@@@ man wip

[mLib] / mem / growbuf.h

/* -*-c-*-
 *
 * Grow a buffer if it's too small
 *
 * (c) 2024 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of the mLib utilities library.
 *
 * mLib is free software: you can redistribute it and/or modify it under
 * the terms of the GNU Library General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or (at
 * your option) any later version.
 *
 * mLib 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 Library General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with mLib.  If not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
 * USA.
 */

#ifndef MLIB_GROWBUF_H
#define MLIB_GROWBUF_H

#ifdef __cplusplus
  extern "C" {
#endif

/*----- Header files ------------------------------------------------------*/

#include <assert.h>
#include <stddef.h>

#ifndef MLIB_ALLOC_H
#  include "alloc.h"
#endif

/*----- Macros provided ---------------------------------------------------*/

/* --- @GROWBUF_LIMIT@ --- *
 *
 * Arguments:	@size_t granule@ = allocation granule
 *
 * Returns:	The largest number %$n$% such that the total size of %$n$%
 *		objects, each of size @granule@, can be represented in a
 *		@size_t@.
 */

#define GROWBUF_LIMIT(granule) (~(size_t)0/(granule))

/* --- @GROWBUF_SIZE@ --- *
 *
 * Arguments:	@size_t sz@ = the current size (updated)
 *		@size_t want@ = the desired minimum size
 *		@size_t init@ = a suitable initial size
 *		@size_t granule@ = the allocation granule size
 *
 * Returns:	---
 *
 * Use:		On entry, @sz@ should be the current capacity of some buffer,
 *		in terms of objects of size @granule@, and @want@ a needed
 *		capacity, in the same terms, with @want > sz@; @init@ should
 *		be some suitable positive initial size, in case the current
 *		size is zero.  The macro updates @sz@ to be some suitable new
 *		positive size at least as large as @want@.
 */

#define GROWBUF_SIZE(sz, want, init, granule) do {			\
  size_t _sz_ = (sz), _want_ = (want);					\
									\
  assert(_want_ < GROWBUF_LIMIT(granule)/2);				\
  if (!_sz_) _sz_ = (init);						\
  while (_sz_ < _want_) _sz_ *= 2;					\
  (sz) = _sz_;								\
} while (0)

/* --- @GROWBUF_EXTEND@, @GROWBUF_REPLACE@ --- *
 *
 * Arguments:	@arena *a@ = pointer to an arena
 *		@type *buf@ = pointer to some buffer, possibly null (updated)
 *		@size_t sz@ = current buffer size (updated)
 *		@size_t want@ = desired minimum size
 *		@size_t init@ = a suitable initial size
 *		@size_t granule@ = the allocation granule size
 *
 * Returns:	---
 *
 * Use:		On entry, @buf@ should be a pointer to a buffer, allocated
 *		from the arena @a@, with space for @sz@ objects of size
 *		@granule@; @buf@ may be null if @sz@ is zero.  On exit, @buf@
 *		and @sz@ will be updated to refer to a possibly different
 *		buffer, with space for at least @want@ objects (but certainly
 *		not smaller than before).
 *
 *		@GROWBUF_EXTEND@ preserves the contents of the buffer;
 *		@GROWBUF_REPLACE@ discards the existing contents.
 */

#define GROWBUF_EXTEND(a, buf, sz, want, init, granule) do {		\
  size_t _sz0 = (sz), _sz = _sz0, _want = (want), _gr = (granule);	\
  void *_p = (buf);							\
  arena *_a = (a);							\
									\
  if (_sz < _want) {							\
    GROWBUF_SIZE(_sz, _want, init, _gr);				\
    if (!_p) _p = x_alloc(_a, _sz*_gr);					\
    else _p = x_realloc(_a, _p, _sz*_gr, _sz0*_gr);			\
    (buf) = _p; (sz) = _sz;						\
  }									\
} while (0)

#define GROWBUF_REPLACE(a, buf, sz, want, init, granule) do {		\
  size_t _sz0 = (sz), _sz = _sz0, _want = (want), _gr = (granule);	\
  void *_p = (buf);							\
  arena *_a = (a);							\
									\
  if (_sz < _want) {							\
    GROWBUF_SIZE(_sz, want, init, _gr);					\
    if (_p) x_free(_a, _p);						\
    _p = x_alloc(_a, _sz*_gr);						\
    (buf) = _p; (sz) = _sz;						\
  }									\
} while (0)

/*----- That's all, folks -------------------------------------------------*/

#ifdef __cplusplus
  }
#endif

#endif