Warning generated in SNC C++ compiler by use of __sync_fetch_and_add

[Fernando Diaz <fdiaza@…>]

When compiling code that uses boost/shared_array.hpp in SNC C++ compiler, the following warning is generated:

../../SDKs/Boost/boost/smart_ptr/detail/sp_counted_base_sync.hpp(48,37): warning 68: integer conversion resulted in a change of sign

in this line:

return __sync_fetch_and_add( pw, -1 );

I've managed to fix the warning by replacing "sync_fetch_and_add" with "sync_fetch_and_sub", and changing the second argument from "-1" to "1". I've included a patch, hope it helps.

[Fernando Diaz <fdiaza@…>]

Proposed change to fix warning

[Peter Dimov]

This is a problem with SNC. The prototype of __sync_fetch_and_add is

type __sync_fetch_and_add (type *ptr, type value, ...)

i.e. the second argument should be the same type as the first, which, in shared_ptr's code, is sp_int32_t, a signed integer.

[Fernando Diaz <fdiaza@…>]

I see. In any case, am I correct in seeing

__sync_fetch_and_add( pw, -1 );

and

__sync_fetch_and_sub( pw, 1 );

as interchangeable? Because if the change is correct, but cannot be incorporated into boost, I could keep it on my side and reapply it each time boost is updated. Thanks!

[Peter Dimov]

They should be interchangeable, but the first one has already been tested and the replacement has not, so I'm a bit reluctant to change it unconditionally. Have you tried reporting this as a problem to the SNC folks? I hear that they're quite responsive. If they don't want to eliminate the warning, we could add __sync_fetch_and_sub in an #ifdef __SNC__.

[Peter Dimov]

I'm closing this as too old and probably no longer relevant. Please reopen if this is not the case.