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Annotation of embedaddon/libiconv/srclib/malloca.h, revision 1.1.1.1

1.1       misho       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 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, write to the Free Software Foundation,
                     17:    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
                     18: 
                     19: #ifndef _MALLOCA_H
                     20: #define _MALLOCA_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) ((void) (N), NULL)
                     50: #endif
                     51: 
                     52: /* malloca(N) is a safe variant of alloca(N).  It allocates N bytes of
                     53:    memory allocated on the stack, that must be freed using freea() before
                     54:    the function returns.  Upon failure, it returns NULL.  */
                     55: #if HAVE_ALLOCA
                     56: # define malloca(N) \
                     57:   ((N) < 4032 - sa_increment                                       \
                     58:    ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \
                     59:    : mmalloca (N))
                     60: #else
                     61: # define malloca(N) \
                     62:   mmalloca (N)
                     63: #endif
                     64: extern void * mmalloca (size_t n);
                     65: 
                     66: /* Free a block of memory allocated through malloca().  */
                     67: #if HAVE_ALLOCA
                     68: extern void freea (void *p);
                     69: #else
                     70: # define freea free
                     71: #endif
                     72: 
                     73: /* nmalloca(N,S) is an overflow-safe variant of malloca (N * S).
                     74:    It allocates an array of N objects, each with S bytes of memory,
                     75:    on the stack.  S must be positive and N must be nonnegative.
                     76:    The array must be freed using freea() before the function returns.  */
                     77: #if 1
                     78: /* Cf. the definition of xalloc_oversized.  */
                     79: # define nmalloca(n, s) \
                     80:     ((n) > (size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) \
                     81:      ? NULL \
                     82:      : malloca ((n) * (s)))
                     83: #else
                     84: extern void * nmalloca (size_t n, size_t s);
                     85: #endif
                     86: 
                     87: 
                     88: #ifdef __cplusplus
                     89: }
                     90: #endif
                     91: 
                     92: 
                     93: /* ------------------- Auxiliary, non-public definitions ------------------- */
                     94: 
                     95: /* Determine the alignment of a type at compile time.  */
                     96: #if defined __GNUC__
                     97: # define sa_alignof __alignof__
                     98: #elif defined __cplusplus
                     99:   template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
                    100: # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
                    101: #elif defined __hpux
                    102:   /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
                    103:      values.  */
                    104: # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
                    105: #elif defined _AIX
                    106:   /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof
                    107:      values.  */
                    108: # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
                    109: #else
                    110: # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
                    111: #endif
                    112: 
                    113: enum
                    114: {
                    115: /* The desired alignment of memory allocations is the maximum alignment
                    116:    among all elementary types.  */
                    117:   sa_alignment_long = sa_alignof (long),
                    118:   sa_alignment_double = sa_alignof (double),
                    119: #if HAVE_LONG_LONG_INT
                    120:   sa_alignment_longlong = sa_alignof (long long),
                    121: #endif
                    122:   sa_alignment_longdouble = sa_alignof (long double),
                    123:   sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
                    124: #if HAVE_LONG_LONG_INT
                    125:                      | (sa_alignment_longlong - 1)
                    126: #endif
                    127:                      | (sa_alignment_longdouble - 1)
                    128:                     ) + 1,
                    129: /* The increment that guarantees room for a magic word must be >= sizeof (int)
                    130:    and a multiple of sa_alignment_max.  */
                    131:   sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max
                    132: };
                    133: 
                    134: #endif /* _MALLOCA_H */