feat!: add MultiplyExpr (#18)

crates/proof-of-sql/src/base/database/column.rs

@@ -131,6 +131,23 @@ impl<'a, S: Scalar> Column<'a, S> {
         }
     }
 
+    /// Returns element at index as scalar
+    ///
+    /// Note that if index is out of bounds, this function will return None
+    pub(crate) fn scalar_at(&self, index: usize) -> Option<S> {
+        (index < self.len()).then_some(match self {
+            Self::Boolean(col) => S::from(col[index]),
+            Self::SmallInt(col) => S::from(col[index]),
+            Self::Int(col) => S::from(col[index]),
+            Self::BigInt(col) => S::from(col[index]),
+            Self::Int128(col) => S::from(col[index]),
+            Self::Scalar(col) => col[index],
+            Self::Decimal75(_, _, col) => col[index],
+            Self::VarChar((_, scals)) => scals[index],
+            Self::TimestampTZ(_, _, col) => S::from(col[index]),
+        })
+    }
+
     /// Convert a column to a vector of Scalar values with scaling
     pub(crate) fn to_scalar_with_scaling(&self, scale: i8) -> Vec<S> {
         let scale_factor = scale_scalar(S::ONE, scale).expect("Invalid scale factor");

crates/proof-of-sql/src/base/math/decimal.rs

@@ -30,6 +30,11 @@ pub enum DecimalError {
     /// or non-positive aka InvalidPrecision
     InvalidPrecision(String),
 
+    #[error("Decimal scale is not valid: {0}")]
+    /// Decimal scale is not valid. Here we use i16 in order to include
+    /// invalid scale values
+    InvalidScale(i16),
+
     #[error("Unsupported operation: cannot round decimal: {0}")]
     /// This error occurs when attempting to scale a
     /// decimal in such a way that a loss of precision occurs.

crates/proof-of-sql/src/sql/ast/mod.rs

@@ -7,6 +7,11 @@ pub(crate) use add_subtract_expr::AddSubtractExpr;
 #[cfg(all(test, feature = "blitzar"))]
 mod add_subtract_expr_test;
 
+mod multiply_expr;
+use multiply_expr::MultiplyExpr;
+#[cfg(all(test, feature = "blitzar"))]
+mod multiply_expr_test;
+
 mod filter_expr;
 pub(crate) use filter_expr::FilterExpr;
 #[cfg(test)]
@@ -59,7 +64,8 @@ pub(crate) use comparison_util::scale_and_subtract;
 
 mod numerical_util;
 pub(crate) use numerical_util::{
-    add_subtract_columns, scale_and_add_subtract_eval, try_add_subtract_column_types,
+    add_subtract_columns, multiply_columns, scale_and_add_subtract_eval,
+    try_add_subtract_column_types, try_multiply_column_types,
 };
 
 mod equals_expr;

crates/proof-of-sql/src/sql/ast/multiply_expr.rs

@@ -0,0 +1,116 @@
+use super::{ProvableExpr, ProvableExprPlan};
+use crate::{
+    base::{
+        commitment::Commitment,
+        database::{Column, ColumnRef, ColumnType, CommitmentAccessor, DataAccessor},
+        proof::ProofError,
+    },
+    sql::{
+        ast::{multiply_columns, try_multiply_column_types},
+        proof::{CountBuilder, ProofBuilder, SumcheckSubpolynomialType, VerificationBuilder},
+    },
+};
+use bumpalo::Bump;
+use num_traits::One;
+use serde::{Deserialize, Serialize};
+use std::collections::HashSet;
+
+/// Provable numerical * expression
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub struct MultiplyExpr<C: Commitment> {
+    lhs: Box<ProvableExprPlan<C>>,
+    rhs: Box<ProvableExprPlan<C>>,
+}
+
+impl<C: Commitment> MultiplyExpr<C> {
+    /// Create numerical `*` expression
+    pub fn new(lhs: Box<ProvableExprPlan<C>>, rhs: Box<ProvableExprPlan<C>>) -> Self {
+        Self { lhs, rhs }
+    }
+}
+
+impl<C: Commitment> ProvableExpr<C> for MultiplyExpr<C> {
+    fn count(&self, builder: &mut CountBuilder) -> Result<(), ProofError> {
+        self.lhs.count(builder)?;
+        self.rhs.count(builder)?;
+        builder.count_subpolynomials(1);
+        builder.count_intermediate_mles(1);
+        builder.count_degree(3);
+        Ok(())
+    }
+
+    fn data_type(&self) -> ColumnType {
+        try_multiply_column_types(self.lhs.data_type(), self.rhs.data_type())
+            .expect("Failed to multiply column types")
+    }
+
+    fn result_evaluate<'a>(
+        &self,
+        table_length: usize,
+        alloc: &'a Bump,
+        accessor: &'a dyn DataAccessor<C::Scalar>,
+    ) -> Column<'a, C::Scalar> {
+        let lhs_column: Column<'a, C::Scalar> =
+            self.lhs.result_evaluate(table_length, alloc, accessor);
+        let rhs_column: Column<'a, C::Scalar> =
+            self.rhs.result_evaluate(table_length, alloc, accessor);
+        let scalars = multiply_columns(&lhs_column, &rhs_column, alloc);
+        Column::Scalar(scalars)
+    }
+
+    #[tracing::instrument(
+        name = "proofs.sql.ast.and_expr.prover_evaluate",
+        level = "info",
+        skip_all
+    )]
+    fn prover_evaluate<'a>(
+        &self,
+        builder: &mut ProofBuilder<'a, C::Scalar>,
+        alloc: &'a Bump,
+        accessor: &'a dyn DataAccessor<C::Scalar>,
+    ) -> Column<'a, C::Scalar> {
+        let lhs_column: Column<'a, C::Scalar> = self.lhs.prover_evaluate(builder, alloc, accessor);
+        let rhs_column: Column<'a, C::Scalar> = self.rhs.prover_evaluate(builder, alloc, accessor);
+
+        // lhs_times_rhs
+        let lhs_times_rhs: &'a [C::Scalar] = multiply_columns(&lhs_column, &rhs_column, alloc);
+        builder.produce_intermediate_mle(lhs_times_rhs);
+
+        // subpolynomial: lhs_times_rhs - lhs * rhs
+        builder.produce_sumcheck_subpolynomial(
+            SumcheckSubpolynomialType::Identity,
+            vec![
+                (C::Scalar::one(), vec![Box::new(lhs_times_rhs)]),
+                (
+                    -C::Scalar::one(),
+                    vec![Box::new(lhs_column), Box::new(rhs_column)],
+                ),
+            ],
+        );
+        Column::Scalar(lhs_times_rhs)
+    }
+
+    fn verifier_evaluate(
+        &self,
+        builder: &mut VerificationBuilder<C>,
+        accessor: &dyn CommitmentAccessor<C>,
+    ) -> Result<C::Scalar, ProofError> {
+        let lhs = self.lhs.verifier_evaluate(builder, accessor)?;
+        let rhs = self.rhs.verifier_evaluate(builder, accessor)?;
+
+        // lhs_times_rhs
+        let lhs_times_rhs = builder.consume_intermediate_mle();
+
+        // subpolynomial: lhs_times_rhs - lhs * rhs
+        let eval = builder.mle_evaluations.random_evaluation * (lhs_times_rhs - lhs * rhs);
+        builder.produce_sumcheck_subpolynomial_evaluation(&eval);
+
+        // selection
+        Ok(lhs_times_rhs)
+    }
+
+    fn get_column_references(&self, columns: &mut HashSet<ColumnRef>) {
+        self.lhs.get_column_references(columns);
+        self.rhs.get_column_references(columns);
+    }
+}