On Thu, Apr 7, 2016 at 2:28 PM, Barry Smith <[email protected]> wrote:
>
> We have code
>
> return (BT_idx = index/PETSC_BITS_PER_BYTE,
> BT_c = array[BT_idx],
> BT_mask = (char)(1 << index%PETSC_BITS_PER_BYTE),
> array[BT_idx] = (char)(BT_c | BT_mask),
> (char)(BT_c & BT_mask));
>
> inside
>
> petscbt.h
>
> the clang static code analyzer reports
>
> In file included from
> /sandbox/petsc/petsc.clone/include/petsc/private/matimpl.h:1233:
> /sandbox/petsc/petsc.clone/include/petscbt.h:85:36: warning: The result of
> the '<<' expression is undefined
> BT_mask = (char)(1 << index%PETSC_BITS_PER_BYTE),
> ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Is the code wrong/unnecessary or clang?
>
It looks right to me:
index%PETSC_BITS_PER_BYTE
gives the offset of this bit in the current byte.
1 << index%PETSC_BITS_PER_BYTE
Gives an int with a 1 at the offset'th bit, and then
we cast to a char.
I have no idea why clang complains.
Matt
> Thanks
>
>
--
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
