chiark - git - mdw - mLib/blob - mem/growbuf.h

   1 /* -*-c-*-
   2  *
   3  * Grow a buffer if it's too small
   4  *
   5  * (c) 2024 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of the mLib utilities library.
  11  *
  12  * mLib is free software: you can redistribute it and/or modify it under
  13  * the terms of the GNU Library General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or (at
  15  * your option) any later version.
  16  *
  17  * mLib is distributed in the hope that it will be useful, but WITHOUT
  18  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  19  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
  20  * License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with mLib.  If not, write to the Free Software
  24  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
  25  * USA.
  26  */
  27
  28 #ifndef MLIB_GROWBUF_H
  29 #define MLIB_GROWBUF_H
  30
  31 #ifdef __cplusplus
  32   extern "C" {
  33 #endif
  34
  35 /*----- Header files ------------------------------------------------------*/
  36
  37 #include <assert.h>
  38 #include <stddef.h>
  39
  40 #ifndef MLIB_ALLOC_H
  41 #  include "alloc.h"
  42 #endif
  43
  44 /*----- Macros provided ---------------------------------------------------*/
  45
  46 /* --- @GROWBUF_LIMIT@ --- *
  47  *
  48  * Arguments:   @size_t granule@ = allocation granule
  49  *
  50  * Returns:     The largest number %$n$% such that the total size of %$n$%
  51  *              objects, each of size @granule@, can be represented in a
  52  *              @size_t@.
  53  */
  54
  55 #define GROWBUF_LIMIT(granule) (~(size_t)0/(granule))
  56
  57 /* --- @GROWBUF_SIZE@ --- *
  58  *
  59  * Arguments:   @size_t sz@ = the current size (updated)
  60  *              @size_t want@ = the desired minimum size
  61  *              @size_t init@ = a suitable initial size
  62  *              @size_t granule@ = the allocation granule size
  63  *
  64  * Returns:     ---
  65  *
  66  * Use:         On entry, @sz@ should be the current capacity of some buffer,
  67  *              in terms of objects of size @granule@, and @want@ a needed
  68  *              capacity, in the same terms, with @want > sz@; @init@ should
  69  *              be some suitable positive initial size, in case the current
  70  *              size is zero.  The macro updates @sz@ to be some suitable new
  71  *              positive size at least as large as @want@.
  72  */
  73
  74 #define GROWBUF_SIZE(sz, want, init, granule) do {                      \
  75   size_t _sz_ = (sz), _want_ = (want);                                  \
  76                                                                         \
  77   assert(_want_ < GROWBUF_LIMIT(granule)/2);                            \
  78   if (!_sz_) _sz_ = (init);                                             \
  79   while (_sz_ < _want_) _sz_ *= 2;                                      \
  80   (sz) = _sz_;                                                          \
  81 } while (0)
  82
  83 /* --- @GROWBUF_EXTEND@, @GROWBUF_REPLACE@ --- *
  84  *
  85  * Arguments:   @arena *a@ = pointer to an arena
  86  *              @type *buf@ = pointer to some buffer, possibly null (updated)
  87  *              @size_t sz@ = current buffer size (updated)
  88  *              @size_t want@ = desired minimum size
  89  *              @size_t init@ = a suitable initial size
  90  *              @size_t granule@ = the allocation granule size
  91  *
  92  * Returns:     ---
  93  *
  94  * Use:         On entry, @buf@ should be a pointer to a buffer, allocated
  95  *              from the arena @a@, with space for @sz@ objects of size
  96  *              @granule@; @buf@ may be null if @sz@ is zero.  On exit, @buf@
  97  *              and @sz@ will be updated to refer to a possibly different
  98  *              buffer, with space for at least @want@ objects (but certainly
  99  *              not smaller than before).
 100  *
 101  *              @GROWBUF_EXTEND@ preserves the contents of the buffer;
 102  *              @GROWBUF_REPLACE@ discards the existing contents.
 103  */
 104
 105 #define GROWBUF_EXTEND(a, buf, sz, want, init, granule) do {            \
 106   size_t _sz0 = (sz), _sz = _sz0, _want = (want), _gr = (granule);      \
 107   void *_p = (buf);                                                     \
 108   arena *_a = (a);                                                      \
 109                                                                         \
 110   if (_sz < _want) {                                                    \
 111     GROWBUF_SIZE(_sz, _want, init, _gr);                                \
 112     if (!_p) _p = x_alloc(_a, _sz*_gr);                                 \
 113     else _p = x_realloc(_a, _p, _sz*_gr, _sz0*_gr);                     \
 114     (buf) = _p; (sz) = _sz;                                             \
 115   }                                                                     \
 116 } while (0)
 117
 118 #define GROWBUF_REPLACE(a, buf, sz, want, init, granule) do {           \
 119   size_t _sz0 = (sz), _sz = _sz0, _want = (want), _gr = (granule);      \
 120   void *_p = (buf);                                                     \
 121   arena *_a = (a);                                                      \
 122                                                                         \
 123   if (_sz < _want) {                                                    \
 124     GROWBUF_SIZE(_sz, want, init, _gr);                                 \
 125     if (_p) x_free(_a, _p);                                             \
 126     _p = x_alloc(_a, _sz*_gr);                                          \
 127     (buf) = _p; (sz) = _sz;                                             \
 128   }                                                                     \
 129 } while (0)
 130
 131 /*----- That's all, folks -------------------------------------------------*/
 132
 133 #ifdef __cplusplus
 134   }
 135 #endif
 136
 137 #endif