Re: Benchmarking temporary Lisp objects [Was: Re: [RFC] temporary Lisp_Strings]

[Dmitry Antipov <dmantipov@yandex.ru>]

On 09/04/2014 05:37 PM, Dmitry Antipov wrote:

> Thanks to Paul, there is a C99-compilant solution:

As for the vectors, I don't know how to use VLAs in the way similar
to alloca in the following attempt:

INLINE Lisp_Object
local_vector_init (uintptr_t addr, ptrdiff_t length, Lisp_Object init)
{
   ptrdiff_t i;
   struct Lisp_Vector *v = (struct Lisp_Vector *) addr;

   v->header.size = length;
   for (i = 0; i < length; i++)
     v->contents[i] = init;
   return make_lisp_ptr (v, Lisp_Vectorlike);
}

#define local_vector(obj, length, init)                                    \
   (MAX_ALLOCA < (length) * word_size + header_size                         \
    ? Fmake_vector (make_number (length), (init))                           \
    : (obj = XIL ((uintptr_t) alloca ((length) * word_size + header_size)), \
       local_vector_init ((uintptr_t) XLI (obj), (length), (init))))

Users are expected to call:

Lisp_Object obj = local_vector (obj, 10, Qnil);

Somewhat similar may be implemented for strings.

Dmitry