I assume that time_duration is implemented as an integer. Some values of this integer are then reserved for special values like not_a_date_time. this can be seen here: https://github.com/boostorg/date_time/blob/develop/include/boost/date_time/i... this should have the consequence that when studying the assembler code for comparing two time_durations, all that happens is the assembler code of "less than compare" for integer type. if additional comparisons and branchings take place, then I assume the code is not meeting the design criteria of being optimized. Well... this is what I did, copy paste this code to justcompare.cpp: #include <boost/date_time/posix_time/ptime.hpp> using namespace boost::posix_time; bool compare_time_duration(time_duration a, time_duration b) { return a < b; } bool compare_int(int a, int b) { return a < b; } EOF g++ -Wall -O2 -c justcompare.cpp objdump -S --demangle justcompare.o justcompare.o: file format elf64-x86-64 Disassembly of section .text: 0000000000000000 <compare_time_duration(boost::posix_time::time_duration, boost::posix_time::time_duration)>: 0: 48 8b 17 mov (%rdi),%rdx 3: 48 b9 ff ff ff ff ff movabs $0x7fffffffffffffff,%rcx a: ff ff 7f d: 48 8d 04 0a lea (%rdx,%rcx,1),%rax 11: 48 83 f8 fd cmp $0xfffffffffffffffd,%rax 15: 77 29 ja 40 17: 48 bf fe ff ff ff ff movabs $0x7ffffffffffffffe,%rdi 1e: ff ff 7f 21: 31 c0 xor %eax,%eax 23: 48 39 fa cmp %rdi,%rdx 26: 74 60 je 88 28: 48 8b 36 mov (%rsi),%rsi 2b: 48 01 f1 add %rsi,%rcx 2e: 48 83 f9 fd cmp $0xfffffffffffffffd,%rcx 32: 77 20 ja 54 34: 48 39 fe cmp %rdi,%rsi 37: 74 0a je 43 39: 48 39 f2 cmp %rsi,%rdx 3c: 0f 9c c0 setl %al 3f: c3 retq 40: 48 8b 36 mov (%rsi),%rsi 43: 48 b9 fe ff ff ff ff movabs $0x7ffffffffffffffe,%rcx 4a: ff ff 7f 4d: 31 c0 xor %eax,%eax 4f: 48 39 ce cmp %rcx,%rsi 52: 74 3c je 90 54: 48 bf 00 00 00 00 00 movabs $0x8000000000000000,%rdi 5b: 00 00 80 5e: 48 39 fa cmp %rdi,%rdx 61: 74 35 je 98 63: 48 b9 ff ff ff ff ff movabs $0x7fffffffffffffff,%rcx 6a: ff ff 7f 6d: 48 39 ce cmp %rcx,%rsi 70: 0f 94 c0 sete %al 73: 48 39 ca cmp %rcx,%rdx 76: 41 0f 95 c0 setne %r8b 7a: 44 20 c0 and %r8b,%al 7d: 74 21 je a0 7f: f3 c3 repz retq 81: 0f 1f 80 00 00 00 00 nopl 0x0(%rax) 88: f3 c3 repz retq 8a: 66 0f 1f 44 00 00 nopw 0x0(%rax,%rax,1) 90: f3 c3 repz retq 92: 66 0f 1f 44 00 00 nopw 0x0(%rax,%rax,1) 98: 48 39 d6 cmp %rdx,%rsi 9b: 0f 95 c0 setne %al 9e: c3 retq 9f: 90 nop a0: 48 39 ca cmp %rcx,%rdx a3: 74 da je 7f a5: 48 39 fe cmp %rdi,%rsi a8: 75 8f jne 39 aa: f3 c3 repz retq ac: 0f 1f 40 00 nopl 0x0(%rax) 00000000000000b0 <compare_int(int, int)>: b0: 39 f7 cmp %esi,%edi b2: 0f 9c c0 setl %al b5: c3 retq (i removed the verbose jump target strings from the output to make the email readable) see the difference between compare_time_duration and compare_int... I have a bad feeling in my stomach... sorry, something is going very wrong here :-) cya erik