1: /* Safe automatic memory allocation.
    2:    Copyright (C) 2003-2007 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 2, 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, write to the Free Software Foundation,
   17:    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
   18: 
   19: #ifndef _ALLOCSA_H
   20: #define _ALLOCSA_H
   21: 
   22: #include <alloca.h>
   23: #include <stddef.h>
   24: #include <stdlib.h>
   25: 
   26: 
   27: #ifdef __cplusplus
   28: extern "C" {
   29: #endif
   30: 
   31: 
   32: /* safe_alloca(N) is equivalent to alloca(N) when it is safe to call
   33:    alloca(N); otherwise it returns NULL.  It either returns N bytes of
   34:    memory allocated on the stack, that lasts until the function returns,
   35:    or NULL.
   36:    Use of safe_alloca should be avoided:
   37:      - inside arguments of function calls - undefined behaviour,
   38:      - in inline functions - the allocation may actually last until the
   39:        calling function returns.
   40: */
   41: #if HAVE_ALLOCA
   42: /* The OS usually guarantees only one guard page at the bottom of the stack,
   43:    and a page size can be as small as 4096 bytes.  So we cannot safely
   44:    allocate anything larger than 4096 bytes.  Also care for the possibility
   45:    of a few compiler-allocated temporary stack slots.
   46:    This must be a macro, not an inline function.  */
   47: # define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL)
   48: #else
   49: # define safe_alloca(N) ((N), NULL)
   50: #endif
   51: 
   52: /* allocsa(N) is a safe variant of alloca(N).  It allocates N bytes of
   53:    memory allocated on the stack, that must be freed using freesa() before
   54:    the function returns.  Upon failure, it returns NULL.  */
   55: #if HAVE_ALLOCA
   56: # define allocsa(N) \
   57:   ((N) < 4032 - sa_increment                                        \
   58:    ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \
   59:    : mallocsa (N))
   60: #else
   61: # define allocsa(N) \
   62:   mallocsa (N)
   63: #endif
   64: extern void * mallocsa (size_t n);
   65: 
   66: /* Free a block of memory allocated through allocsa().  */
   67: #if HAVE_ALLOCA
   68: extern void freesa (void *p);
   69: #else
   70: # define freesa free
   71: #endif
   72: 
   73: /* Maybe we should also define a variant
   74:     nallocsa (size_t n, size_t s) - behaves like allocsa (n * s)
   75:    If this would be useful in your application. please speak up.  */
   76: 
   77: 
   78: #ifdef __cplusplus
   79: }
   80: #endif
   81: 
   82: 
   83: /* ------------------- Auxiliary, non-public definitions ------------------- */
   84: 
   85: /* Determine the alignment of a type at compile time.  */
   86: #if defined __GNUC__
   87: # define sa_alignof __alignof__
   88: #elif defined __cplusplus
   89:   template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
   90: # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
   91: #elif defined __hpux
   92:   /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
   93:      values.  */
   94: # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
   95: #elif defined _AIX
   96:   /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof
   97:      values.  */
   98: # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
   99: #else
  100: # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
  101: #endif
  102: 
  103: enum
  104: {
  105: /* The desired alignment of memory allocations is the maximum alignment
  106:    among all elementary types.  */
  107:   sa_alignment_long = sa_alignof (long),
  108:   sa_alignment_double = sa_alignof (double),
  109: #if HAVE_LONG_LONG_INT
  110:   sa_alignment_longlong = sa_alignof (long long),
  111: #endif
  112: #if HAVE_LONG_DOUBLE
  113:   sa_alignment_longdouble = sa_alignof (long double),
  114: #endif
  115:   sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
  116: #if HAVE_LONG_LONG_INT
  117:                       | (sa_alignment_longlong - 1)
  118: #endif
  119: #if HAVE_LONG_DOUBLE
  120:                       | (sa_alignment_longdouble - 1)
  121: #endif
  122:                      ) + 1,
  123: /* The increment that guarantees room for a magic word must be >= sizeof (int)
  124:    and a multiple of sa_alignment_max.  */
  125:   sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max
  126: };
  127: 
  128: #endif /* _ALLOCSA_H */