Hello. I would like to discuss a performance issue with boost::uuids::uuid operator ==. Let us consider the following program: --------------------------------------------------- #include <boost/uuid/uuid.hpp> #include <boost/uuid/uuid_generators.hpp> int main() { boost::uuids::uuid id1((boost::uuids::random_generator()())), id2((boost::uuids::random_generator()())); return id1 == id2; // we will consider this line } --------------------------------------------------- That is compiled with maximum optimizations the following way with Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.40219.01 for 80x86: cl -EHsc -Ox -GL -Ob2 -Oi -Fa -I..\3dparty\boost_1_48_0 m051.cpp boost uses the following comparison operator: inline bool operator==(uuid const& lhs, uuid const& rhs) /* throw() */ { return std::equal(lhs.begin(), lhs.end(), rhs.begin()); } which end up with the following code: lea edx, DWORD PTR _id2$[esp+92] lea ecx, DWORD PTR _id1$[esp+108] lea eax, DWORD PTR _id1$[esp+92] call ?_Equal@std@@YA_NPBE00@Z ; std::_Equal The whole story looks the following way (the code above plus std::_Equal call expansion): 0117C6AB lea edx,[esp+24h] 0117C6AF lea ecx,[esp+48h] 0117C6B3 lea eax,[esp+38h] 0117C6B7 call 01171000 01171000 push esi 01171001 mov esi,eax 01171003 sub ecx,esi 01171005 push edi 01171006 cmp ecx,4 01171009 jb 01171024 0117100B jmp 01171010 0117100D lea ecx,[ecx] 01171010 mov eax,dword ptr [esi] 01171012 cmp eax,dword ptr [edx] 01171014 jne 01171028 01171016 sub ecx,4 01171019 add edx,4 0117101C add esi,4 0117101F cmp ecx,4 01171022 jae 01171010 01171024 test ecx,ecx 01171026 je 01171073 01171028 movzx eax,byte ptr [esi] 0117102B movzx edi,byte ptr [edx] 0117102E sub eax,edi 01171030 jne 01171063 01171032 cmp ecx,1 01171035 jbe 01171073 01171037 movzx eax,byte ptr [esi+1] 0117103B movzx edi,byte ptr [edx+1] 0117103F sub eax,edi 01171041 jne 01171063 01171043 cmp ecx,2 01171046 jbe 01171073 01171048 movzx eax,byte ptr [esi+2] 0117104C movzx edi,byte ptr [edx+2] 01171050 sub eax,edi 01171052 jne 01171063 01171054 cmp ecx,3 01171057 jbe 01171073 01171059 movzx eax,byte ptr [esi+3] 0117105D movzx ecx,byte ptr [edx+3] 01171061 sub eax,ecx 01171063 sar eax,1Fh 01171066 or eax,1 01171069 xor edx,edx 0117106B test eax,eax 0117106D pop edi 0117106E sete al 01171071 pop esi 01171072 ret 01171073 xor eax,eax 01171075 xor edx,edx 01171077 test eax,eax 01171079 pop edi 0117107A sete al 0117107D pop esi 0117107E ret I do understand that the boost::uuids::uuid implementation is conceptually correct and inoculate the best programming practices. But the following equivalent is too much faster (you may probably want to ensure a proper alignment for some processor architectures or even get even faster 64-bit version): inline bool comp(const boost::uuids::uuid& l, const boost::uuids::uuid& r) { return *reinterpret_cast<const uint32_t*>(l.data) == *reinterpret_cast<const uint32_t*>(r.data) && *reinterpret_cast<const uint32_t*>(l.data+4) == *reinterpret_cast<const uint32_t*>(r.data+4) && *reinterpret_cast<const uint32_t*>(l.data+8) == *reinterpret_cast<const uint32_t*>(r.data+8) && *reinterpret_cast<const uint32_t*>(l.data+12) == *reinterpret_cast<const uint32_t*>(r.data+12); } the assembler output is: mov ecx, DWORD PTR _id1$[esp+92] cmp ecx, DWORD PTR _id2$[esp+92] jne SHORT $LN37@main mov edx, DWORD PTR _id1$[esp+96] cmp edx, DWORD PTR _id2$[esp+96] jne SHORT $LN37@main mov eax, DWORD PTR _id1$[esp+100] cmp eax, DWORD PTR _id2$[esp+100] jne SHORT $LN37@main mov ecx, DWORD PTR _id1$[esp+104] cmp ecx, DWORD PTR _id2$[esp+104] jne SHORT $LN37@main mov eax, 1 jmp SHORT $LN40@main $LN37@main: xor eax, eax $LN40@main: movzx eax, al that the question comes: is boost supposed to be used in commercial applications or it is just a testing area for some concepts? You have probably never thought of the fact that Debug (unoptimized configurations) are sometimes just unusable with such approach on real (big) data. If you are interested you may want to compile the program above this way and see the resulting code: cl -EHsc -Zi -Fa -I..\3dparty\boost_1_48_0 m051.cpp Thank you in advance for your considerations. -- Michael Kochetkov