hashes: Add const hash engine constructors

Add `const` constructors to all hash engines. Call through to
`Self::new` in `default` impls on `HashEngine`.

hashes/src/ripemd160.rs

@@ -51,9 +51,10 @@ pub struct HashEngine {
     length: usize,
 }
 
-impl Default for HashEngine {
-    fn default() -> Self {
-        HashEngine {
+impl HashEngine {
+    /// Creates a new SHA256 hash engine.
+    pub const fn new() -> Self {
+        Self {
             h: [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476, 0xc3d2e1f0],
             length: 0,
             buffer: [0; BLOCK_SIZE],
@@ -61,6 +62,10 @@ impl Default for HashEngine {
     }
 }
 
+impl Default for HashEngine {
+    fn default() -> Self { Self::new() }
+}
+
 impl crate::HashEngine for HashEngine {
     type MidState = [u8; 20];
 

hashes/src/sha1.rs

@@ -43,9 +43,10 @@ pub struct HashEngine {
     length: usize,
 }
 
-impl Default for HashEngine {
-    fn default() -> Self {
-        HashEngine {
+impl HashEngine {
+    /// Creates a new SHA1 hash engine.
+    pub const fn new() -> Self {
+        Self {
             h: [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476, 0xc3d2e1f0],
             length: 0,
             buffer: [0; BLOCK_SIZE],
@@ -53,6 +54,10 @@ impl Default for HashEngine {
     }
 }
 
+impl Default for HashEngine {
+    fn default() -> Self { Self::new() }
+}
+
 impl crate::HashEngine for HashEngine {
     type MidState = [u8; 20];
 

hashes/src/sha256.rs

@@ -59,9 +59,10 @@ pub struct HashEngine {
     length: usize,
 }
 
-impl Default for HashEngine {
-    fn default() -> Self {
-        HashEngine {
+impl HashEngine {
+    /// Creates a new SHA256 hash engine.
+    pub const fn new() -> Self {
+        Self {
             h: [
                 0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab,
                 0x5be0cd19,
@@ -72,6 +73,10 @@ impl Default for HashEngine {
     }
 }
 
+impl Default for HashEngine {
+    fn default() -> Self { Self::new() }
+}
+
 impl crate::HashEngine for HashEngine {
     type MidState = Midstate;
 

hashes/src/sha384.rs

@@ -23,11 +23,13 @@ fn from_engine(e: HashEngine) -> Hash {
 #[derive(Clone)]
 pub struct HashEngine(sha512::HashEngine);
 
+impl HashEngine {
+    /// Creates a new SHA384 hash engine.
+    pub const fn new() -> Self { Self(sha512::HashEngine::sha384()) }
+}
+
 impl Default for HashEngine {
-    #[rustfmt::skip]
-    fn default() -> Self {
-        HashEngine(sha512::HashEngine::sha384())
-    }
+    fn default() -> Self { Self::new() }
 }
 
 impl crate::HashEngine for HashEngine {

hashes/src/sha512.rs

@@ -52,10 +52,11 @@ pub struct HashEngine {
     buffer: [u8; BLOCK_SIZE],
 }
 
-impl Default for HashEngine {
+impl HashEngine {
+    /// Creates a new SHA512 hash engine.
     #[rustfmt::skip]
-    fn default() -> Self {
-        HashEngine {
+    pub const fn new() -> Self {
+        Self {
             h: [
                 0x6a09e667f3bcc908, 0xbb67ae8584caa73b, 0x3c6ef372fe94f82b, 0xa54ff53a5f1d36f1,
                 0x510e527fade682d1, 0x9b05688c2b3e6c1f, 0x1f83d9abfb41bd6b, 0x5be0cd19137e2179,
@@ -66,10 +67,14 @@ impl Default for HashEngine {
     }
 }
 
+impl Default for HashEngine {
+    fn default() -> Self { Self::new() }
+}
+
 impl HashEngine {
-    /// Constructs a hash engine suitable for use inside the default `sha512_256::HashEngine`.
+    /// Constructs a hash engine suitable for use constructing a `sha512_256::HashEngine`.
     #[rustfmt::skip]
-    pub(crate) fn sha512_256() -> Self {
+    pub(crate) const fn sha512_256() -> Self {
         HashEngine {
             h: [
                 0x22312194fc2bf72c, 0x9f555fa3c84c64c2, 0x2393b86b6f53b151, 0x963877195940eabd,
@@ -80,9 +85,9 @@ impl HashEngine {
         }
     }
 
-    /// Constructs a hash engine suitable for use inside the default `sha384::HashEngine`.
+    /// Constructs a hash engine suitable for constructing `sha384::HashEngine`.
     #[rustfmt::skip]
-    pub(crate) fn sha384() -> Self {
+    pub(crate) const fn sha384() -> Self {
         HashEngine {
             h: [
                 0xcbbb9d5dc1059ed8, 0x629a292a367cd507, 0x9159015a3070dd17, 0x152fecd8f70e5939,

hashes/src/sha512_256.rs

@@ -33,11 +33,13 @@ fn from_engine(e: HashEngine) -> Hash {
 #[derive(Clone)]
 pub struct HashEngine(sha512::HashEngine);
 
+impl HashEngine {
+    /// Creates a new SHA512/256 hash engine.
+    pub const fn new() -> Self { Self(sha512::HashEngine::sha512_256()) }
+}
+
 impl Default for HashEngine {
-    #[rustfmt::skip]
-    fn default() -> Self {
-        HashEngine(sha512::HashEngine::sha512_256())
-    }
+    fn default() -> Self { Self::new() }
 }
 
 impl crate::HashEngine for HashEngine {