1 files changed, 13 insertions, 0 deletions
diff --git a/perl.h b/perl.h
index 2deb1d4f0c..2d3e1f769d 100644
--- a/perl.h
+++ b/perl.h
@@ -1754,6 +1754,19 @@ typedef UVTYPE UV;
 #define PTR2NV(p)	NUM2PTR(NV,p)
 #define PTR2nat(p)	(PTRV)(p)	/* pointer to integer of PTRSIZE */
 
+
+#if PTRSIZE == 8
+#  define PTRSIZELOG2 3
+#elif PTRSIZE == 4
+#  define PTRSIZELOG2 2
+#  else
+#    error unknown pointer size
+#  endif
+
+/* idx = PTRPTR2IDX(offset)
+        -turn an offset into array of void *s into an index into the array */
+#define PTRPTR2IDX(offset) ((offset) >> PTRSIZELOG2)
+
 /* According to strict ANSI C89 one cannot freely cast between
  * data pointers and function (code) pointers.  There are at least
  * two ways around this.  One (used below) is to do two casts,