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authorAndreas Rottmann <a.rottmann@gmx.at>2009-09-14 12:32:44 +0200
committerAndreas Rottmann <a.rottmann@gmx.at>2009-09-14 12:32:44 +0200
commitfa095a4504cbe668e4244547e2c141597bea4ecf (patch)
tree06135820a286ffec47804e75fbf8a147e92acd2e /lib/malloca.c
Imported Upstream version 0.9.1upstream/0.9.1
Diffstat (limited to 'lib/malloca.c')
-rw-r--r--lib/malloca.c137
1 files changed, 137 insertions, 0 deletions
diff --git a/lib/malloca.c b/lib/malloca.c
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+/* Safe automatic memory allocation.
+ Copyright (C) 2003, 2006-2007 Free Software Foundation, Inc.
+ Written by Bruno Haible <bruno@clisp.org>, 2003.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU Lesser General Public License as published by
+ the Free Software Foundation; either version 2, or (at your option)
+ any later version.
+
+ This program 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 Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License
+ along with this program; if not, write to the Free Software Foundation,
+ Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
+
+#include <config.h>
+
+/* Specification. */
+#include "malloca.h"
+
+/* The speed critical point in this file is freea() applied to an alloca()
+ result: it must be fast, to match the speed of alloca(). The speed of
+ mmalloca() and freea() in the other case are not critical, because they
+ are only invoked for big memory sizes. */
+
+#if HAVE_ALLOCA
+
+/* Store the mmalloca() results in a hash table. This is needed to reliably
+ distinguish a mmalloca() result and an alloca() result.
+
+ Although it is possible that the same pointer is returned by alloca() and
+ by mmalloca() at different times in the same application, it does not lead
+ to a bug in freea(), because:
+ - Before a pointer returned by alloca() can point into malloc()ed memory,
+ the function must return, and once this has happened the programmer must
+ not call freea() on it anyway.
+ - Before a pointer returned by mmalloca() can point into the stack, it
+ must be freed. The only function that can free it is freea(), and
+ when freea() frees it, it also removes it from the hash table. */
+
+#define MAGIC_NUMBER 0x1415fb4a
+#define MAGIC_SIZE sizeof (int)
+/* This is how the header info would look like without any alignment
+ considerations. */
+struct preliminary_header { void *next; char room[MAGIC_SIZE]; };
+/* But the header's size must be a multiple of sa_alignment_max. */
+#define HEADER_SIZE \
+ (((sizeof (struct preliminary_header) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max)
+struct header { void *next; char room[HEADER_SIZE - sizeof (struct preliminary_header) + MAGIC_SIZE]; };
+/* Verify that HEADER_SIZE == sizeof (struct header). */
+typedef int verify1[2 * (HEADER_SIZE == sizeof (struct header)) - 1];
+/* We make the hash table quite big, so that during lookups the probability
+ of empty hash buckets is quite high. There is no need to make the hash
+ table resizable, because when the hash table gets filled so much that the
+ lookup becomes slow, it means that the application has memory leaks. */
+#define HASH_TABLE_SIZE 257
+static void * mmalloca_results[HASH_TABLE_SIZE];
+
+#endif
+
+void *
+mmalloca (size_t n)
+{
+#if HAVE_ALLOCA
+ /* Allocate one more word, that serves as an indicator for malloc()ed
+ memory, so that freea() of an alloca() result is fast. */
+ size_t nplus = n + HEADER_SIZE;
+
+ if (nplus >= n)
+ {
+ char *p = (char *) malloc (nplus);
+
+ if (p != NULL)
+ {
+ size_t slot;
+
+ p += HEADER_SIZE;
+
+ /* Put a magic number into the indicator word. */
+ ((int *) p)[-1] = MAGIC_NUMBER;
+
+ /* Enter p into the hash table. */
+ slot = (unsigned long) p % HASH_TABLE_SIZE;
+ ((struct header *) (p - HEADER_SIZE))->next = mmalloca_results[slot];
+ mmalloca_results[slot] = p;
+
+ return p;
+ }
+ }
+ /* Out of memory. */
+ return NULL;
+#else
+# if !MALLOC_0_IS_NONNULL
+ if (n == 0)
+ n = 1;
+# endif
+ return malloc (n);
+#endif
+}
+
+#if HAVE_ALLOCA
+void
+freea (void *p)
+{
+ /* mmalloca() may have returned NULL. */
+ if (p != NULL)
+ {
+ /* Attempt to quickly distinguish the mmalloca() result - which has
+ a magic indicator word - and the alloca() result - which has an
+ uninitialized indicator word. It is for this test that sa_increment
+ additional bytes are allocated in the alloca() case. */
+ if (((int *) p)[-1] == MAGIC_NUMBER)
+ {
+ /* Looks like a mmalloca() result. To see whether it really is one,
+ perform a lookup in the hash table. */
+ size_t slot = (unsigned long) p % HASH_TABLE_SIZE;
+ void **chain = &mmalloca_results[slot];
+ for (; *chain != NULL;)
+ {
+ if (*chain == p)
+ {
+ /* Found it. Remove it from the hash table and free it. */
+ char *p_begin = (char *) p - HEADER_SIZE;
+ *chain = ((struct header *) p_begin)->next;
+ free (p_begin);
+ return;
+ }
+ chain = &((struct header *) ((char *) *chain - HEADER_SIZE))->next;
+ }
+ }
+ /* At this point, we know it was not a mmalloca() result. */
+ }
+}
+#endif