From 96784b9cfa6746204994c32cf9d9a1f239f3d24f Mon Sep 17 00:00:00 2001
From: "Tobin C. Harding" <me@tobin.cc>
Date: Tue, 20 Jun 2023 04:21:28 +1000
Subject: [PATCH] Make sha512::HashEngine fields private

Recently we made the hash engine fields pub crate so that `sha512_256`
could construct a hash engine with different constants. We can make the
code slightly cleaner by adding a pub crate constructor and making the
fields private again.

Idea from Kixunil:

  https://github.com/rust-bitcoin/rust-bitcoin/pull/1413#pullrequestreview-1197207593
---
 hashes/src/sha512.rs     | 21 ++++++++++++++++++---
 hashes/src/sha512_256.rs | 12 ++----------
 2 files changed, 20 insertions(+), 13 deletions(-)

diff --git a/hashes/src/sha512.rs b/hashes/src/sha512.rs
index 58877c92..034b3a1a 100644
--- a/hashes/src/sha512.rs
+++ b/hashes/src/sha512.rs
@@ -17,9 +17,9 @@ pub(crate) const BLOCK_SIZE: usize = 128;
 /// Engine to compute SHA512 hash function.
 #[derive(Clone)]
 pub struct HashEngine {
-    pub(crate) h: [u64; 8],
-    pub(crate) length: usize,
-    pub(crate) buffer: [u8; BLOCK_SIZE],
+    h: [u64; 8],
+    length: usize,
+    buffer: [u8; BLOCK_SIZE],
 }
 
 impl Default for HashEngine {
@@ -36,6 +36,21 @@ impl Default for HashEngine {
     }
 }
 
+impl HashEngine {
+    /// Constructs a hash engine suitable for use inside the default `sha512_256::HashEngine`.
+    #[rustfmt::skip]
+    pub(crate) fn sha512_256() -> Self {
+        HashEngine {
+            h: [
+                0x22312194fc2bf72c, 0x9f555fa3c84c64c2, 0x2393b86b6f53b151, 0x963877195940eabd,
+                0x96283ee2a88effe3, 0xbe5e1e2553863992, 0x2b0199fc2c85b8aa, 0x0eb72ddc81c52ca2,
+            ],
+            length: 0,
+            buffer: [0; BLOCK_SIZE],
+        }
+    }
+}
+
 impl crate::HashEngine for HashEngine {
     type MidState = [u8; 64];
 
diff --git a/hashes/src/sha512_256.rs b/hashes/src/sha512_256.rs
index 6bef7bec..27d90d68 100644
--- a/hashes/src/sha512_256.rs
+++ b/hashes/src/sha512_256.rs
@@ -11,7 +11,6 @@ use core::ops::Index;
 use core::slice::SliceIndex;
 use core::str;
 
-use crate::sha512::BLOCK_SIZE;
 use crate::{sha512, FromSliceError};
 
 /// Engine to compute SHA512/256 hash function.
@@ -26,14 +25,7 @@ pub struct HashEngine(sha512::HashEngine);
 impl Default for HashEngine {
     #[rustfmt::skip]
     fn default() -> Self {
-        HashEngine(sha512::HashEngine {
-            h: [
-                0x22312194fc2bf72c, 0x9f555fa3c84c64c2, 0x2393b86b6f53b151, 0x963877195940eabd,
-                0x96283ee2a88effe3, 0xbe5e1e2553863992, 0x2b0199fc2c85b8aa, 0x0eb72ddc81c52ca2,
-            ],
-            length: 0,
-            buffer: [0; BLOCK_SIZE],
-        })
+        HashEngine(sha512::HashEngine::sha512_256())
     }
 }
 
@@ -44,7 +36,7 @@ impl crate::HashEngine for HashEngine {
 
     const BLOCK_SIZE: usize = sha512::BLOCK_SIZE;
 
-    fn n_bytes_hashed(&self) -> usize { self.0.length }
+    fn n_bytes_hashed(&self) -> usize { self.0.n_bytes_hashed() }
 
     fn input(&mut self, inp: &[u8]) { self.0.input(inp); }
 }