From d594b8fc2d20c3969be64873a5f802191032c74f Mon Sep 17 00:00:00 2001
From: wborgeaud <williamborgeaud@gmail.com>
Date: Fri, 17 Dec 2021 08:46:07 +0100
Subject: [PATCH 1/2] Convert chunks of 7 bytes instead of 8

---
 src/hash/hash_types.rs | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/src/hash/hash_types.rs b/src/hash/hash_types.rs
index 19228b41..e645b5c3 100644
--- a/src/hash/hash_types.rs
+++ b/src/hash/hash_types.rs
@@ -3,8 +3,6 @@ use serde::{Deserialize, Deserializer, Serialize, Serializer};
 
 use crate::field::field_types::{Field, PrimeField, RichField};
 use crate::iop::target::Target;
-use crate::util::ceil_div_usize;
-use crate::util::serialization::Buffer;
 
 /// Represents a ~256 bit hash output.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, Serialize, Deserialize)]
@@ -162,10 +160,13 @@ impl<const N: usize> From<BytesHash<N>> for u64 {
 
 impl<F: RichField, const N: usize> From<BytesHash<N>> for Vec<F> {
     fn from(hash: BytesHash<N>) -> Self {
-        let n = hash.0.len();
-        let mut v = hash.0.to_vec();
-        v.resize(ceil_div_usize(n, 8) * 8, 0);
-        let mut buffer = Buffer::new(v);
-        buffer.read_field_vec(buffer.len() / 8).unwrap()
+        hash.0
+            .chunks(7)
+            .map(|bytes| {
+                let mut arr = [0; 8];
+                arr[..bytes.len()].copy_from_slice(bytes);
+                F::from_canonical_u64(u64::from_le_bytes(arr))
+            })
+            .collect()
     }
 }

From 0538511c9dcb00681f64028ab959d1ebee17da47 Mon Sep 17 00:00:00 2001
From: wborgeaud <williamborgeaud@gmail.com>
Date: Mon, 20 Dec 2021 09:22:23 +0100
Subject: [PATCH 2/2] Comment for why 7 bytes

---
 src/hash/hash_types.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/hash/hash_types.rs b/src/hash/hash_types.rs
index e645b5c3..79ca3950 100644
--- a/src/hash/hash_types.rs
+++ b/src/hash/hash_types.rs
@@ -161,6 +161,7 @@ impl<const N: usize> From<BytesHash<N>> for u64 {
 impl<F: RichField, const N: usize> From<BytesHash<N>> for Vec<F> {
     fn from(hash: BytesHash<N>) -> Self {
         hash.0
+            // Chunks of 7 bytes since 8 bytes would allow collisions.
             .chunks(7)
             .map(|bytes| {
                 let mut arr = [0; 8];