Improve prove finality structure

casper-finality-proofs/src/prove_finality/circuit.rs

@@ -17,10 +17,18 @@ impl Circuit for ProveFinality {
     fn define<L: PlonkParameters<D>, const D: usize>(builder: &mut CircuitBuilder<L, D>) {
         let source = builder.read::<CheckpointVariable>();
         let target = builder.read::<CheckpointVariable>();
-        let target_source_difference = builder.sub(target.epoch, source.epoch);
+        let slot = builder.read::<Gwei>();
+        let total_number_of_validators = builder.read::<Gwei>();
+        let justification_bits = builder.read::<JustificationBitsVariable>();
+        let previous_epoch_attested_validators = builder.read::<Gwei>();
+        let current_epoch_attested_validators = builder.read::<Gwei>();
 
+        let zero = builder.constant::<U64Variable>(0);
         let one = builder.constant::<U64Variable>(1);
         let two = builder.constant::<U64Variable>(2);
+        let thirty_two = builder.constant::<U64Variable>(32);
+
+        let target_source_difference = builder.sub(target.epoch, source.epoch);
         let target_source_difference_equals_one = builder.is_equal(target_source_difference, one);
         let target_source_difference_equals_two = builder.is_equal(target_source_difference, two);
         let target_source_difference_equals_one_or_two = builder.or(
@@ -29,22 +37,13 @@ impl Circuit for ProveFinality {
         );
         assert_is_true(builder, target_source_difference_equals_one_or_two);
 
-        let slot = builder.read::<Gwei>();
-        let zero = builder.constant::<U64Variable>(0);
-        let thirty_two = builder.constant::<U64Variable>(32);
-
         let current_epoch = builder.div(slot, thirty_two);
         let current_epoch_target_difference = builder.sub(current_epoch, target.epoch);
         let target_is_first_bit = builder.is_equal(current_epoch_target_difference, zero);
         let target_is_second_bit = builder.is_equal(current_epoch_target_difference, one);
         let is_target_first_or_second_bit = builder.or(target_is_first_bit, target_is_second_bit);
         assert_is_true(builder, is_target_first_or_second_bit);
 
-        let total_number_of_validators = builder.read::<Gwei>();
-        let justification_bits = builder.read::<JustificationBitsVariable>();
-        let previous_epoch_attested_validators = builder.read::<Gwei>();
-        let current_epoch_attested_validators = builder.read::<Gwei>();
-
         let new_justification_bits = process_justifications(
             builder,
             total_number_of_validators,
@@ -55,7 +54,7 @@ impl Circuit for ProveFinality {
 
         let new_justification_bits = new_justification_bits.bits.as_slice();
         let source_index = builder.sub(current_epoch, source.epoch);
-        let target_index = builder.sub(current_epoch, target.epoch);
+        let target_index = current_epoch_target_difference;
         for i in 0..4 {
             let current_index = builder.constant::<U64Variable>(i as u64);
             let in_range_source_index = builder.lte(current_index, source_index);