Re: [PATCH] Reduce memory size of tsearch red-black tree.

[Florian Weimer <fweimer at redhat dot com>]

On 08/15/2016 07:40 PM, Adhemerval Zanella wrote:

> > +/* Assume malloc returns naturally aligned (alignof (max_align_t))
> > +   pointers so we can use the low bits to store some extra info.  This
> > +   works for the left/right node pointers since they are not user
> > +   visible and always allocated by malloc.  The user provides the key
> > +   pointer and so that can point anywhere and doesn't have to be
> > +   aligned.  */
> > +#define CAN_USE_MALLOC_LOW_BIT 1
> > +
> > +#ifndef CAN_USE_MALLOC_LOW_BIT
>
> Why not enforce alignment with memalign/posix_memalign/aligned_alloc and
> drop CAN_USE_MALLOC_LOW_BIT?

We just got rid of the need to interpose __libc_memalign along with an 
external malloc.

tsearch is part of older standards as well, and I don't think these have 
an aligned allocation interface.  I don't think the namespace issue can 
be resolved easily.

Florian