+/* SAFE_ALLOCA normally allocates memory on the stack, but if size is
+ larger than MAX_ALLOCA, use xmalloc to avoid overflowing the stack. */
+
+#define MAX_ALLOCA 16*1024
+
+extern Lisp_Object safe_alloca_unwind (Lisp_Object);
+
+#define USE_SAFE_ALLOCA \
+ int sa_count = SPECPDL_INDEX (), sa_must_free = 0
+
+/* SAFE_ALLOCA allocates a simple buffer. */
+
+#define SAFE_ALLOCA(buf, type, size) \
+ do { \
+ if ((size) < MAX_ALLOCA) \
+ buf = (type) alloca (size); \
+ else \
+ { \
+ buf = (type) xmalloc (size); \
+ sa_must_free++; \
+ record_unwind_protect (safe_alloca_unwind, \
+ make_save_value (buf, 0)); \
+ } \
+ } while (0)
+
+/* SAFE_FREE frees xmalloced memory and enables GC as needed. */
+
+#define SAFE_FREE() \
+ do { \
+ if (sa_must_free) { \
+ sa_must_free = 0; \
+ unbind_to (sa_count, Qnil); \
+ } \
+ } while (0)
+
+
+/* SAFE_ALLOCA_LISP allocates an array of Lisp_Objects. */
+
+#define SAFE_ALLOCA_LISP(buf, nelt) \
+ do { \
+ int size_ = (nelt) * sizeof (Lisp_Object); \
+ if (size_ < MAX_ALLOCA) \
+ buf = (Lisp_Object *) alloca (size_); \
+ else \
+ { \
+ Lisp_Object arg_; \
+ buf = (Lisp_Object *) xmalloc (size_); \
+ arg_ = make_save_value (buf, nelt); \
+ XSAVE_VALUE (arg_)->dogc = 1; \
+ sa_must_free++; \
+ record_unwind_protect (safe_alloca_unwind, arg_); \
+ } \
+ } while (0)
+
+