1 files changed, 112 insertions, 0 deletions
diff --git a/lib/malloca.c b/lib/malloca.c
new file mode 100644
index 0000000..f055b1e
--- /dev/null
+++ b/lib/malloca.c
@@ -0,0 +1,112 @@
+/* Safe automatic memory allocation.
+   Copyright (C) 2003, 2006-2007, 2009-2023 Free Software Foundation, Inc.
+   Written by Bruno Haible <bruno@clisp.org>, 2003, 2018.
+
+   This file 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 2.1 of the
+   License, or (at your option) any later version.
+
+   This file 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, see <https://www.gnu.org/licenses/>.  */
+
+#define _GL_USE_STDLIB_ALLOC 1
+#include <config.h>
+
+/* Specification.  */
+#include "malloca.h"
+
+#include <stdckdint.h>
+
+#include "idx.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.
+   Here we use a bit in the address as an indicator, an idea by Ondřej Bílka.
+   malloca() can return three types of pointers:
+     - Pointers ≡ 0 mod 2*sa_alignment_max come from stack allocation.
+     - Pointers ≡ sa_alignment_max mod 2*sa_alignment_max come from heap
+       allocation.
+     - NULL comes from a failed heap allocation.  */
+
+/* Type for holding very small pointer differences.  */
+typedef unsigned char small_t;
+/* Verify that it is wide enough.  */
+static_assert (2 * sa_alignment_max - 1 <= (small_t) -1);
+
+void *
+mmalloca (size_t n)
+{
+#if HAVE_ALLOCA
+  /* Allocate one more word, used to determine the address to pass to freea(),
+     and room for the alignment ≡ sa_alignment_max mod 2*sa_alignment_max.  */
+  uintptr_t alignment2_mask = 2 * sa_alignment_max - 1;
+  int plus = sizeof (small_t) + alignment2_mask;
+  idx_t nplus;
+  if (!ckd_add (&nplus, n, plus) && !xalloc_oversized (nplus, 1))
+    {
+      char *mem = (char *) malloc (nplus);
+
+      if (mem != NULL)
+        {
+          uintptr_t umem = (uintptr_t)mem, umemplus;
+          /* The ckd_add avoids signed integer overflow on
+             theoretical platforms where UINTPTR_MAX <= INT_MAX.  */
+          ckd_add (&umemplus, umem, sizeof (small_t) + sa_alignment_max - 1);
+          idx_t offset = ((umemplus & ~alignment2_mask)
+                          + sa_alignment_max - umem);
+          void *vp = mem + offset;
+          small_t *p = vp;
+          /* Here p >= mem + sizeof (small_t),
+             and p <= mem + sizeof (small_t) + 2 * sa_alignment_max - 1
+             hence p + n <= mem + nplus.
+             So, the memory range [p, p+n) lies in the allocated memory range
+             [mem, mem + nplus).  */
+          p[-1] = offset;
+          /* p ≡ sa_alignment_max mod 2*sa_alignment_max.  */
+          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)
+{
+  /* Check argument.  */
+  if ((uintptr_t) p & (sa_alignment_max - 1))
+    {
+      /* p was not the result of a malloca() call.  Invalid argument.  */
+      abort ();
+    }
+  /* Determine whether p was a non-NULL pointer returned by mmalloca().  */
+  if ((uintptr_t) p & sa_alignment_max)
+    {
+      void *mem = (char *) p - ((small_t *) p)[-1];
+      free (mem);
+    }
+}
+#endif
+
+/*
+ * Hey Emacs!
+ * Local Variables:
+ * coding: utf-8
+ * End:
+ */