
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let is_first_next = eval(is_first');
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let current_acc = if is_first_next == 1 {from_base(0)} else {eval_ext(acc)};
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// acc' = acc * (1 - is_first') + multiplicity / fingerprint_with_id(id, (a1', a2'))
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let res = add_ext(
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current_acc,
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mul_ext(eval_ext(m_ext_next), inv_ext(eval_ext(folded_next)))
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);
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unpack_ext_array(res)
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};
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/// Compute acc' = acc * (1 - is_first') - multiplicity' / fingerprint_with_id(id, (a1', a2')),
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/// using extension field arithmetic.
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/// This is intended to be used as a hint in the extension field case; for the base case
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/// automatic witgen is smart enough to figure out the value of the accumulator.
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let compute_next_z_receive: expr, expr, expr[], expr, Fp2<expr>, Fp2<expr>, Fp2<expr> -> fe[] = query |is_first, id, tuple, multiplicity, acc, alpha, beta|
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compute_next_z_send(is_first, id, tuple, -multiplicity, acc, alpha, beta);
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/// Convenience function for bus interaction to send columns
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let bus_send: expr, expr, expr[], expr, expr[], Fp2<expr>, Fp2<expr> -> Constr[] = |is_first, id, tuple, multiplicity, acc, alpha, beta| {
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bus_interaction(is_first, id, tuple, multiplicity, acc, alpha, beta)
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};
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/// Convenience function for bus interaction to receive columns
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let bus_receive: expr, expr, expr[], expr, expr[], Fp2<expr>, Fp2<expr> -> Constr[] = |is_first, id, tuple, multiplicity, acc, alpha, beta| {
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bus_interaction(is_first, id, tuple, -1 * multiplicity, acc, alpha, beta)
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}; |