gnulib/import/malloca.h

   1 /* Safe automatic memory allocation.
   2    Copyright (C) 2003-2007, 2009-2016 Free Software Foundation, Inc.
   3    Written by Bruno Haible <bruno@clisp.org>, 2003.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3, or (at your option)
   8    any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program; if not, see <http://www.gnu.org/licenses/>.  */
  17
  18 #ifndef _MALLOCA_H
  19 #define _MALLOCA_H
  20
  21 #include <alloca.h>
  22 #include <stddef.h>
  23 #include <stdlib.h>
  24
  25
  26 #ifdef __cplusplus
  27 extern "C" {
  28 #endif
  29
  30
  31 /* safe_alloca(N) is equivalent to alloca(N) when it is safe to call
  32    alloca(N); otherwise it returns NULL.  It either returns N bytes of
  33    memory allocated on the stack, that lasts until the function returns,
  34    or NULL.
  35    Use of safe_alloca should be avoided:
  36      - inside arguments of function calls - undefined behaviour,
  37      - in inline functions - the allocation may actually last until the
  38        calling function returns.
  39 */
  40 #if HAVE_ALLOCA
  41 /* The OS usually guarantees only one guard page at the bottom of the stack,
  42    and a page size can be as small as 4096 bytes.  So we cannot safely
  43    allocate anything larger than 4096 bytes.  Also care for the possibility
  44    of a few compiler-allocated temporary stack slots.
  45    This must be a macro, not a function.  */
  46 # define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL)
  47 #else
  48 # define safe_alloca(N) ((void) (N), NULL)
  49 #endif
  50
  51 /* malloca(N) is a safe variant of alloca(N).  It allocates N bytes of
  52    memory allocated on the stack, that must be freed using freea() before
  53    the function returns.  Upon failure, it returns NULL.  */
  54 #if HAVE_ALLOCA
  55 # define malloca(N) \
  56   ((N) < 4032 - sa_increment                                        \
  57    ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \
  58    : mmalloca (N))
  59 #else
  60 # define malloca(N) \
  61   mmalloca (N)
  62 #endif
  63 extern void * mmalloca (size_t n);
  64
  65 /* Free a block of memory allocated through malloca().  */
  66 #if HAVE_ALLOCA
  67 extern void freea (void *p);
  68 #else
  69 # define freea free
  70 #endif
  71
  72 /* nmalloca(N,S) is an overflow-safe variant of malloca (N * S).
  73    It allocates an array of N objects, each with S bytes of memory,
  74    on the stack.  S must be positive and N must be nonnegative.
  75    The array must be freed using freea() before the function returns.  */
  76 #if 1
  77 /* Cf. the definition of xalloc_oversized.  */
  78 # define nmalloca(n, s) \
  79     ((n) > (size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) \
  80      ? NULL \
  81      : malloca ((n) * (s)))
  82 #else
  83 extern void * nmalloca (size_t n, size_t s);
  84 #endif
  85
  86
  87 #ifdef __cplusplus
  88 }
  89 #endif
  90
  91
  92 /* ------------------- Auxiliary, non-public definitions ------------------- */
  93
  94 /* Determine the alignment of a type at compile time.  */
  95 #if defined __GNUC__ || defined __IBM__ALIGNOF__
  96 # define sa_alignof __alignof__
  97 #elif defined __cplusplus
  98   template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
  99 # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
 100 #elif defined __hpux
 101   /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
 102      values.  */
 103 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
 104 #elif defined _AIX
 105   /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof
 106      values.  */
 107 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
 108 #else
 109 # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
 110 #endif
 111
 112 enum
 113 {
 114 /* The desired alignment of memory allocations is the maximum alignment
 115    among all elementary types.  */
 116   sa_alignment_long = sa_alignof (long),
 117   sa_alignment_double = sa_alignof (double),
 118 #if HAVE_LONG_LONG_INT
 119   sa_alignment_longlong = sa_alignof (long long),
 120 #endif
 121   sa_alignment_longdouble = sa_alignof (long double),
 122   sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
 123 #if HAVE_LONG_LONG_INT
 124                       | (sa_alignment_longlong - 1)
 125 #endif
 126                       | (sa_alignment_longdouble - 1)
 127                      ) + 1,
 128 /* The increment that guarantees room for a magic word must be >= sizeof (int)
 129    and a multiple of sa_alignment_max.  */
 130   sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max
 131 };
 132
 133 #endif /* _MALLOCA_H */