chore(backend): implement some circuit op logic (#165)

* Initial circuit op work

* Fix copy op

* Add more ops

* Fixes

* Code review

src/backends/plonky2/circuits/common.rs

@@ -1,8 +1,12 @@
 //! Common functionality to build Pod circuits with plonky2
 
+use crate::backends::plonky2::basetypes::D;
 use crate::backends::plonky2::mock::mainpod::Statement;
 use crate::backends::plonky2::mock::mainpod::{Operation, OperationArg};
-use crate::middleware::{Params, StatementArg, ToFields, Value, F, HASH_SIZE, VALUE_SIZE};
+use crate::middleware::{
+    NativeOperation, NativePredicate, Params, Predicate, StatementArg, ToFields, Value, F,
+    HASH_SIZE, VALUE_SIZE,
+};
 use crate::middleware::{OPERATION_ARG_F_LEN, STATEMENT_ARG_F_LEN};
 use anyhow::Result;
 use plonky2::field::extension::Extendable;
@@ -11,13 +15,42 @@ use plonky2::hash::hash_types::RichField;
 use plonky2::iop::target::{BoolTarget, Target};
 use plonky2::iop::witness::{PartialWitness, WitnessWrite};
 use plonky2::plonk::circuit_builder::CircuitBuilder;
-use std::iter;
+use std::{array, iter};
+
+pub const CODE_SIZE: usize = HASH_SIZE + 2;
 
 #[derive(Copy, Clone)]
 pub struct ValueTarget {
     pub elements: [Target; VALUE_SIZE],
 }
 
+impl ValueTarget {
+    pub fn zero(builder: &mut CircuitBuilder<F, D>) -> Self {
+        Self {
+            elements: [builder.zero(); VALUE_SIZE],
+        }
+    }
+
+    pub fn one(builder: &mut CircuitBuilder<F, D>) -> Self {
+        Self {
+            elements: array::from_fn(|i| {
+                if i == 0 {
+                    builder.one()
+                } else {
+                    builder.zero()
+                }
+            }),
+        }
+    }
+
+    pub fn from_slice(xs: &[Target]) -> Self {
+        assert_eq!(xs.len(), VALUE_SIZE);
+        Self {
+            elements: array::from_fn(|i| xs[i]),
+        }
+    }
+}
+
 #[derive(Clone)]
 pub struct StatementTarget {
     pub predicate: [Target; Params::predicate_size()],
@@ -25,12 +58,24 @@ pub struct StatementTarget {
 }
 
 impl StatementTarget {
-    pub fn to_flattened(&self) -> Vec<Target> {
-        self.predicate
-            .iter()
-            .chain(self.args.iter().flatten())
-            .cloned()
-            .collect()
+    pub fn new_native(
+        builder: &mut CircuitBuilder<F, D>,
+        params: &Params,
+        predicate: NativePredicate,
+        args: &[[Target; STATEMENT_ARG_F_LEN]],
+    ) -> Self {
+        let predicate_vec = builder.constants(&Predicate::Native(predicate).to_fields(params));
+        Self {
+            predicate: array::from_fn(|i| predicate_vec[i]),
+            args: args
+                .iter()
+                .map(|arg| *arg)
+                .chain(
+                    iter::repeat([builder.zero(); STATEMENT_ARG_F_LEN])
+                        .take(params.max_statement_args - args.len()),
+                )
+                .collect(),
+        }
     }
 
     pub fn set_targets(
@@ -51,6 +96,16 @@ impl StatementTarget {
         }
         Ok(())
     }
+
+    pub fn has_native_type(
+        &self,
+        builder: &mut CircuitBuilder<F, D>,
+        params: &Params,
+        t: NativePredicate,
+    ) -> BoolTarget {
+        let st_code = builder.constants(&Predicate::Native(t).to_fields(params));
+        builder.is_equal_slice(&self.predicate, &st_code)
+    }
 }
 
 // TODO: Implement Operation::to_field to determine the size of each element
@@ -79,6 +134,49 @@ impl OperationTarget {
         }
         Ok(())
     }
+
+    pub fn has_native_type(
+        &self,
+        builder: &mut CircuitBuilder<F, D>,
+        t: NativeOperation,
+    ) -> BoolTarget {
+        let one = builder.one();
+        let op_is_native = builder.is_equal(self.op_type[0], one);
+        let op_code = builder.constant(F::from_canonical_u64(t as u64));
+        let op_code_matches = builder.is_equal(self.op_type[1], op_code);
+        builder.and(op_is_native, op_code_matches)
+    }
+}
+
+/// Trait for target structs that may be converted to and from vectors
+/// of targets.
+pub trait Flattenable {
+    fn flatten(&self) -> Vec<Target>;
+    fn from_flattened(vs: &[Target]) -> Self;
+}
+
+impl Flattenable for StatementTarget {
+    fn flatten(&self) -> Vec<Target> {
+        self.predicate
+            .iter()
+            .chain(self.args.iter().flatten())
+            .cloned()
+            .collect()
+    }
+
+    fn from_flattened(v: &[Target]) -> Self {
+        let num_args = (v.len() - Params::predicate_size()) / STATEMENT_ARG_F_LEN;
+        assert_eq!(
+            v.len(),
+            Params::predicate_size() + num_args * STATEMENT_ARG_F_LEN
+        );
+        let predicate: [Target; Params::predicate_size()] = array::from_fn(|i| v[i]);
+        let args = (0..num_args)
+            .map(|i| array::from_fn(|j| v[Params::predicate_size() + i * STATEMENT_ARG_F_LEN + j]))
+            .collect();
+
+        Self { predicate, args }
+    }
 }
 
 pub trait CircuitBuilderPod<F: RichField + Extendable<D>, const D: usize> {
@@ -91,11 +189,27 @@ pub trait CircuitBuilderPod<F: RichField + Extendable<D>, const D: usize> {
     fn select_bool(&mut self, b: BoolTarget, x: BoolTarget, y: BoolTarget) -> BoolTarget;
     fn constant_value(&mut self, v: Value) -> ValueTarget;
     fn is_equal_slice(&mut self, xs: &[Target], ys: &[Target]) -> BoolTarget;
+
+    // Convenience methods for checking values.
+    /// Checks whether `xs` is right-padded with 0s so as to represent a `Value`.
+    fn statement_arg_is_value(&mut self, xs: &[Target]) -> BoolTarget;
+    /// Checks whether `x < y` if `b` is true. This involves checking
+    /// that `x` and `y` each consist of two `u32` limbs.
+    fn assert_less_if(&mut self, b: BoolTarget, x: ValueTarget, y: ValueTarget);
+
+    // Convenience methods for accessing and connecting elements of
+    // (vectors of) flattenables.
+    fn vec_ref<T: Flattenable>(&mut self, ts: &[T], i: Target) -> T;
+    fn select_flattenable<T: Flattenable>(&mut self, b: BoolTarget, x: &T, y: &T) -> T;
+    fn connect_flattenable<T: Flattenable>(&mut self, xs: &T, ys: &T);
+    fn is_equal_flattenable<T: Flattenable>(&mut self, xs: &T, ys: &T) -> BoolTarget;
+
+    // Convenience methods for Boolean into-iters.
+    fn all(&mut self, xs: impl IntoIterator<Item = BoolTarget>) -> BoolTarget;
+    fn any(&mut self, xs: impl IntoIterator<Item = BoolTarget>) -> BoolTarget;
 }
 
-impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilderPod<F, D>
-    for CircuitBuilder<F, D>
-{
+impl CircuitBuilderPod<F, D> for CircuitBuilder<F, D> {
     fn connect_slice(&mut self, xs: &[Target], ys: &[Target]) {
         assert_eq!(xs.len(), ys.len());
         for (x, y) in xs.iter().zip(ys.iter()) {
@@ -157,4 +271,110 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilderPod<F, D>
             self.and(ok, is_eq)
         })
     }
+
+    fn statement_arg_is_value(&mut self, xs: &[Target]) -> BoolTarget {
+        let zeros = iter::repeat(self.zero())
+            .take(STATEMENT_ARG_F_LEN - VALUE_SIZE)
+            .collect::<Vec<_>>();
+        self.is_equal_slice(&xs[VALUE_SIZE..], &zeros)
+    }
+
+    fn assert_less_if(&mut self, b: BoolTarget, x: ValueTarget, y: ValueTarget) {
+        const NUM_BITS: usize = 32;
+
+        // Lt assertion with 32-bit range check.
+        let assert_limb_lt = |builder: &mut Self, x, y| {
+            // Check that targets fit within `NUM_BITS` bits.
+            builder.range_check(x, NUM_BITS);
+            builder.range_check(y, NUM_BITS);
+            // Check that `y-1-x` fits within `NUM_BITS` bits.
+            let one = builder.one();
+            let y_minus_one = builder.sub(y, one);
+            let expr = builder.sub(y_minus_one, x);
+            builder.range_check(expr, NUM_BITS);
+        };
+
+        // If b is false, replace `x` and `y` with dummy values.
+        let zero = ValueTarget::zero(self);
+        let one = ValueTarget::one(self);
+        let x = self.select_value(b, x, zero);
+        let y = self.select_value(b, y, one);
+
+        // `x` and `y` should only have two limbs each.
+        x.elements
+            .into_iter()
+            .skip(2)
+            .for_each(|l| self.assert_zero(l));
+        y.elements
+            .into_iter()
+            .skip(2)
+            .for_each(|l| self.assert_zero(l));
+
+        let big_limbs_eq = self.is_equal(x.elements[1], y.elements[1]);
+        let lhs = self.select(big_limbs_eq, x.elements[0], x.elements[1]);
+        let rhs = self.select(big_limbs_eq, y.elements[0], y.elements[1]);
+        assert_limb_lt(self, lhs, rhs);
+    }
+
+    fn vec_ref<T: Flattenable>(&mut self, ts: &[T], i: Target) -> T {
+        // TODO: Revisit this when we need more than 64 statements.
+        let vector_ref = |builder: &mut CircuitBuilder<F, D>, v: &[Target], i| {
+            assert!(v.len() <= 64);
+            builder.random_access(i, v.to_vec())
+        };
+        let matrix_row_ref = |builder: &mut CircuitBuilder<F, D>, m: &[Vec<Target>], i| {
+            let num_rows = m.len();
+            let num_columns = m
+                .get(0)
+                .map(|row| {
+                    let row_len = row.len();
+                    assert!(m.iter().all(|row| row.len() == row_len));
+                    row_len
+                })
+                .unwrap_or(0);
+            (0..num_columns)
+                .map(|j| {
+                    vector_ref(
+                        builder,
+                        &(0..num_rows).map(|i| m[i][j]).collect::<Vec<_>>(),
+                        i,
+                    )
+                })
+                .collect::<Vec<_>>()
+        };
+
+        let flattened_ts = ts.iter().map(|t| t.flatten()).collect::<Vec<_>>();
+        T::from_flattened(&matrix_row_ref(self, &flattened_ts, i))
+    }
+
+    fn select_flattenable<T: Flattenable>(&mut self, b: BoolTarget, x: &T, y: &T) -> T {
+        let flattened_x = x.flatten();
+        let flattened_y = y.flatten();
+
+        T::from_flattened(
+            &iter::zip(flattened_x, flattened_y)
+                .map(|(x, y)| self.select(b, x, y))
+                .collect::<Vec<_>>(),
+        )
+    }
+
+    fn connect_flattenable<T: Flattenable>(&mut self, xs: &T, ys: &T) {
+        self.connect_slice(&xs.flatten(), &ys.flatten())
+    }
+
+    fn is_equal_flattenable<T: Flattenable>(&mut self, xs: &T, ys: &T) -> BoolTarget {
+        self.is_equal_slice(&xs.flatten(), &ys.flatten())
+    }
+
+    fn all(&mut self, xs: impl IntoIterator<Item = BoolTarget>) -> BoolTarget {
+        xs.into_iter()
+            .reduce(|a, b| self.and(a, b))
+            .unwrap_or(self._true())
+    }
+
+    fn any(&mut self, xs: impl IntoIterator<Item = BoolTarget>) -> BoolTarget {
+        xs.into_iter()
+            .reduce(|a, b| self.or(a, b))
+            .unwrap_or(self._false())
+    }
 }