switch gate (in progress)

src/gates/mod.rs

@@ -14,6 +14,7 @@ pub(crate) mod noop;
 pub(crate) mod public_input;
 pub mod random_access;
 pub mod reducing;
+pub mod switch;
 
 #[cfg(test)]
 mod gate_testing;

src/gates/random_access.rs

@@ -27,7 +27,7 @@ impl<F: Extendable<D>, const D: usize> RandomAccessGate<F, D> {
         }
     }
 
-    pub fn wires_access_index(&self) -> usize {
+    pub fn wire_access_index(&self) -> usize {
         0
     }
 
@@ -67,7 +67,7 @@ impl<F: Extendable<D>, const D: usize> Gate<F, D> for RandomAccessGate<F, D> {
     }
 
     fn eval_unfiltered(&self, vars: EvaluationVars<F, D>) -> Vec<F::Extension> {
-        let access_index = vars.local_wires[self.wires_access_index()];
+        let access_index = vars.local_wires[self.wire_access_index()];
         let list_items = (0..self.vec_size)
             .map(|i| vars.get_local_ext_algebra(self.wires_list_item(i)))
             .collect::<Vec<_>>();
@@ -93,7 +93,7 @@ impl<F: Extendable<D>, const D: usize> Gate<F, D> for RandomAccessGate<F, D> {
     }
 
     fn eval_unfiltered_base(&self, vars: EvaluationVarsBase<F>) -> Vec<F> {
-        let access_index = vars.local_wires[self.wires_access_index()];
+        let access_index = vars.local_wires[self.wire_access_index()];
         let list_items = (0..self.vec_size)
             .map(|i| vars.get_local_ext(self.wires_list_item(i)))
             .collect::<Vec<_>>();
@@ -124,7 +124,7 @@ impl<F: Extendable<D>, const D: usize> Gate<F, D> for RandomAccessGate<F, D> {
         builder: &mut CircuitBuilder<F, D>,
         vars: EvaluationTargets<D>,
     ) -> Vec<ExtensionTarget<D>> {
-        let access_index = vars.local_wires[self.wires_access_index()];
+        let access_index = vars.local_wires[self.wire_access_index()];
         let list_items = (0..self.vec_size)
             .map(|i| vars.get_local_ext_algebra(self.wires_list_item(i)))
             .collect::<Vec<_>>();
@@ -200,7 +200,7 @@ impl<F: Extendable<D>, const D: usize> SimpleGenerator<F> for RandomAccessGenera
         let local_targets = |inputs: Range<usize>| inputs.map(local_target);
 
         let mut deps = Vec::new();
-        deps.push(local_target(self.gate.wires_access_index()));
+        deps.push(local_target(self.gate.wire_access_index()));
         deps.extend(local_targets(self.gate.wires_claimed_element()));
         for i in 0..self.gate.vec_size {
             deps.extend(local_targets(self.gate.wires_list_item(i)));
@@ -218,7 +218,7 @@ impl<F: Extendable<D>, const D: usize> SimpleGenerator<F> for RandomAccessGenera
 
         // Compute the new vector and the values for equality_dummy and index_matches
         let vec_size = self.gate.vec_size;
-        let access_index_f = get_local_wire(self.gate.wires_access_index());
+        let access_index_f = get_local_wire(self.gate.wire_access_index());
 
         let access_index = access_index_f.to_canonical_u64() as usize;
         debug_assert!(
@@ -268,7 +268,7 @@ mod tests {
             _phantom: PhantomData,
         };
 
-        assert_eq!(gate.wires_access_index(), 0);
+        assert_eq!(gate.wire_access_index(), 0);
         assert_eq!(gate.wires_claimed_element(), 1..5);
         assert_eq!(gate.wires_list_item(0), 5..9);
         assert_eq!(gate.wires_list_item(2), 13..17);

src/gates/switch.rs

@@ -0,0 +1,356 @@
+use std::marker::PhantomData;
+use std::ops::Range;
+
+use crate::field::extension_field::target::ExtensionTarget;
+use crate::field::extension_field::{Extendable, FieldExtension};
+use crate::field::field_types::Field;
+use crate::gates::gate::Gate;
+use crate::iop::generator::{GeneratedValues, SimpleGenerator, WitnessGenerator};
+use crate::iop::target::Target;
+use crate::iop::wire::Wire;
+use crate::iop::witness::PartialWitness;
+use crate::plonk::circuit_builder::CircuitBuilder;
+use crate::plonk::circuit_data::CircuitConfig;
+use crate::plonk::vars::{EvaluationTargets, EvaluationVars, EvaluationVarsBase};
+
+/// A gate for checking that a particular value in a list matches a given
+#[derive(Clone, Debug)]
+pub(crate) struct SwitchGate<F: Extendable<D>, const D: usize, const CHUNK_SIZE: usize> {
+    num_copies: usize,
+    _phantom: PhantomData<F>,
+}
+
+impl<F: Extendable<D>, const D: usize, const CHUNK_SIZE: usize> SwitchGate<F, D, CHUNK_SIZE> {
+    pub fn new(config: CircuitConfig) -> Self {
+        let num_copies = Self::max_num_chunks(config.num_wires, config.num_routed_wires);
+        Self {
+            num_copies,
+            _phantom: PhantomData,
+        }
+    }
+
+    pub fn wire_switch_bool(&self, copy: usize) -> usize {
+        debug_assert!(copy < self.num_copies);
+        copy * (4 * CHUNK_SIZE + 1)
+    }
+
+    pub fn wire_first_input(&self, copy: usize, element: usize) {
+        debug_assert!(copy < self.num_copies);
+        debug_assert!(element < CHUNK_SIZE);
+        copy * (4 * CHUNK_SIZE + 1) + 1 + element
+    }
+
+    pub fn wire_second_input(&self, copy: usize, element: usize) {
+        debug_assert!(copy < self.num_copies);
+        debug_assert!(element < CHUNK_SIZE);
+        copy * (4 * CHUNK_SIZE + 1) + 1 + CHUNK_SIZE + element
+    }
+
+    pub fn wire_first_output(&self, copy: usize, element: usize) {
+        debug_assert!(copy < self.num_copies);
+        debug_assert!(element < CHUNK_SIZE);
+        copy * (4 * CHUNK_SIZE + 1) + 1 + 2 * CHUNK_SIZE + element
+    }
+
+    pub fn wire_second_output(&self, copy: usize, element: usize) {
+        debug_assert!(copy < self.num_copies);
+        debug_assert!(element < CHUNK_SIZE);
+        copy * (4 * CHUNK_SIZE + 1) + 1 + 3 * CHUNK_SIZE + element
+    }
+}
+
+impl<F: Extendable<D>, const D: usize, const CHUNK_SIZE: usize> Gate<F, D> for SwitchGate<F, D, CHUNK_SIZE> {
+    fn id(&self) -> String {
+        format!("{:?}<D={}>", self, D)
+    }
+
+    fn eval_unfiltered(&self, vars: EvaluationVars<F, D>) -> Vec<F::Extension> {
+        let mut constraints = Vec::with_capacity(self.num_constraints());
+        
+        for c in 0..self.num_copies {
+            let switch_bool = vars.local_wires[self.wire_switch_bool(c)];
+
+            for e in 0..CHUNK_SIZE {
+                let first_input = vars.local_wires[self.wire_first_input(c, e)];
+                let second_input = vars.local_wires[self.wire_second_input(c, e)];
+                let first_output = vars.local_wires[self.wire_first_output(c, e)];
+                let second_output = vars.local_wires[self.wire_second_output(c, e)];
+                
+                constraints.push(switch_bool * (first_input - second_output));
+                constraints.push(switch_bool * (second_input - first_output));
+                constraints.push((F::Extension::ONE - switch_bool) * (first_input - first_output));
+                constraints.push((F::Extension::ONE - switch_bool) * (second_input - second_output));
+            }
+        }
+
+        constraints
+    }
+
+    fn eval_unfiltered_base(&self, vars: EvaluationVarsBase<F, D>) -> Vec<F> {
+        let mut constraints = Vec::with_capacity(self.num_constraints());
+        
+        for c in 0..self.num_copies {
+            let switch_bool = vars.local_wires[self.wire_switch_bool(c)];
+
+            for e in 0..CHUNK_SIZE {
+                let first_input = vars.local_wires[self.wire_first_input(c, e)];
+                let second_input = vars.local_wires[self.wire_second_input(c, e)];
+                let first_output = vars.local_wires[self.wire_first_output(c, e)];
+                let second_output = vars.local_wires[self.wire_second_output(c, e)];
+                
+                constraints.push(switch_bool * (first_input - second_output));
+                constraints.push(switch_bool * (second_input - first_output));
+                constraints.push((F::ONE - switch_bool) * (first_input - first_output));
+                constraints.push((F::ONE - switch_bool) * (second_input - second_output));
+            }
+        }
+
+        constraints
+    }
+
+    fn eval_unfiltered_recursively(
+        &self,
+        builder: &mut CircuitBuilder<F, D>,
+        vars: EvaluationTargets<D>,
+    ) -> Vec<ExtensionTarget<D>> {
+        let mut constraints = Vec::with_capacity(self.num_constraints());
+        
+        let one = builder.one_extension();
+        for c in 0..self.num_copies {
+            let switch_bool = vars.local_wires[self.wire_switch_bool(c)];
+            let not_switch = builder.sub_extension(one, switch_bool);
+
+            for e in 0..CHUNK_SIZE {
+                let first_input = vars.local_wires[self.wire_first_input(c, e)];
+                let second_input = vars.local_wires[self.wire_second_input(c, e)];
+                let first_output = vars.local_wires[self.wire_first_output(c, e)];
+                let second_output = vars.local_wires[self.wire_second_output(c, e)];
+                
+                
+                let first_switched = builder.sub_extension(first_input, second_output);
+                let first_switched_constraint = builder.mul_extension(switch_bool, first_switched);
+                constraints.push(first_switched_constraint);
+
+                let second_switched = builder.sub_extension(second_input, first_output);
+                let second_switched_constraint = builder.mul_extension(switch_bool, second_switched);
+                constraints.push(second_switched_constraint);
+
+                let first_not_switched = builder.sub_extension(first_input, first_output);
+                let first_not_switched_constraint = builder.mul_extension(not_switch, first_not_switched);
+                constraints.push(first_not_switched_constraint);
+
+                let second_not_switched = builder.sub_extension(second_input, second_output);
+                let second_not_switched_constraint = builder.mul_extension(not_switch, second_not_switched);
+                constraints.push(second_not_switched_constraint);
+            }
+        }
+
+        constraints
+    }
+
+    fn generators(
+        &self,
+        gate_index: usize,
+        _local_constants: &[F],
+    ) -> Vec<Box<dyn WitnessGenerator<F>>> {
+        let gen = SwitchGenerator::<F, D> {
+            gate_index,
+            gate: self.clone(),
+        };
+        vec![Box::new(gen)]
+    }
+
+    fn num_wires(&self) -> usize {
+        self.wire_second_output(self.num_copies - 1, CHUNK_SIZE - 1) + 1
+    }
+
+    fn num_constants(&self) -> usize {
+        0
+    }
+
+    fn degree(&self) -> usize {
+        2
+    }
+
+    fn num_constraints(&self) -> usize {
+        4 * self.num_copies * CHUNK_SIZE
+    }
+}
+
+#[derive(Debug)]
+struct SwitchGenerator<F: Extendable<D>, const D: usize, const CHUNK_SIZE: usize> {
+    gate_index: usize,
+    gate: SwitchGate<F, D, CHUNK_SIZE>,
+}
+
+impl<F: Extendable<D>, const D: usize, const CHUNK_SIZE: usize> SimpleGenerator<F> for SwitchGenerator<F, D, CHUNK_SIZE> {
+    fn dependencies(&self) -> Vec<Target> {
+        let local_target = |input| Target::wire(self.gate_index, input);
+
+        let local_targets = |inputs: Range<usize>| inputs.map(local_target);
+
+        let mut deps = Vec::new();
+        for c in 0..self.gate.num_copies {
+            deps.push(local_target(self.gate.wire_switch_bool(c)));
+            for e in 0..CHUNK_SIZE {
+                deps.push(local_target(self.gate.wire_first_input(c, e)));
+                deps.push(local_target(self.gate.wire_second_input(c, e)));
+            }
+        }
+
+        deps
+    }
+
+    fn run_once(&self, witness: &PartialWitness<F>, out_buffer: &mut GeneratedValues<F>) {
+        let local_wire = |input| Wire {
+            gate: self.gate_index,
+            input,
+        };
+
+        let get_local_wire = |input| witness.get_wire(local_wire(input));
+
+        // Compute the new vector and the values for equality_dummy and index_matches
+        let vec_size = self.gate.vec_size;
+        let access_index_f = get_local_wire(self.gate.wires_access_index());
+
+        let access_index = access_index_f.to_canonical_u64() as usize;
+        debug_assert!(
+            access_index < vec_size,
+            "Access index {} is larger than the vector size {}",
+            access_index,
+            vec_size
+        );
+
+        for i in 0..vec_size {
+            let equality_dummy_wire = local_wire(self.gate.wire_equality_dummy_for_index(i));
+            let index_matches_wire = local_wire(self.gate.wire_index_matches_for_index(i));
+
+            if i == access_index {
+                out_buffer.set_wire(equality_dummy_wire, F::ONE);
+                out_buffer.set_wire(index_matches_wire, F::ONE);
+            } else {
+                out_buffer.set_wire(
+                    equality_dummy_wire,
+                    (F::from_canonical_usize(i) - F::from_canonical_usize(access_index)).inverse(),
+                );
+                out_buffer.set_wire(index_matches_wire, F::ZERO);
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::marker::PhantomData;
+
+    use anyhow::Result;
+
+    use crate::field::crandall_field::CrandallField;
+    use crate::field::extension_field::quartic::QuarticCrandallField;
+    use crate::field::field_types::Field;
+    use crate::gates::gate::Gate;
+    use crate::gates::gate_testing::{test_eval_fns, test_low_degree};
+    use crate::gates::switch::SwitchGate;
+    use crate::hash::hash_types::HashOut;
+    use crate::plonk::vars::EvaluationVars;
+
+    #[test]
+    fn wire_indices() {
+        let gate = SwitchGate::<CrandallField, 4, 3> {
+            num_copies: 3,
+            _phantom: PhantomData,
+        };
+
+
+        assert_eq!(gate.wire_switch_bool(0), 0);
+        assert_eq!(gate.wire_first_input(0, 0), 1);
+        assert_eq!(gate.wire_first_input(0, 2), 3);
+        assert_eq!(gate.wire_second_input(0, 0), 4);
+        assert_eq!(gate.wire_second_input(0, 2), 6);
+        assert_eq!(gate.wire_first_output(0, 0), 7);
+        assert_eq!(gate.wire_second_output(0, 2), 12);
+        assert_eq!(gate.wire_first_input(1, 0), 13);
+        assert_eq!(gate.wire_second_output(1, 2), 24);
+        assert_eq!(gate.wire_first_input(2, 0), 25);
+        assert_eq!(gate.wire_second_output(2, 2), 36);
+    }
+
+    #[test]
+    fn low_degree() {
+        test_low_degree::<CrandallField, _, 4>(SwitchGate::new(CircuitConfig::large_config()));
+    }
+
+    #[test]
+    fn eval_fns() -> Result<()> {
+        test_eval_fns::<CrandallField, _, 4>(SwitchGate::new(CircuitConfig::large_config()))
+    }
+
+    #[test]
+    fn test_gate_constraint() {
+        type F = CrandallField;
+        type FF = QuarticCrandallField;
+        const D: usize = 4;
+
+        /// Returns the local wires for a random access gate given the vector, element to compare,
+        /// and index.
+        fn get_wires(list: Vec<FF>, access_index: usize, claimed_element: FF) -> Vec<FF> {
+            let vec_size = list.len();
+
+            let mut v = Vec::new();
+            v.push(F::from_canonical_usize(access_index));
+            v.extend(claimed_element.0);
+            for j in 0..vec_size {
+                v.extend(list[j].0);
+            }
+
+            let mut equality_dummy_vals = Vec::new();
+            let mut index_matches_vals = Vec::new();
+            for i in 0..vec_size {
+                if i == access_index {
+                    equality_dummy_vals.push(F::ONE);
+                    index_matches_vals.push(F::ONE);
+                } else {
+                    equality_dummy_vals.push(
+                        (F::from_canonical_usize(i) - F::from_canonical_usize(access_index))
+                            .inverse(),
+                    );
+                    index_matches_vals.push(F::ZERO);
+                }
+            }
+
+            v.extend(equality_dummy_vals);
+            v.extend(index_matches_vals);
+
+            v.iter().map(|&x| x.into()).collect::<Vec<_>>()
+        }
+
+        let list = vec![FF::rand(); 3];
+        let access_index = 1;
+        let gate = SwitchGate::<F, D> {
+            vec_size: 3,
+            _phantom: PhantomData,
+        };
+
+        let good_claimed_element = list[access_index];
+        let good_vars = EvaluationVars {
+            local_constants: &[],
+            local_wires: &get_wires(list.clone(), access_index, good_claimed_element),
+            public_inputs_hash: &HashOut::rand(),
+        };
+        let bad_claimed_element = FF::rand();
+        let bad_vars = EvaluationVars {
+            local_constants: &[],
+            local_wires: &get_wires(list, access_index, bad_claimed_element),
+            public_inputs_hash: &HashOut::rand(),
+        };
+
+        assert!(
+            gate.eval_unfiltered(good_vars).iter().all(|x| x.is_zero()),
+            "Gate constraints are not satisfied."
+        );
+        assert!(
+            !gate.eval_unfiltered(bad_vars).iter().all(|x| x.is_zero()),
+            "Gate constraints are satisfied but shouold not be."
+        );
+    }
+}