From 4796ecf40a5fa18d4a2463a5bcc689bd62a718f5 Mon Sep 17 00:00:00 2001
From: ambrona <mac.ambrona@gmail.com>
Date: Wed, 24 Apr 2024 17:33:27 +0200
Subject: [PATCH] Remove redundant [selectors] field from [VerifieringKey]

Co-authored-by: alexandroszacharakis8 <107036523+alexandroszacharakis8@users.noreply.github.com>
---
 halo2_proofs/src/helpers.rs      | 12 --------
 halo2_proofs/src/plonk.rs        | 48 ++++++--------------------------
 halo2_proofs/src/plonk/keygen.rs |  1 -
 3 files changed, 9 insertions(+), 52 deletions(-)

diff --git a/halo2_proofs/src/helpers.rs b/halo2_proofs/src/helpers.rs
index faf7351a3e..6d9e8bf26e 100644
--- a/halo2_proofs/src/helpers.rs
+++ b/halo2_proofs/src/helpers.rs
@@ -101,18 +101,6 @@ pub trait SerdePrimeField: PrimeField + SerdeObject {
 }
 impl<F: PrimeField + SerdeObject> SerdePrimeField for F {}
 
-/// Convert a slice of `bool` into a `u8`.
-///
-/// Panics if the slice has length greater than 8.
-pub fn pack(bits: &[bool]) -> u8 {
-    let mut value = 0u8;
-    assert!(bits.len() <= 8);
-    for (bit_index, bit) in bits.iter().enumerate() {
-        value |= (*bit as u8) << bit_index;
-    }
-    value
-}
-
 /// Writes the first `bits.len()` bits of a `u8` into `bits`.
 pub fn unpack(byte: u8, bits: &mut [bool]) {
     for (bit_index, bit) in bits.iter_mut().enumerate() {
diff --git a/halo2_proofs/src/plonk.rs b/halo2_proofs/src/plonk.rs
index 78bfc21501..ba7ac58100 100644
--- a/halo2_proofs/src/plonk.rs
+++ b/halo2_proofs/src/plonk.rs
@@ -55,7 +55,6 @@ pub struct VerifyingKey<C: CurveAffine> {
     cs_degree: usize,
     /// The representative of this `VerifyingKey` in transcripts.
     transcript_repr: C::Scalar,
-    selectors: Vec<Vec<bool>>,
     /// Whether selector compression is turned on or not.
     compress_selectors: bool,
 }
@@ -89,17 +88,6 @@ where
             commitment.write(writer, format)?;
         }
         self.permutation.write(writer, format)?;
-
-        if !self.compress_selectors {
-            assert!(self.selectors.is_empty());
-        }
-        // write self.selectors
-        for selector in &self.selectors {
-            // since `selector` is filled with `bool`, we pack them 8 at a time into bytes and then write
-            for bits in selector.chunks(8) {
-                writer.write_all(&[crate::helpers::pack(bits)])?;
-            }
-        }
         Ok(())
     }
 
@@ -164,26 +152,17 @@ where
 
         let permutation = permutation::VerifyingKey::read(reader, &cs.permutation, format)?;
 
-        let (cs, selectors) = if compress_selectors {
-            // read selectors
-            let selectors: Vec<Vec<bool>> = vec![vec![false; 1 << k]; cs.num_selectors]
-                .into_iter()
-                .map(|mut selector| {
-                    let mut selector_bytes = vec![0u8; (selector.len() + 7) / 8];
-                    reader.read_exact(&mut selector_bytes)?;
-                    for (bits, byte) in selector.chunks_mut(8).zip(selector_bytes) {
-                        crate::helpers::unpack(byte, bits);
-                    }
-                    Ok(selector)
-                })
-                .collect::<io::Result<_>>()?;
+        let cs = if compress_selectors {
+            // We need to combine the selectors into fixed columns, we do this
+            // with dummy values, but this should not be a problem for the
+            // verifier, who does not care about the actual values (since the
+            // verifier will work with the fixed_commitments), but cares about
+            // the structure.
+            let selectors: Vec<Vec<bool>> = vec![vec![false; 1 << k]; cs.num_selectors];
             let (cs, _) = cs.compress_selectors(selectors.clone());
-            (cs, selectors)
+            cs
         } else {
-            // we still need to replace selectors with fixed Expressions in `cs`
-            let fake_selectors = vec![vec![]; cs.num_selectors];
-            let (cs, _) = cs.directly_convert_selectors_to_fixed(fake_selectors);
-            (cs, vec![])
+            cs
         };
 
         Ok(Self::from_parts(
@@ -191,7 +170,6 @@ where
             fixed_commitments,
             permutation,
             cs,
-            selectors,
             compress_selectors,
         ))
     }
@@ -225,12 +203,6 @@ impl<C: CurveAffine> VerifyingKey<C> {
     {
         10 + (self.fixed_commitments.len() * C::byte_length(format))
             + self.permutation.bytes_length(format)
-            + self.selectors.len()
-                * (self
-                    .selectors
-                    .get(0)
-                    .map(|selector| (selector.len() + 7) / 8)
-                    .unwrap_or(0))
     }
 
     fn from_parts(
@@ -238,7 +210,6 @@ impl<C: CurveAffine> VerifyingKey<C> {
         fixed_commitments: Vec<C>,
         permutation: permutation::VerifyingKey<C>,
         cs: ConstraintSystem<C::Scalar>,
-        selectors: Vec<Vec<bool>>,
         compress_selectors: bool,
     ) -> Self
     where
@@ -255,7 +226,6 @@ impl<C: CurveAffine> VerifyingKey<C> {
             cs_degree,
             // Temporary, this is not pinned.
             transcript_repr: C::Scalar::ZERO,
-            selectors,
             compress_selectors,
         };
 
diff --git a/halo2_proofs/src/plonk/keygen.rs b/halo2_proofs/src/plonk/keygen.rs
index d33a9325b9..80195eee65 100644
--- a/halo2_proofs/src/plonk/keygen.rs
+++ b/halo2_proofs/src/plonk/keygen.rs
@@ -278,7 +278,6 @@ where
         fixed_commitments,
         permutation_vk,
         cs,
-        assembly.selectors,
         compress_selectors,
     ))
 }