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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 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 General Public License for more details.
+
+   You should have received a copy of the GNU 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