/*

Copyright (C) 2008-2015 Jaroslav Hajek

This file is part of Octave.

Octave is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 3 of the License, or (at your
option) any later version.

Octave is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with Octave; see the file COPYING.  If not, see
<http://www.gnu.org/licenses/>.

*/

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include <iostream>

#include "lo-error.h"
#include "oct-locbuf.h"

// FIXME: Maybe we should querying for available physical memory?

#ifndef OCTAVE_LOCBUF_CHUNKSIZE_MB
#  define OCTAVE_LOCBUF_CHUNKSIZE_MB 32
#endif

// Each chunk will be at least this big.

const size_t octave_chunk_buffer::chunk_size =
  static_cast<size_t> (OCTAVE_LOCBUF_CHUNKSIZE_MB) << 20;

char *octave_chunk_buffer::top = 0;
char *octave_chunk_buffer::chunk = 0;
size_t octave_chunk_buffer::left = 0;
size_t octave_chunk_buffer::active = 0;

octave_chunk_buffer::octave_chunk_buffer (size_t size) : cnk (0), dat (0)
{
  // Alignment mask. The size of double or long int, whichever is
  // greater.  All data will be aligned to this size.  If it's not
  // enough for a type, that type should not be declared as POD.

  static const size_t align_mask = (sizeof (long) < sizeof (double)
                                    ? sizeof (double)
                                    : sizeof (long)) - 1;

  active++;

  if (! size)
    return;

  // Align size. Note that size_t is unsigned, so size-1 must correctly
  // wrap around.

  size = ((size - 1) | align_mask) + 1;

  if (size > left)
    {
      // Big buffers (> 1/8 chunk) will be allocated as stand-alone and
      // won't disrupt the chain.

      if (size > chunk_size >> 3)
        {
          // Use new [] to get std::bad_alloc if out of memory.

          dat = new char [size];
          return;
        }

      dat = new char [chunk_size];
      chunk = top = dat;
      left = chunk_size;
    }

  // Now allocate memory from the chunk and update state.

  cnk = chunk;
  dat = top;
  left -= size;
  top += size;
}

octave_chunk_buffer::~octave_chunk_buffer (void)
{
  active--;

  if (cnk == chunk)
    {
      // Our chunk is still the active one.  Just restore the state.

      left += top - dat;
      top = dat;
    }
  else
    {
      if (cnk)
        {
          // Responsible for deletion.

          delete [] chunk;
          chunk = cnk;
          top = dat;

          // FIXME: the following calcuation of remaining data will
          //        only work if each chunk has the same chunk_size.

          left = chunk_size - (dat - cnk);
        }
      else
        {
          // We were a stand-alone buffer.

          delete [] dat;
        }
    }
}

// Clear the final chunk of allocated memory.

void
octave_chunk_buffer::clear (void)
{
  if (active == 0)
    {
      delete [] chunk;
      chunk = 0;
      top = 0;
      left = 0;
    }
  else
    {
      // FIXME: Doesn't this situation represent a programming error of
      // some kind?  If so, maybe this should be a fatal error?

      (*current_liboctave_warning_with_id_handler)
        ("Octave:local-buffer-inconsistency",
         "octave_chunk_buffer::clear: %d active allocations remain!",
         active);
    }
}