fix black box func call inputs comments

Author: vezenovm

acvm-repo/acir/src/circuit/opcodes.rs

@@ -68,16 +68,14 @@ pub enum Opcode<F: AcirField> {
     /// Often used for exposing more efficient implementations of
     /// SNARK-unfriendly computations.
     ///
-    /// All black box functions take as input a tuple `(witness, num_bits)`,
-    /// where `num_bits` is a constant representing the bit size of the input
-    /// witness, and they have one or several witnesses as output.
+    /// All black box functions input is specified as [FunctionInput],
+    /// and they have one or several witnesses as output.
     ///
     /// Some more advanced computations assume that the proving system has an
     /// 'embedded curve'. It is a curve that cycles with the main curve of the
     /// proving system, i.e the scalar field of the embedded curve is the base
     /// field of the main one, and vice-versa.
-    ///
-    /// Aztec's Barretenberg uses BN254 as the main curve and Grumpkin as the
+    /// e.g. Aztec's Barretenberg uses BN254 as the main curve and Grumpkin as the
     /// embedded curve.
     BlackBoxFuncCall(BlackBoxFuncCall<F>),
 

acvm-repo/acir/src/circuit/opcodes/black_box_function_call.rs

@@ -6,20 +6,25 @@ use crate::{AcirField, BlackBoxFunc};
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
 use thiserror::Error;
 
-// Note: Some functions will not use all of the witness
-// So we need to supply how many bits of the witness is needed
-
+/// Enumeration for black box function inputs
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize, Hash)]
 #[cfg_attr(feature = "arb", derive(proptest_derive::Arbitrary))]
 pub enum ConstantOrWitnessEnum<F> {
+    /// A constant field element
     Constant(F),
+    /// A witness element, representing dynamic inputs
     Witness(Witness),
 }
 
+/// Input to a black box call
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize, Hash)]
 #[cfg_attr(feature = "arb", derive(proptest_derive::Arbitrary))]
 pub struct FunctionInput<F> {
+    /// The actual input value
     input: ConstantOrWitnessEnum<F>,
+    /// A constant representing the bit size of the input value
+    /// Some functions will not use all of the witness
+    /// So we need to supply how many bits of the witness is needed
     num_bits: u32,
 }
 
@@ -81,6 +86,11 @@ impl<F: std::fmt::Display> std::fmt::Display for FunctionInput<F> {
     }
 }
 
+/// These opcodes represent a specialized computation.
+/// Even if any computation can be done using only assert-zero opcodes,
+/// it is not always efficient.
+/// Some proving systems, can implement several computations more efficiently using
+/// techniques such as custom gates and lookup tables.
 #[derive(Clone, PartialEq, Eq, Serialize, Deserialize, Hash)]
 pub enum BlackBoxFuncCall<F> {
     /// Ciphers (encrypts) the provided plaintext using AES128 in CBC mode,