From a924ac6b81ce8c2ccd5cd2df833bd9b2d47c26e5 Mon Sep 17 00:00:00 2001
From: Philipp Gackstatter <PhilippGackstatter@users.noreply.github.com>
Date: Wed, 25 Sep 2024 12:03:31 +0200
Subject: [PATCH] feat: Add size hint for digests (#330)

---
 CHANGELOG.md                  | 4 ++++
 src/hash/rescue/rpo/digest.rs | 8 ++++++++
 src/hash/rescue/rpx/digest.rs | 8 ++++++++
 3 files changed, 20 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1a29f47f..e3bc8d66 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.10.2 (TBD)
+
+* Implement `get_size_hint` for `RpoDigest` and `RpxDigest` and expose constants for their serialized size (#330).
+
 ## 0.10.1 (2024-09-13)
 
 * Added `Serializable` and `Deserializable` implementations for `PartialMmr` and `InOrderIndex` (#329).
diff --git a/src/hash/rescue/rpo/digest.rs b/src/hash/rescue/rpo/digest.rs
index 545b68dc..ff1bb66b 100644
--- a/src/hash/rescue/rpo/digest.rs
+++ b/src/hash/rescue/rpo/digest.rs
@@ -19,6 +19,9 @@ use crate::{
 pub struct RpoDigest([Felt; DIGEST_SIZE]);
 
 impl RpoDigest {
+    /// The serialized size of the digest in bytes.
+    pub const SERIALIZED_SIZE: usize = DIGEST_BYTES;
+
     pub const fn new(value: [Felt; DIGEST_SIZE]) -> Self {
         Self(value)
     }
@@ -423,6 +426,10 @@ impl Serializable for RpoDigest {
     fn write_into<W: ByteWriter>(&self, target: &mut W) {
         target.write_bytes(&self.as_bytes());
     }
+
+    fn get_size_hint(&self) -> usize {
+        Self::SERIALIZED_SIZE
+    }
 }
 
 impl Deserializable for RpoDigest {
@@ -476,6 +483,7 @@ mod tests {
         let mut bytes = vec![];
         d1.write_into(&mut bytes);
         assert_eq!(DIGEST_BYTES, bytes.len());
+        assert_eq!(bytes.len(), d1.get_size_hint());
 
         let mut reader = SliceReader::new(&bytes);
         let d2 = RpoDigest::read_from(&mut reader).unwrap();
diff --git a/src/hash/rescue/rpx/digest.rs b/src/hash/rescue/rpx/digest.rs
index d104d4f9..574c1531 100644
--- a/src/hash/rescue/rpx/digest.rs
+++ b/src/hash/rescue/rpx/digest.rs
@@ -19,6 +19,9 @@ use crate::{
 pub struct RpxDigest([Felt; DIGEST_SIZE]);
 
 impl RpxDigest {
+    /// The serialized size of the digest in bytes.
+    pub const SERIALIZED_SIZE: usize = DIGEST_BYTES;
+
     pub const fn new(value: [Felt; DIGEST_SIZE]) -> Self {
         Self(value)
     }
@@ -423,6 +426,10 @@ impl Serializable for RpxDigest {
     fn write_into<W: ByteWriter>(&self, target: &mut W) {
         target.write_bytes(&self.as_bytes());
     }
+
+    fn get_size_hint(&self) -> usize {
+        Self::SERIALIZED_SIZE
+    }
 }
 
 impl Deserializable for RpxDigest {
@@ -476,6 +483,7 @@ mod tests {
         let mut bytes = vec![];
         d1.write_into(&mut bytes);
         assert_eq!(DIGEST_BYTES, bytes.len());
+        assert_eq!(bytes.len(), d1.get_size_hint());
 
         let mut reader = SliceReader::new(&bytes);
         let d2 = RpxDigest::read_from(&mut reader).unwrap();