Struct packing with MSVC about libosmium

[alex85k]

Yes, the error seems to vanish!
(however, you'll need to change initializer and getter/setter in a correct way)

[DennisOSRM]

thanks for providing the bitfield packing link, @joto

[alex85k]

The is a second alignment error:
D:\build_d\libosmium2\include\osmium/osm/changeset.hpp(307): error C2338: Class osmium::Changeset has wrong size to be aligned properly! [D:\build_d\libosmium2\build-cmake\examples\osmium_serdump.vcxproj]
Others seems to compile for now...

[joto]

I have committed a change that might fix this issue.

For the alignment error in changeset.hpp: Can you check adding string_size_type m_padding; after line 69?

[alex85k]

I have committed a change that might fix this issue.

Yes, that helped!

For the alignment error in changeset.hpp: Can you check adding string_size_type m_padding; after line 69?

This time it do not help :)
https://github.com/alex85k/libosmium/tree/msvc-v3

[joto]

@alex85k: Can you somehow try to find out how the Changeset class is layed out? Maybe there is some kind of debugging option for the MSVC compiler to check.
All the internal fields should be uint32_t or int32_t, except the last one which is int16_t. Adding up the 8 bytes from class Item and 38 bytes from class Changeset should result in sizeof(Changeset) == 48 which it is with GCC and clang.

[alex85k]

I'll try...

[alex85k]

sizeof(osmium::Changeset) == 52. O_O
Investigating...

[alex85k]

MinGW 64 bit:

sizeof(Item)             =8
sizeof(osmium::Timestamp)=4
sizeof(osmium::Timestamp)=4
sizeof(osmium::Box)      =16
sizeof(changeset_id_type)=4
sizeof(user_id_type )    =4
sizeof(string_size_type )=2
sizeof(num_changes_type) =4
sizeof(osmium::Changeset)=48

MSVC:

sizeof(Item)             =8
sizeof(osmium::Timestamp)=4
sizeof(osmium::Timestamp)=4
sizeof(osmium::Box)      =16
sizeof(changeset_id_type)=4
sizeof(user_id_type )    =4
sizeof(string_size_type )=2
sizeof(num_changes_type) =4
sizeof(osmium::Changeset)=52

Alignment...

[alex85k]

Even setting field to static

    static osmium::Timestamp m_created_at;
        static osmium::Timestamp m_closed_at;
        static osmium::Box       m_bounds;
        static changeset_id_type m_id;
        static num_changes_type  m_num_changes;
        static user_id_type      m_uid;
        static string_size_type  m_user_size;

gives sizeof(osmium::Changeset)=12.

[alex85k]

The reason: osmium::totally_ordered<Changeset> added 4 bytes!
Gr-r-r.. MS tricks us again!
http://social.msdn.microsoft.com/Forums/vstudio/en-US/504c6598-6076-4acf-96b6-e6acb475d302/vc-multiple-inheritance-empty-base-classes-bloats-object-size

[alex85k]

And this:
http://stackoverflow.com/questions/12701469/why-empty-base-class-optimization-is-not-working

We'll have size increasing also for NodeRef, OsmObject, UnidirectedSegment...

[alex85k]

I have added 4 bytes to Changeset to have at least 56 bytes (%8==0) instead of 48.
Do not know any better solution...

[alex85k]

Your solution is a little bit radical... But working :)