Add constraint for Logup claimed cumsum (#830)

Add optional constraint for logup claimed sum
The constraint applies only in case that the claimed_sum is not the total sum
Uses for padding components with default rows

crates/prover/src/constraint_framework/logup.rs

@@ -21,13 +21,21 @@ use crate::core::poly::BitReversedOrder;
 use crate::core::utils::{bit_reverse_index, coset_index_to_circle_domain_index};
 use crate::core::ColumnVec;
 
+/// Represents the value of the prefix sum column at some index.
+/// Should be used to eliminate padded rows for the logup sum.
+pub type ClaimedPrefixSum = (SecureField, usize);
+
 /// Evaluates constraints for batched logups.
 /// These constraint enforce the sum of multiplicity_i / (z + sum_j alpha^j * x_j) = claimed_sum.
 pub struct LogupAtRow<E: EvalAtRow> {
     /// The index of the interaction used for the cumulative sum columns.
     pub interaction: usize,
     /// The total sum of all the fractions.
     pub total_sum: SecureField,
+    /// The claimed sum of the relevant fractions.
+    /// This is used for padding the component with default rows. Padding should be in bit-reverse.
+    /// None if the claimed_sum is the total_sum.
+    pub claimed_sum: Option<ClaimedPrefixSum>,
     /// The evaluation of the last cumulative sum column.
     pub prev_col_cumsum: E::EF,
     cur_frac: Option<Fraction<E::EF, E::EF>>,
@@ -37,10 +45,16 @@ pub struct LogupAtRow<E: EvalAtRow> {
     pub is_first: E::F,
 }
 impl<E: EvalAtRow> LogupAtRow<E> {
-    pub fn new(interaction: usize, total_sum: SecureField, is_first: E::F) -> Self {
+    pub fn new(
+        interaction: usize,
+        total_sum: SecureField,
+        claimed_sum: Option<ClaimedPrefixSum>,
+        is_first: E::F,
+    ) -> Self {
         Self {
             interaction,
             total_sum,
+            claimed_sum,
             prev_col_cumsum: E::EF::zero(),
             cur_frac: None,
             is_finalized: false,
@@ -64,9 +78,26 @@ impl<E: EvalAtRow> LogupAtRow<E> {
 
         let frac = self.cur_frac.unwrap();
 
-        let [cur_cumsum, prev_row_cumsum] =
-            eval.next_extension_interaction_mask(self.interaction, [0, -1]);
+        // TODO(ShaharS): remove `claimed_row_index` interaction value and get the shifted offset
+        // from the is_first column when constant columns are supported.
+        let (cur_cumsum, prev_row_cumsum) = match self.claimed_sum {
+            Some((claimed_sum, claimed_row_index)) => {
+                let [cur_cumsum, prev_row_cumsum, claimed_cumsum] = eval
+                    .next_extension_interaction_mask(
+                        self.interaction,
+                        [0, -1, claimed_row_index as isize],
+                    );
 
+                // Constrain that the claimed_sum in case that it is not equal to the total_sum.
+                eval.add_constraint((claimed_cumsum - claimed_sum) * self.is_first);
+                (cur_cumsum, prev_row_cumsum)
+            }
+            None => {
+                let [cur_cumsum, prev_row_cumsum] =
+                    eval.next_extension_interaction_mask(self.interaction, [0, -1]);
+                (cur_cumsum, prev_row_cumsum)
+            }
+        };
         // Fix `prev_row_cumsum` by subtracting `total_sum` if this is the first row.
         let fixed_prev_row_cumsum = prev_row_cumsum - self.is_first * self.total_sum;
         let diff = cur_cumsum - fixed_prev_row_cumsum - self.prev_col_cumsum;
@@ -277,7 +308,8 @@ mod tests {
     #[test]
     #[should_panic]
     fn test_logup_not_finalized_panic() {
-        let mut logup = LogupAtRow::<InfoEvaluator>::new(1, SecureField::one(), BaseField::one());
+        let mut logup =
+            LogupAtRow::<InfoEvaluator>::new(1, SecureField::one(), None, BaseField::one());
         logup.write_frac(
             &mut InfoEvaluator::default(),
             Fraction::new(SecureField::one(), SecureField::one()),

crates/prover/src/examples/blake/round/mod.rs

@@ -33,7 +33,7 @@ impl FrameworkEval for BlakeRoundEval {
             eval,
             xor_lookup_elements: &self.xor_lookup_elements,
             round_lookup_elements: &self.round_lookup_elements,
-            logup: LogupAtRow::new(1, self.total_sum, is_first),
+            logup: LogupAtRow::new(1, self.total_sum, None, is_first),
         };
         blake_eval.eval()
     }

crates/prover/src/examples/blake/scheduler/mod.rs

@@ -34,7 +34,7 @@ impl FrameworkEval for BlakeSchedulerEval {
             &mut eval,
             &self.blake_lookup_elements,
             &self.round_lookup_elements,
-            LogupAtRow::new(1, self.total_sum, is_first),
+            LogupAtRow::new(1, self.total_sum, None, is_first),
         );
         eval
     }

crates/prover/src/examples/blake/xor_table/mod.rs

@@ -107,7 +107,7 @@ impl<const ELEM_BITS: u32, const EXPAND_BITS: u32> FrameworkEval
         let xor_eval = constraints::XorTableEval::<'_, _, ELEM_BITS, EXPAND_BITS> {
             eval,
             lookup_elements: &self.lookup_elements,
-            logup: LogupAtRow::new(1, self.claimed_sum, is_first),
+            logup: LogupAtRow::new(1, self.claimed_sum, None, is_first),
         };
         xor_eval.eval()
     }

crates/prover/src/examples/plonk/mod.rs

@@ -3,7 +3,9 @@ use num_traits::One;
 use tracing::{span, Level};
 
 use crate::constraint_framework::constant_columns::gen_is_first;
-use crate::constraint_framework::logup::{LogupAtRow, LogupTraceGenerator, LookupElements};
+use crate::constraint_framework::logup::{
+    ClaimedPrefixSum, LogupAtRow, LogupTraceGenerator, LookupElements,
+};
 use crate::constraint_framework::{
     assert_constraints, EvalAtRow, FrameworkComponent, FrameworkEval, TraceLocationAllocator,
 };
@@ -29,6 +31,7 @@ pub type PlonkComponent = FrameworkComponent<PlonkEval>;
 pub struct PlonkEval {
     pub log_n_rows: u32,
     pub lookup_elements: LookupElements<2>,
+    pub claimed_sum: ClaimedPrefixSum,
     pub total_sum: SecureField,
     pub base_trace_location: TreeSubspan,
     pub interaction_trace_location: TreeSubspan,
@@ -46,7 +49,7 @@ impl FrameworkEval for PlonkEval {
 
     fn evaluate<E: EvalAtRow>(&self, mut eval: E) -> E {
         let [is_first] = eval.next_interaction_mask(2, [0]);
-        let mut logup = LogupAtRow::<_>::new(1, self.total_sum, is_first);
+        let mut logup = LogupAtRow::<_>::new(1, self.total_sum, Some(self.claimed_sum), is_first);
 
         let [a_wire] = eval.next_interaction_mask(2, [0]);
         let [b_wire] = eval.next_interaction_mask(2, [0]);
@@ -113,11 +116,12 @@ pub fn gen_trace(
 
 pub fn gen_interaction_trace(
     log_size: u32,
+    padding_offset: usize,
     circuit: &PlonkCircuitTrace,
     lookup_elements: &LookupElements<2>,
 ) -> (
     ColumnVec<CircleEvaluation<SimdBackend, BaseField, BitReversedOrder>>,
-    SecureField,
+    [SecureField; 2],
 ) {
     let _span = span!(Level::INFO, "Generate interaction trace").entered();
     let mut logup_gen = LogupTraceGenerator::new(log_size);
@@ -141,7 +145,7 @@ pub fn gen_interaction_trace(
     }
     col_gen.finalize_col();
 
-    logup_gen.finalize_last()
+    logup_gen.finalize_at([(1 << log_size) - 1, padding_offset])
 }
 
 #[allow(unused)]
@@ -156,6 +160,7 @@ pub fn prove_fibonacci_plonk(
     for _ in 0..(1 << log_n_rows) {
         fib_values.push(fib_values[fib_values.len() - 1] + fib_values[fib_values.len() - 2]);
     }
+    let padding_offset = 17;
     let range = 0..(1 << log_n_rows);
     let mut circuit = PlonkCircuitTrace {
         mult: range.clone().map(|_| 2.into()).collect(),
@@ -197,7 +202,8 @@ pub fn prove_fibonacci_plonk(
 
     // Interaction trace.
     let span = span!(Level::INFO, "Interaction").entered();
-    let (trace, total_sum) = gen_interaction_trace(log_n_rows, &circuit, &lookup_elements);
+    let (trace, [total_sum, claimed_sum]) =
+        gen_interaction_trace(log_n_rows, padding_offset, &circuit, &lookup_elements);
     let mut tree_builder = commitment_scheme.tree_builder();
     let interaction_trace_location = tree_builder.extend_evals(trace);
     tree_builder.commit(channel);
@@ -227,6 +233,7 @@ pub fn prove_fibonacci_plonk(
         PlonkEval {
             log_n_rows,
             lookup_elements,
+            claimed_sum: (claimed_sum, padding_offset),
             total_sum,
             base_trace_location,
             interaction_trace_location,

crates/prover/src/examples/poseidon/mod.rs

@@ -61,7 +61,7 @@ impl FrameworkEval for PoseidonEval {
     }
     fn evaluate<E: EvalAtRow>(&self, mut eval: E) -> E {
         let [is_first] = eval.next_interaction_mask(2, [0]);
-        let logup = LogupAtRow::new(1, self.total_sum, is_first);
+        let logup = LogupAtRow::new(1, self.total_sum, None, is_first);
         eval_poseidon_constraints(&mut eval, logup, &self.lookup_elements);
         eval
     }
@@ -482,7 +482,7 @@ mod tests {
             let [is_first] = eval.next_interaction_mask(2, [0]);
             eval_poseidon_constraints(
                 &mut eval,
-                LogupAtRow::new(1, total_sum, is_first),
+                LogupAtRow::new(1, total_sum, None, is_first),
                 &lookup_elements,
             );
         });