Refactor "booleanization" of objects.

src/circuit/boolean.rs

@@ -234,6 +234,47 @@ impl AllocatedBit {
     }
 }
 
+pub fn field_into_allocated_bits_be<E: Engine, CS: ConstraintSystem<E>, F: PrimeField>(
+    mut cs: CS,
+    value: Option<F>
+) -> Result<Vec<AllocatedBit>, SynthesisError>
+{
+    let values = match value {
+        Some(ref value) => {
+            let mut field_char = BitIterator::new(F::char());
+
+            let mut tmp = Vec::with_capacity(F::NUM_BITS as usize);
+
+            let mut found_one = false;
+            for b in BitIterator::new(value.into_repr()) {
+                // Skip leading bits
+                found_one |= field_char.next().unwrap();
+                if !found_one {
+                    continue;
+                }
+
+                tmp.push(Some(b));
+            }
+
+            assert_eq!(tmp.len(), F::NUM_BITS as usize);
+
+            tmp
+        },
+        None => {
+            vec![None; F::NUM_BITS as usize]
+        }
+    };
+
+    let bits = values.into_iter().enumerate().map(|(i, b)| {
+        AllocatedBit::alloc(
+            cs.namespace(|| format!("bit {}", i)),
+            b
+        )
+    }).collect::<Result<Vec<_>, SynthesisError>>()?;
+
+    Ok(bits)
+}
+
 /// This is a boolean value which may be either a constant or
 /// an interpretation of an `AllocatedBit`.
 #[derive(Clone)]
@@ -509,7 +550,11 @@ mod test {
     use pairing::bls12_381::{Bls12, Fr};
     use pairing::{Field, PrimeField, PrimeFieldRepr, BitIterator};
     use ::circuit::test::*;
-    use super::{AllocatedBit, Boolean};
+    use super::{
+        AllocatedBit,
+        Boolean,
+        field_into_allocated_bits_be
+    };
 
     #[test]
     fn test_allocated_bit() {
@@ -1129,4 +1174,26 @@ mod test {
             }
         }
     }
+
+    #[test]
+    fn test_field_into_allocated_bits_be() {
+        let mut cs = TestConstraintSystem::<Bls12>::new();
+
+        let r = Fr::from_str("9147677615426976802526883532204139322118074541891858454835346926874644257775").unwrap();
+
+        let bits = field_into_allocated_bits_be(&mut cs, Some(r)).unwrap();
+
+        assert!(cs.is_satisfied());
+
+        assert_eq!(bits.len(), 255);
+
+        assert_eq!(bits[0].value.unwrap(), false);
+        assert_eq!(bits[1].value.unwrap(), false);
+        assert_eq!(bits[2].value.unwrap(), true);
+        assert_eq!(bits[3].value.unwrap(), false);
+        assert_eq!(bits[4].value.unwrap(), true);
+        assert_eq!(bits[5].value.unwrap(), false);
+        assert_eq!(bits[20].value.unwrap(), true);
+        assert_eq!(bits[23].value.unwrap(), true);
+    }
 }

src/circuit/num.rs

@@ -17,6 +17,7 @@ use super::{
 };
 
 use super::boolean::{
+    self,
     Boolean,
     AllocatedBit
 };
@@ -76,39 +77,10 @@ impl<E: Engine> AllocatedNum<E> {
     ) -> Result<Vec<Boolean>, SynthesisError>
         where CS: ConstraintSystem<E>
     {
-        let bit_values = match self.value {
+        let bits = boolean::field_into_allocated_bits_be(
-            Some(value) => {
+            &mut cs,
-                let mut field_char = BitIterator::new(E::Fr::char());
+            self.value
-
+        )?;
-                let mut tmp = Vec::with_capacity(E::Fr::NUM_BITS as usize);
-
-                let mut found_one = false;
-                for b in BitIterator::new(value.into_repr()) {
-                    // Skip leading bits
-                    found_one |= field_char.next().unwrap();
-                    if !found_one {
-                        continue;
-                    }
-
-                    tmp.push(Some(b));
-                }
-
-                assert_eq!(tmp.len(), E::Fr::NUM_BITS as usize);
-
-                tmp
-            },
-            None => {
-                vec![None; E::Fr::NUM_BITS as usize]
-            }
-        };
-
-        let mut bits = vec![];
-        for (i, b) in bit_values.into_iter().enumerate() {
-            bits.push(AllocatedBit::alloc(
-                cs.namespace(|| format!("bit {}", i)),
-                b
-            )?);
-        }
 
         let mut lc = LinearCombination::zero();
         let mut coeff = E::Fr::one();