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, 7 insertions, 12 deletions

diff --git a/indra/llprimitive/llmodel.cpp b/indra/llprimitive/llmodel.cpp
index 206142fdd5..52fb8e3802 100644
--- a/indra/llprimitive/llmodel.cpp
+++ b/indra/llprimitive/llmodel.cpp
@@ -31,7 +31,7 @@
 #include "llconvexdecomposition.h"
 #include "llsdserialize.h"
 #include "llvector4a.h"
-#include "llmd5.h"
+#include "hbxxh.h"
 
 #ifdef LL_USESYSTEMLIBS
 # include <zlib.h>
@@ -1564,7 +1564,7 @@ LLSD LLMeshSkinInfo::asLLSD(bool include_joints, bool lock_scale_if_joint_positi
 void LLMeshSkinInfo::updateHash()
 {
     //  get hash of data relevant to render batches
-    LLMD5 hash;
+    HBXXH64 hash;
 
     //mJointNames
     for (auto& name : mJointNames)
@@ -1573,24 +1573,19 @@ void LLMeshSkinInfo::updateHash()
     }
     
     //mJointNums 
-    hash.update((U8*)&(mJointNums[0]), sizeof(S32) * mJointNums.size());
+    hash.update((const void*)mJointNums.data(), sizeof(S32) * mJointNums.size());
     
     //mInvBindMatrix
     F32* src = mInvBindMatrix[0].getF32ptr();
     
-    for (int i = 0; i < mInvBindMatrix.size() * 16; ++i)
+    for (size_t i = 0, count = mInvBindMatrix.size() * 16; i < count; ++i)
     {
         S32 t = llround(src[i] * 10000.f);
-        hash.update((U8*)&t, sizeof(S32));
+        hash.update((const void*)&t, sizeof(S32));
     }
-    //hash.update((U8*)&(mInvBindMatrix[0]), sizeof(LLMatrix4a) * mInvBindMatrix.size());
+    //hash.update((const void*)mInvBindMatrix.data(), sizeof(LLMatrix4a) * mInvBindMatrix.size());
 
-    hash.finalize();
-
-    U64 digest[2];
-    hash.raw_digest((U8*) digest);
-
-    mHash = digest[0];
+    mHash = hash.digest();
 }
 
 U32 LLMeshSkinInfo::sizeBytes() const