feat: initial implementation of LogUp-GKR bus

Co-authored-by: Al-Kindi-0 <[email protected]>
Co-authored-by: Philippe Laferrière <[email protected]>

air/src/trace/main_trace.rs

@@ -19,9 +19,6 @@ use super::{
 use core::ops::{Deref, Range};
 use vm_core::{utils::range, Felt, Word, ONE, ZERO};
 
-#[cfg(any(test, feature = "internals"))]
-use alloc::vec::Vec;
-
 // CONSTANTS
 // ================================================================================================
 
@@ -43,6 +40,13 @@ impl Deref for MainTrace {
     }
 }
 
+#[cfg(any(test, feature = "internals"))]
+impl core::ops::DerefMut for MainTrace {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.columns
+    }
+}
+
 impl MainTrace {
     pub fn new(main_trace: ColMatrix<Felt>) -> Self {
         Self {
@@ -55,7 +59,7 @@ impl MainTrace {
     }
 
     #[cfg(any(test, feature = "internals"))]
-    pub fn get_column_range(&self, range: Range<usize>) -> Vec<Vec<Felt>> {
+    pub fn get_column_range(&self, range: Range<usize>) -> alloc::vec::Vec<alloc::vec::Vec<Felt>> {
         range.fold(vec![], |mut acc, col_idx| {
             acc.push(self.get_column(col_idx).to_vec());
             acc

processor/Cargo.toml

@@ -26,8 +26,10 @@ std = ["vm-core/std", "winter-prover/std"]
 tracing = { version = "0.1", default-features = false, features = [
     "attributes",
 ] }
-vm-core = { package = "miden-core", path = "../core", version = "0.9", default-features = false }
 miden-air = { package = "miden-air", path = "../air", version = "0.9", default-features = false }
+static_assertions = "1.1.0"
+thiserror = { version = "1.0", default-features = false }
+vm-core = { package = "miden-core", path = "../core", version = "0.9", default-features = false }
 winter-prover = { package = "winter-prover", version = "0.9", default-features = false }
 
 [dev-dependencies]

processor/src/lib.rs

@@ -61,7 +61,10 @@ use chiplets::Chiplets;
 
 mod trace;
 use trace::TraceFragment;
-pub use trace::{ChipletsLengths, ExecutionTrace, TraceLenSummary, NUM_RAND_ROWS};
+pub use trace::{
+    prove_virtual_bus, verify_virtual_bus, ChipletsLengths, ExecutionTrace, TraceLenSummary,
+    NUM_RAND_ROWS,
+};
 
 mod errors;
 pub use errors::{ExecutionError, Ext2InttError};

processor/src/trace/mod.rs

@@ -18,6 +18,9 @@ use winter_prover::{crypto::RandomCoin, EvaluationFrame, Trace, TraceInfo};
 mod utils;
 pub use utils::{AuxColumnBuilder, ChipletsLengths, TraceFragment, TraceLenSummary};
 
+mod virtual_bus;
+pub use virtual_bus::{prove as prove_virtual_bus, verify as verify_virtual_bus};
+
 #[cfg(test)]
 mod tests;
 #[cfg(test)]

processor/src/trace/virtual_bus/circuit/error.rs

@@ -0,0 +1,24 @@
+use crate::trace::virtual_bus::sum_check::SumCheckProverError;
+use crate::trace::virtual_bus::sum_check::SumCheckVerifierError;
+
+#[derive(Debug, thiserror::Error)]
+pub enum ProverError {
+    #[error("failed to generate multi-linear from the given evaluations")]
+    FailedToGenerateML,
+    #[error("failed to generate the sum-check proof")]
+    FailedToProveSumCheck(#[from] SumCheckProverError),
+    #[error("failed to generate the random challenge")]
+    FailedToGenerateChallenge,
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum VerifierError {
+    #[error("one of the claimed circuit denominators is zero")]
+    ZeroOutputDenominator,
+    #[error("the output of the fraction circuit is not equal to the expected value")]
+    MismatchingCircuitOutput,
+    #[error("failed to generate the random challenge")]
+    FailedToGenerateChallenge,
+    #[error("failed to verify the sum-check proof")]
+    FailedToVerifySumCheck(#[from] SumCheckVerifierError),
+}

processor/src/trace/virtual_bus/circuit/mod.rs

@@ -0,0 +1,290 @@
+use core::ops::Add;
+
+use crate::trace::virtual_bus::multilinear::EqFunction;
+use crate::trace::virtual_bus::sum_check::{CompositionPolynomial, RoundProof};
+use alloc::vec::Vec;
+use miden_air::trace::chiplets::{MEMORY_D0_COL_IDX, MEMORY_D1_COL_IDX};
+use miden_air::trace::decoder::{DECODER_OP_BITS_OFFSET, DECODER_USER_OP_HELPERS_OFFSET};
+use miden_air::trace::range::{M_COL_IDX, V_COL_IDX};
+use miden_air::trace::{CHIPLETS_OFFSET, TRACE_WIDTH};
+use prover::CircuitLayerPolys;
+use static_assertions::const_assert;
+use vm_core::{Felt, FieldElement};
+
+mod error;
+mod prover;
+pub use prover::prove;
+
+mod verifier;
+pub use verifier::verify;
+
+use super::multilinear::MultiLinearPoly;
+use super::sum_check::{FinalOpeningClaim, Proof as SumCheckProof};
+
+/// Defines the number of wires in the input layer that are generated from a single main trace row.
+const NUM_WIRES_PER_TRACE_ROW: usize = 8;
+const_assert!(NUM_WIRES_PER_TRACE_ROW.is_power_of_two());
+
+// CIRCUIT WIRE
+// ================================================================================================
+
+/// Represents a fraction `numerator / denominator` as a pair `(numerator, denominator)`. This is
+/// the type for the gates' inputs in [`prover::EvaluatedCircuit`].
+///
+/// Hence, addition is defined in the natural way fractions are added together: `a/b + c/d = (ad +
+/// bc) / bd`.
+#[derive(Debug, Clone, Copy)]
+pub struct CircuitWire<E: FieldElement> {
+    numerator: E,
+    denominator: E,
+}
+
+impl<E> CircuitWire<E>
+where
+    E: FieldElement,
+{
+    /// Creates new projective coordinates from a numerator and a denominator.
+    pub fn new(numerator: E, denominator: E) -> Self {
+        assert_ne!(denominator, E::ZERO);
+
+        Self {
+            numerator,
+            denominator,
+        }
+    }
+}
+
+impl<E> Add for CircuitWire<E>
+where
+    E: FieldElement,
+{
+    type Output = Self;
+
+    fn add(self, other: Self) -> Self {
+        let numerator = self.numerator * other.denominator + other.numerator * self.denominator;
+        let denominator = self.denominator * other.denominator;
+
+        Self::new(numerator, denominator)
+    }
+}
+
+/// Converts a main trace row (or more generally "query") to numerators and denominators of the
+/// input layer.
+fn evaluate_fractions_at_main_trace_query<E>(
+    query: &[E],
+    log_up_randomness: &[E],
+) -> [[E; NUM_WIRES_PER_TRACE_ROW]; 2]
+where
+    E: FieldElement,
+{
+    // numerators
+    let multiplicity = query[M_COL_IDX];
+    let f_m = {
+        let mem_selec0 = query[CHIPLETS_OFFSET];
+        let mem_selec1 = query[CHIPLETS_OFFSET + 1];
+        let mem_selec2 = query[CHIPLETS_OFFSET + 2];
+        mem_selec0 * mem_selec1 * (E::ONE - mem_selec2)
+    };
+
+    let f_rc = {
+        let op_bit_4 = query[DECODER_OP_BITS_OFFSET + 4];
+        let op_bit_5 = query[DECODER_OP_BITS_OFFSET + 5];
+        let op_bit_6 = query[DECODER_OP_BITS_OFFSET + 6];
+
+        (E::ONE - op_bit_4) * (E::ONE - op_bit_5) * op_bit_6
+    };
+
+    // denominators
+    let alphas = log_up_randomness;
+
+    let table_denom = alphas[0] - query[V_COL_IDX];
+    let memory_denom_0 = -(alphas[0] - query[MEMORY_D0_COL_IDX]);
+    let memory_denom_1 = -(alphas[0] - query[MEMORY_D1_COL_IDX]);
+    let stack_value_denom_0 = -(alphas[0] - query[DECODER_USER_OP_HELPERS_OFFSET]);
+    let stack_value_denom_1 = -(alphas[0] - query[DECODER_USER_OP_HELPERS_OFFSET + 1]);
+    let stack_value_denom_2 = -(alphas[0] - query[DECODER_USER_OP_HELPERS_OFFSET + 2]);
+    let stack_value_denom_3 = -(alphas[0] - query[DECODER_USER_OP_HELPERS_OFFSET + 3]);
+
+    [
+        [multiplicity, f_m, f_m, f_rc, f_rc, f_rc, f_rc, E::ZERO],
+        [
+            table_denom,
+            memory_denom_0,
+            memory_denom_1,
+            stack_value_denom_0,
+            stack_value_denom_1,
+            stack_value_denom_2,
+            stack_value_denom_3,
+            E::ONE,
+        ],
+    ]
+}
+
+/// Computes the wires added to the input layer that come from a given main trace row (or more
+/// generally, "query").
+fn compute_input_layer_wires_at_main_trace_query<E>(
+    query: &[E],
+    log_up_randomness: &[E],
+) -> [CircuitWire<E>; NUM_WIRES_PER_TRACE_ROW]
+where
+    E: FieldElement,
+{
+    let [numerators, denominators] =
+        evaluate_fractions_at_main_trace_query(query, log_up_randomness);
+    let input_gates_values: Vec<CircuitWire<E>> = numerators
+        .into_iter()
+        .zip(denominators)
+        .map(|(numerator, denominator)| CircuitWire::new(numerator, denominator))
+        .collect();
+    input_gates_values.try_into().unwrap()
+}
+
+/// A GKR proof for the correct evaluation of the sum of fractions circuit.
+#[derive(Debug)]
+pub struct GkrCircuitProof<E: FieldElement> {
+    circuit_outputs: CircuitLayerPolys<E>,
+    before_final_layer_proofs: BeforeFinalLayerProof<E>,
+    final_layer_proof: FinalLayerProof<E>,
+}
+
+impl<E: FieldElement> GkrCircuitProof<E> {
+    pub fn get_final_opening_claim(&self) -> FinalOpeningClaim<E> {
+        self.final_layer_proof.after_merge_proof.openings_claim.clone()
+    }
+}
+
+/// A set of sum-check proofs for all GKR layers but for the input circuit layer.
+#[derive(Debug)]
+pub struct BeforeFinalLayerProof<E: FieldElement> {
+    pub proof: Vec<SumCheckProof<E>>,
+}
+
+/// A proof for the input circuit layer i.e., the final layer in the GKR protocol.
+#[derive(Debug)]
+pub struct FinalLayerProof<E: FieldElement> {
+    before_merge_proof: Vec<RoundProof<E>>,
+    after_merge_proof: SumCheckProof<E>,
+}
+
+/// Represents a claim to be proven by a subsequent call to the sum-check protocol.
+#[derive(Debug)]
+pub struct GkrClaim<E: FieldElement> {
+    pub evaluation_point: Vec<E>,
+    pub claimed_evaluation: (E, E),
+}
+
+/// A composition polynomial used in the GKR protocol for all of its sum-checks except the final
+/// one.
+#[derive(Clone)]
+pub struct GkrComposition<E>
+where
+    E: FieldElement<BaseField = Felt>,
+{
+    pub combining_randomness: E,
+}
+
+impl<E> GkrComposition<E>
+where
+    E: FieldElement<BaseField = Felt>,
+{
+    pub fn new(combining_randomness: E) -> Self {
+        Self {
+            combining_randomness,
+        }
+    }
+}
+
+impl<E> CompositionPolynomial<E> for GkrComposition<E>
+where
+    E: FieldElement<BaseField = Felt>,
+{
+    fn max_degree(&self) -> u32 {
+        3
+    }
+
+    fn evaluate(&self, query: &[E]) -> E {
+        let eval_left_numerator = query[0];
+        let eval_right_numerator = query[1];
+        let eval_left_denominator = query[2];
+        let eval_right_denominator = query[3];
+        let eq_eval = query[4];
+        eq_eval
+            * ((eval_left_numerator * eval_right_denominator
+                + eval_right_numerator * eval_left_denominator)
+                + eval_left_denominator * eval_right_denominator * self.combining_randomness)
+    }
+}
+
+/// A composition polynomial used in the GKR protocol for its final sum-check.
+#[derive(Clone)]
+pub struct GkrCompositionMerge<E>
+where
+    E: FieldElement<BaseField = Felt>,
+{
+    pub sum_check_combining_randomness: E,
+    pub tensored_merge_randomness: Vec<E>,
+    pub log_up_randomness: Vec<E>,
+}
+
+impl<E> GkrCompositionMerge<E>
+where
+    E: FieldElement<BaseField = Felt>,
+{
+    pub fn new(
+        combining_randomness: E,
+        merge_randomness: Vec<E>,
+        log_up_randomness: Vec<E>,
+    ) -> Self {
+        let tensored_merge_randomness =
+            EqFunction::ml_at(merge_randomness.clone()).evaluations().to_vec();
+
+        Self {
+            sum_check_combining_randomness: combining_randomness,
+            tensored_merge_randomness,
+            log_up_randomness,
+        }
+    }
+}
+
+impl<E> CompositionPolynomial<E> for GkrCompositionMerge<E>
+where
+    E: FieldElement<BaseField = Felt>,
+{
+    fn max_degree(&self) -> u32 {
+        // Computed as:
+        // 1 + max(left_numerator_degree + right_denom_degree, right_numerator_degree +
+        // left_denom_degree)
+        5
+    }
+
+    fn evaluate(&self, query: &[E]) -> E {
+        let [numerators, denominators] =
+            evaluate_fractions_at_main_trace_query(query, &self.log_up_randomness);
+
+        let numerators = MultiLinearPoly::from_evaluations(numerators.to_vec()).unwrap();
+        let denominators = MultiLinearPoly::from_evaluations(denominators.to_vec()).unwrap();
+
+        let (left_numerators, right_numerators) = numerators.project_least_significant_variable();
+        let (left_denominators, right_denominators) =
+            denominators.project_least_significant_variable();
+
+        let eval_left_numerators =
+            left_numerators.evaluate_with_lagrange_kernel(&self.tensored_merge_randomness);
+        let eval_right_numerators =
+            right_numerators.evaluate_with_lagrange_kernel(&self.tensored_merge_randomness);
+
+        let eval_left_denominators =
+            left_denominators.evaluate_with_lagrange_kernel(&self.tensored_merge_randomness);
+        let eval_right_denominators =
+            right_denominators.evaluate_with_lagrange_kernel(&self.tensored_merge_randomness);
+
+        let eq_eval = query[TRACE_WIDTH];
+
+        eq_eval
+            * ((eval_left_numerators * eval_right_denominators
+                + eval_right_numerators * eval_left_denominators)
+                + eval_left_denominators
+                    * eval_right_denominators
+                    * self.sum_check_combining_randomness)
+    }
+}