From a8cbbee3925d832b9ee7c278d0f07789008110e2 Mon Sep 17 00:00:00 2001
From: collin <collin.chin@berkeley.edu>
Date: Thu, 25 Jun 2020 17:19:32 -0700
Subject: [PATCH] fix integer and field gadgets

---
 compiler/src/constraints/comparator.rs |  2 +-
 compiler/src/constraints/integer.rs    | 12 ++++++++++--
 compiler/src/field/mod.rs              |  4 ++--
 3 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/compiler/src/constraints/comparator.rs b/compiler/src/constraints/comparator.rs
index a22c6ede4d..34b75ead66 100644
--- a/compiler/src/constraints/comparator.rs
+++ b/compiler/src/constraints/comparator.rs
@@ -14,7 +14,7 @@ where
     Self: EvaluateLtGadget<F>,
 {
     fn greater_than<CS: ConstraintSystem<F>>(&self, cs: CS, other: &Self) -> Result<Boolean, SynthesisError> {
-        other.less_than(cs, other)
+        other.less_than(cs, self)
     }
 
     fn less_than_or_equal<CS: ConstraintSystem<F>>(&self, cs: CS, other: &Self) -> Result<Boolean, SynthesisError> {
diff --git a/compiler/src/constraints/integer.rs b/compiler/src/constraints/integer.rs
index aa8b66991a..4c7331e2bf 100644
--- a/compiler/src/constraints/integer.rs
+++ b/compiler/src/constraints/integer.rs
@@ -458,9 +458,17 @@ impl<F: Field + PrimeField> EvaluateLtGadget<F> for Integer {
             .zip(other.to_bits_le().iter().rev())
             .enumerate()
         {
-            let is_less = Boolean::and(&mut cs, self_bit, &other_bit.not())?;
+            // is_greater = a & !b
+            // only true when a > b
+            let is_greater = Boolean::and(cs.ns(|| format!("a and not b [{}]", i)), self_bit, &other_bit.not())?;
 
-            if is_less.eq(&Boolean::constant(true)) {
+            // is_less = !a & b
+            // only true when a < b
+            let is_less = Boolean::and(cs.ns(|| format!("not a and b [{}]", i)), &self_bit.not(), other_bit)?;
+
+            if is_greater.get_value().unwrap() {
+                return Ok(is_greater.not());
+            } else if is_less.get_value().unwrap() {
                 return Ok(is_less);
             } else if i == self.to_bits_le().len() - 1 {
                 return Ok(is_less);
diff --git a/compiler/src/field/mod.rs b/compiler/src/field/mod.rs
index 6db0f95a24..69a894e52f 100644
--- a/compiler/src/field/mod.rs
+++ b/compiler/src/field/mod.rs
@@ -224,9 +224,9 @@ impl<F: Field + PrimeField> EvaluateLtGadget<F> for FieldType<F> {
                 })
             }
             (FieldType::Allocated(first), FieldType::Allocated(second)) => {
-                let bool_option = first.value.and_then(|a| second.value.map(|b| a.eq(&b)));
+                let bool_option = first.value.and_then(|a| second.value.map(|b| a.lt(&b)));
 
-                Boolean::alloc(&mut cs.ns(|| "evaluate_equal"), || {
+                Boolean::alloc(&mut cs.ns(|| "less than"), || {
                     bool_option.ok_or(SynthesisError::AssignmentMissing)
                 })
             }