From 1eb2b23f4b254052924b198d446c052df9ca3124 Mon Sep 17 00:00:00 2001
From: Henri Beauchamp <sldevel@users.noreply.github.com>
Date: Tue, 7 Feb 2023 13:51:53 +0100
Subject: SL-19159 Faster LLUUID and LLMaterialID hashing for std and boost
 containers keys (#70)

LLUUID and LLMaterialID already have an excellent entropy and value dispersion; there is therefore strictly no need to further (slowly) hash their value for use with std and boost libraries containers.

This commit adds a trivial getDigest64() method to both LLUUID and LLMaterialID (which simply returns the XOR of the two 64 bits long words their value is made of), and uses it in std::hash and hash_value() specializations for use with containers.
---
 indra/llcommon/lluuid.cpp |  2 +-
 indra/llcommon/lluuid.h   | 50 ++++++++++++++++++++---------------------------
 2 files changed, 22 insertions(+), 30 deletions(-)

(limited to 'indra/llcommon')

diff --git a/indra/llcommon/lluuid.cpp b/indra/llcommon/lluuid.cpp
index 8ff6c45760..aa8045e6ab 100644
--- a/indra/llcommon/lluuid.cpp
+++ b/indra/llcommon/lluuid.cpp
@@ -878,7 +878,7 @@ U32 LLUUID::getRandomSeed()
    seed[7]=(unsigned char)(pid);
    getSystemTime((uuid_time_t *)(&seed[8]));
 
-   U64 seed64 = HBXXH64((const void*)seed, 16).digest();
+   U64 seed64 = HBXXH64::digest((const void*)seed, 16);
    return U32(seed64) ^ U32(seed64 >> 32);
 }
 
diff --git a/indra/llcommon/lluuid.h b/indra/llcommon/lluuid.h
index 86a396ab06..2c36a1d222 100644
--- a/indra/llcommon/lluuid.h
+++ b/indra/llcommon/lluuid.h
@@ -119,6 +119,14 @@ public:
 	U16 getCRC16() const;
 	U32 getCRC32() const;
 
+	// Returns a 64 bits digest of the UUID, by XORing its two 64 bits long
+	// words. HB
+	inline U64 getDigest64() const
+	{
+		U64* tmp = (U64*)mData;
+		return tmp[0] ^ tmp[1];
+	}
+
 	static BOOL validate(const std::string& in_string); // Validate that the UUID string is legal.
 
 	static const LLUUID null;
@@ -165,36 +173,20 @@ public:
 	LLAssetID makeAssetID(const LLUUID& session) const;
 };
 
-// Generate a hash of an LLUUID object using the boost hash templates. 
-template <>
-struct boost::hash<LLUUID>
-{
-    typedef LLUUID argument_type;
-    typedef std::size_t result_type;
-    result_type operator()(argument_type const& s) const
-    {
-        result_type seed(0);
-
-        for (S32 i = 0; i < UUID_BYTES; ++i)
-        {
-            boost::hash_combine(seed, s.mData[i]);
-        }
-
-        return seed;
-    }
-};
-
-// Adapt boost hash to std hash
+// std::hash implementation for LLUUID
 namespace std
 {
-    template<> struct hash<LLUUID>
-    {
-        std::size_t operator()(LLUUID const& s) const noexcept
-        {
-            return boost::hash<LLUUID>()(s);
-        }
-    };
+	template<> struct hash<LLUUID>
+	{
+		inline size_t operator()(const LLUUID& id) const noexcept
+		{
+			return (size_t)id.getDigest64();
+		}
+	};
 }
-#endif
-
 
+// For use with boost containers.
+inline size_t hash_value(const LLUUID& id) noexcept
+{
+	return (size_t)id.getDigest64();
+}
-- 
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