Implement hash function for rapidjson values

1 files changed, 95 insertions, 0 deletions

diff --git a/rapidjsonwrapper.h b/rapidjsonwrapper.h
index 18e6bd8f..cce07f9e 100644
--- a/rapidjsonwrapper.h
+++ b/rapidjsonwrapper.h
@@ -51,6 +51,101 @@ struct ParseException : public std::runtime_error, public rapidjson::ParseResult
 #include "rapidjson/writer.h"
 #include "rapidjson/prettywriter.h"
 
+
+
+inline size_t combine(size_t seed, size_t h) noexcept
+{
+	seed ^= h + 0x9e3779b9 + (seed << 6U) + (seed >> 2U);
+	return seed;
+}
+
+
+inline size_t HashBytes(const void* const ptr, const size_t len)
+{
+	// Taken from https://stackoverflow.com/questions/34597260/stdhash-value-on-char-value-and-not-on-memory-address
+	const char* cdata = static_cast<const char *>(ptr);
+	uint64_t acc = 0;
+	for (rapidjson::SizeType i = 0; i < len; ++i)
+	{
+		const size_t next = cdata[i];
+		acc = (acc ^ next) * 1099511628211;
+	}
+	return acc;
+}
+
+
+static uint64_t HashRapidValue(const rapidjson::Value& val)
+{
+	const auto type = static_cast<std::size_t>(val.GetType());
+	switch (val.GetType())
+	{
+		case rapidjson::kNullType:
+		case rapidjson::kFalseType:
+		{
+			return combine(type, 0);
+		}
+		case rapidjson::kObjectType:
+		{
+			auto seed = combine(type, val.MemberCount());
+			for (const auto& element : val.GetObject())
+			{
+				const auto h = HashBytes(element.name.GetString(), element.name.GetStringLength());
+				seed = combine(seed, h);
+				seed = combine(seed, HashRapidValue(element.value));
+			}
+			return seed;
+		}
+		case rapidjson::kArrayType:
+		{
+			auto seed = combine(type, val.Size());
+			for (const auto& element : val.GetArray())
+			{
+				seed = combine(seed, HashRapidValue(element));
+			}
+			return seed;
+		}
+		case rapidjson::kStringType:
+		{
+			return combine(type, HashBytes(val.GetString(), val.GetStringLength()));
+		}
+		case rapidjson::kTrueType:
+		{
+			return combine(type, 1);
+		}
+		case rapidjson::kNumberType:
+		{
+			size_t h;
+			if (val.IsDouble())
+			{
+				const double dVal = val.GetDouble();
+				h = HashBytes(&dVal, sizeof(dVal));
+			}
+			else if (val.IsInt())
+			{
+				h = static_cast<size_t>(val.GetInt());
+			}
+			else if (val.IsInt64())
+			{
+				h = static_cast<size_t>(val.GetUint64());
+			}
+			else if (val.IsUint())
+			{
+				h = static_cast<size_t>(val.GetUint());
+			}
+			else
+			{
+				h = val.GetUint64();
+			}
+			return combine(type, h);
+		}
+
+		default:
+			RAPIDJSON_ASSERT(false);
+			return 0;
+	}
+}
+
+
 #if defined(__GNUC__) && __GNUC__ >= 8
 	#pragma GCC diagnostic pop
 #endif