From bdfe124b0cceda186fcd62f5d44bc6398e14442d Mon Sep 17 00:00:00 2001
From: Nicholas Ward <npward@berkeley.edu>
Date: Tue, 12 Oct 2021 14:20:39 -0700
Subject: [PATCH] multiple comparison

---
 src/gadgets/multiple_comparison.rs | 61 ++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)
 create mode 100644 src/gadgets/multiple_comparison.rs

diff --git a/src/gadgets/multiple_comparison.rs b/src/gadgets/multiple_comparison.rs
new file mode 100644
index 00000000..5291323d
--- /dev/null
+++ b/src/gadgets/multiple_comparison.rs
@@ -0,0 +1,61 @@
+use std::marker::PhantomData;
+
+use itertools::izip;
+
+use crate::field::extension_field::Extendable;
+use crate::field::field_types::{Field, RichField};
+use crate::gates::comparison::ComparisonGate;
+use crate::iop::generator::{GeneratedValues, SimpleGenerator};
+use crate::iop::target::{BoolTarget, Target};
+use crate::iop::witness::{PartitionWitness, Witness};
+use crate::plonk::circuit_builder::CircuitBuilder;
+use crate::util::ceil_div_usize;
+
+impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
+    /// Returns true if a is less than or equal to b, considered as limbs of a large value.
+    pub fn compare_lists(&mut self, a: Vec<Target>, b: Vec<Target>, num_bits: usize) -> BoolTarget {
+        assert_eq!(
+            a.len(),
+            b.len(),
+            "Permutation must have same number of inputs and outputs"
+        );
+        let n = a.len();
+
+        let chunk_size = 4;
+        let num_chunks = ceil_div_usize(num_bits, 4);
+
+        let one = self.one();
+        let mut result = self.one();
+        for i in 0..n {
+            let a_le_b_gate = ComparisonGate::new(num_bits, num_chunks);
+            let a_le_b_gate_index = self.add_gate(a_le_b_gate.clone(), vec![]);
+            self.connect(
+                Target::wire(a_le_b_gate_index, a_le_b_gate.wire_first_input()),
+                a[i],
+            );
+            self.connect(
+                Target::wire(a_le_b_gate_index, a_le_b_gate.wire_second_input()),
+                b[i],
+            );
+            let a_le_b_result = Target::wire(a_le_b_gate_index, a_le_b_gate.wire_result_bool());
+
+            let b_le_a_gate = ComparisonGate::new(num_bits, num_chunks);
+            let b_le_a_gate_index = self.add_gate(b_le_a_gate.clone(), vec![]);
+            self.connect(
+                Target::wire(b_le_a_gate_index, b_le_a_gate.wire_first_input()),
+                b[i],
+            );
+            self.connect(
+                Target::wire(b_le_a_gate_index, b_le_a_gate.wire_second_input()),
+                a[i],
+            );
+            let b_le_a_result = Target::wire(b_le_a_gate_index, b_le_a_gate.wire_result_bool());
+
+            let these_limbs_equal = self.mul(a_le_b_result, b_le_a_result);
+            let these_limbs_less_than = self.sub(one, b_le_a_result);
+            result = self.mul_add(these_limbs_equal, result, these_limbs_less_than);
+        }
+
+        BoolTarget::new_unsafe(result)
+    }
+}