prefer memcpy to cast of unaligned pointer (#51)

include/orc/memory.hpp

@@ -45,6 +45,16 @@ decltype(auto) make_leaky(Args&&... args) {
 #endif
 }
 
+/**************************************************************************************************/
+// Useful for reading integer values (that otherwise need to be aligned) from unaligned memory. The
+// typical solution is to use memcpy and let the compiler optimize it further.
+template <class Integer>
+Integer unaligned_read(const void* p) {
+    Integer result{Integer()};
+    std::memcpy(&result, p, sizeof(result));
+    return result;
+}
+
 /**************************************************************************************************/
 
 } // namespace orc

src/hash.cpp

@@ -7,6 +7,9 @@
 // identity
 #include "orc/hash.hpp"
 
+// application
+#include "orc/memory.hpp"
+
 /**************************************************************************************************/
 
 namespace {
@@ -37,7 +40,9 @@ inline uint64_t rotl64(uint64_t x, int8_t r) { return (x << r) | (x >> (64 - r))
 
 /**************************************************************************************************/
 
-FORCE_INLINE uint64_t getblock64(const uint64_t* p, int i) { return p[i]; }
+FORCE_INLINE std::uint64_t getblock64(const uint64_t* p, int i) {
+    return orc::unaligned_read<std::uint64_t>(p + i);
+}
 
 /**************************************************************************************************/
 

src/string_pool.cpp

@@ -32,9 +32,7 @@ namespace {
 
 /**************************************************************************************************/
 
-std::size_t string_view_hash(std::string_view s) {
-    return orc::murmur3_64(s.data(), s.length());
-}
+std::size_t string_view_hash(std::string_view s) { return orc::murmur3_64(s.data(), s.length()); }
 
 /**************************************************************************************************/
 
@@ -85,19 +83,16 @@ struct pool {
 std::size_t pool_string::get_size(const char* d) {
     assert(d);
     const void* bytes = d - sizeof(std::uint32_t) - sizeof(std::size_t);
-    std::uint32_t s;
-    std::memcpy(&s, bytes, sizeof(s)); // not aligned - need to use memcpy
-    assert(s > 0);                     // required, else should have been _data == nullptr
-    assert(s < 100000);                // sanity check
+    std::uint32_t s = orc::unaligned_read<std::uint32_t>(bytes);
+    assert(s > 0);      // required, else should have been _data == nullptr
+    assert(s < 100000); // sanity check
     return s;
 }
 
 std::size_t pool_string::get_hash(const char* d) {
     assert(d);
     const void* bytes = d - sizeof(std::size_t);
-    std::size_t h;
-    std::memcpy(&h, bytes, sizeof(h)); // not aligned -- need to use memcpy
-    return h;
+    return orc::unaligned_read<std::size_t>(bytes);
 }
 
 pool_string empool(std::string_view src) {
@@ -106,7 +101,8 @@ pool_string empool(std::string_view src) {
     // default_view would be returned.)
     if (src.empty()) return pool_string(nullptr);
 
-    static decltype(auto) keys = orc::make_leaky<tbb::concurrent_unordered_map<size_t, const char*>>();
+    static decltype(auto) keys =
+        orc::make_leaky<tbb::concurrent_unordered_map<size_t, const char*>>();
 
     const std::size_t h = string_view_hash(src);