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

From: Dmitry Antipov
Subject: Re: Benchmarking temporary Lisp objects [Was: Re: [RFC] temporary Lisp_Strings]
Date: Thu, 04 Sep 2014 18:46:54 +0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0

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.


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