From: Mikko Rasa <tdb@tdb.fi>
Date: Wed, 17 Nov 2021 12:15:18 +0000 (+0200)
Subject: Add some more hash utility functions
X-Git-Url: http://git.tdb.fi/?a=commitdiff_plain;h=7533857dc04c1f3a1fd6c509a194b4d7f0ab3cdd;p=libs%2Fcore.git

Add some more hash utility functions
---

diff --git a/source/core/hash.h b/source/core/hash.h
index a7e8cb1..e2201cf 100644
--- a/source/core/hash.h
+++ b/source/core/hash.h
@@ -62,6 +62,38 @@ struct HashTraits<N, 3>
 	static constexpr bool folded = true;
 };
 
+/**
+Computes a single round of a hash, adding one byte of data.  N must be a native
+hash size.
+*/
+template<unsigned N>
+typename HashTraits<N>::ResultType hash_round(typename HashTraits<N>::HashType result, uint8_t byte)
+{
+	constexpr typename HashTraits<N>::HashType prime = HashTraits<N>::prime;
+	return (result^byte)*prime;
+}
+
+/**
+Updates a previously computed hash by adding bytes to it.  N must be a native
+hash size.
+*/
+template<unsigned N>
+typename HashTraits<N>::ResultType hash_update(typename HashTraits<N>::HashType result, const void *data, std::size_t size)
+{
+	const uint8_t *ptr = static_cast<const uint8_t *>(data);
+	for(unsigned i=0; i<size; ++i)
+		result = hash_round<N>(result, *ptr++);
+	return result;
+}
+
+template<unsigned N>
+typename HashTraits<N>::ResultType hash_update(typename HashTraits<N>::HashType result, const std::string &str)
+{ return hash_update<N>(result, str.data(), str.size()); }
+
+// For some reason this causes an ambiguity error without the enable_if.
+template<unsigned N, typename T>
+typename std::enable_if<!std::is_same<T, std::string>::value, typename HashTraits<N>::ResultType>::type hash_update(typename HashTraits<N>::HashType result, const T &obj)
+{ return hash_update<N>(result, &obj, sizeof(obj)); }
 
 /**
 Manually folds a hash to a smaller size.
@@ -86,10 +118,7 @@ template<unsigned N>
 typename HashTraits<N>::ResultType hash(const void *data, std::size_t size)
 {
 	constexpr unsigned hash_bits = std::numeric_limits<typename HashTraits<N>::HashType>::digits;
-	constexpr typename HashTraits<N>::HashType prime = HashTraits<hash_bits>::prime;
-	typename HashTraits<N>::HashType result = HashTraits<hash_bits>::offset;
-	for(unsigned i=0; i<size; ++i)
-		result = (result^*(reinterpret_cast<const unsigned char *>(data)+i))*prime;
+	typename HashTraits<N>::HashType result = hash_update<hash_bits>(HashTraits<hash_bits>::offset, data, size);
 	if(HashTraits<N>::folded)
 		result = hash_fold<N>(result);
 	return result;
@@ -102,6 +131,14 @@ template<unsigned N>
 typename HashTraits<N>::ResultType hash(const std::string &str)
 { return hash<N>(str.data(), str.size()); }
 
+/**
+Convenience function to compute an N-bit hash of any object.  The entire object
+representation is hashed, including any padding bytes.
+*/
+template<unsigned N, typename T>
+typename HashTraits<N>::ResultType hash(const T &obj)
+{ return hash<N>(&obj, sizeof(obj)); }
+
 } // namespace Msp
 
 #endif