SL-19110 Fast hashing classes for use in place of the slow LLMD5, where speed matters. (#64)

This commit adds the HBXX64 and HBXX128 classes for use as a drop-in
replacement for the slow LLMD5 hashing class, where speed matters and
backward compatibility (with standard hashing algorithms) and/or
cryptographic hashing qualities are not required.
It also replaces LLMD5 with HBXX* in a few existing hot (well, ok, just
"warm" for some) paths meeting the above requirements, while paving the way for
future use cases, such as in the DRTVWR-559 and sibling branches where the slow
LLMD5 is used (e.g. to hash materials and vertex buffer cache entries), and
could be use such a (way) faster algorithm with very significant benefits and
no negative impact.

Here is the comment I added in indra/llcommon/hbxx.h:

// HBXXH* classes are to be used where speed matters and cryptographic quality
// is not required (no "one-way" guarantee, though they are likely not worst in
// this respect than MD5 which got busted and is now considered too weak). The
// xxHash code they are built upon is vectorized and about 50 times faster than
// MD5. A 64 bits hash class is also provided for when 128 bits of entropy are
// not needed. The hashes collision rate is similar to MD5's.
// See https://github.com/Cyan4973/xxHash#readme for details.

1 files changed, 8 insertions, 20 deletions

diff --git a/indra/llcommon/lluuid.cpp b/indra/llcommon/lluuid.cpp
index acce8366ea..8ff6c45760 100644
--- a/indra/llcommon/lluuid.cpp
+++ b/indra/llcommon/lluuid.cpp
@@ -40,11 +40,11 @@
 #include "lluuid.h"
 #include "llerror.h"
 #include "llrand.h"
-#include "llmd5.h"
 #include "llstring.h"
 #include "lltimer.h"
 #include "llthread.h"
 #include "llmutex.h"
+#include "hbxxh.h"
 
 const LLUUID LLUUID::null;
 const LLTransactionID LLTransactionID::tnull;
@@ -402,11 +402,9 @@ LLUUID LLUUID::operator^(const LLUUID& rhs) const
 
 void LLUUID::combine(const LLUUID& other, LLUUID& result) const
 {
-	LLMD5 md5_uuid;
-	md5_uuid.update((unsigned char*)mData, 16);
-	md5_uuid.update((unsigned char*)other.mData, 16);
-	md5_uuid.finalize();
-	md5_uuid.raw_digest(result.mData);
+	HBXXH128 hash((const void*)mData, 16, false);	// false = do not finalize
+	hash.update((const void*)other.mData, 16);
+	hash.digest(result);
 }
 
 LLUUID LLUUID::combine(const LLUUID &other) const
@@ -857,17 +855,12 @@ void LLUUID::generate()
 	tmp >>= 8;
 	mData[8] = (unsigned char) tmp;
 
-	LLMD5 md5_uuid;
-	
-	md5_uuid.update(mData,16);
-	md5_uuid.finalize();
-	md5_uuid.raw_digest(mData);
+	HBXXH128::digest(*this, (const void*)mData, 16);
 }
 
 void LLUUID::generate(const std::string& hash_string)
 {
-	LLMD5 md5_uuid((U8*)hash_string.c_str());
-	md5_uuid.raw_digest(mData);
+	HBXXH128::digest(*this, hash_string);
 }
 
 U32 LLUUID::getRandomSeed()
@@ -885,13 +878,8 @@ U32 LLUUID::getRandomSeed()
    seed[7]=(unsigned char)(pid);
    getSystemTime((uuid_time_t *)(&seed[8]));
 
-   LLMD5 md5_seed;
-	
-   md5_seed.update(seed,16);
-   md5_seed.finalize();
-   md5_seed.raw_digest(seed);
-   
-   return(*(U32 *)seed);
+   U64 seed64 = HBXXH64((const void*)seed, 16).digest();
+   return U32(seed64) ^ U32(seed64 >> 32);
 }
 
 BOOL LLUUID::parseUUID(const std::string& buf, LLUUID* value)