Merge rust-bitcoin#3982: hashes: Move from_engine functions

b98c489 hashes: Move from_engine functions (Tobin C. Harding)

Pull request description:

  In order to use the `general_hash_type` macro the must exist a standalone `from_engine` function. Currently this function is in different places in different modules. In an effort to make the `hashes` code easier to reason about put the functions right below the macro.

  Code move only, no other changes.

ACKs for top commit:
  Kixunil:
    ACK b98c489
  apoelstra:
    ACK b98c489; successfully ran local tests

Tree-SHA512: 8dfbf2b422d078d687708fa94a478ca597fae141f5c1f0a318a36152ca33f4760bb0545ab67523c558a8c3b8d258356975c5e357600d0ac980d473250a2af20e

hashes/src/hash160.rs

@@ -15,6 +15,15 @@ crate::internal_macros::general_hash_type! {
     "Output of the Bitcoin HASH160 hash function. (RIPEMD160(SHA256))"
 }
 
+fn from_engine(e: HashEngine) -> Hash {
+    let sha2 = sha256::Hash::from_engine(e.0);
+    let rmd = ripemd160::Hash::hash(sha2.as_byte_array());
+
+    let mut ret = [0; 20];
+    ret.copy_from_slice(rmd.as_byte_array());
+    Hash(ret)
+}
+
 /// Engine to compute HASH160 hash function.
 #[derive(Clone)]
 pub struct HashEngine(sha256::HashEngine);
@@ -34,15 +43,6 @@ impl crate::HashEngine for HashEngine {
     fn n_bytes_hashed(&self) -> u64 { self.0.n_bytes_hashed() }
 }
 
-fn from_engine(e: HashEngine) -> Hash {
-    let sha2 = sha256::Hash::from_engine(e.0);
-    let rmd = ripemd160::Hash::hash(sha2.as_byte_array());
-
-    let mut ret = [0; 20];
-    ret.copy_from_slice(rmd.as_byte_array());
-    Hash(ret)
-}
-
 #[cfg(test)]
 mod tests {
     #[test]

hashes/src/sha256d.rs

@@ -10,6 +10,15 @@ crate::internal_macros::general_hash_type! {
     "Output of the SHA256d hash function."
 }
 
+fn from_engine(e: HashEngine) -> Hash {
+    let sha2 = sha256::Hash::from_engine(e.0);
+    let sha2d = sha256::Hash::hash(sha2.as_byte_array());
+
+    let mut ret = [0; 32];
+    ret.copy_from_slice(sha2d.as_byte_array());
+    Hash(ret)
+}
+
 /// Engine to compute SHA256d hash function.
 #[derive(Clone)]
 pub struct HashEngine(sha256::HashEngine);
@@ -29,15 +38,6 @@ impl crate::HashEngine for HashEngine {
     fn n_bytes_hashed(&self) -> u64 { self.0.n_bytes_hashed() }
 }
 
-fn from_engine(e: HashEngine) -> Hash {
-    let sha2 = sha256::Hash::from_engine(e.0);
-    let sha2d = sha256::Hash::hash(sha2.as_byte_array());
-
-    let mut ret = [0; 32];
-    ret.copy_from_slice(sha2d.as_byte_array());
-    Hash(ret)
-}
-
 #[cfg(test)]
 mod tests {
     #[allow(unused_imports)] // whether this is used depends on features