new macro 'ispow2'

1 files changed, 7 insertions, 1 deletions

diff --git a/llimits.h b/llimits.h
index 725d7c8b..715d55b8 100644
--- a/llimits.h
+++ b/llimits.h
@@ -1,5 +1,5 @@
 /*
-** $Id: llimits.h,v 1.149 2018/01/28 15:13:26 roberto Exp roberto $
+** $Id: llimits.h,v 1.150 2018/05/30 14:25:52 roberto Exp roberto $
 ** Limits, basic types, and some other 'installation-dependent' definitions
 ** See Copyright Notice in lua.h
 */
@@ -60,6 +60,12 @@ typedef signed char ls_byte;
 
 
 /*
+** test whether an unsigned value is a power of 2 (or zero)
+*/
+#define ispow2(x)       (((x) & ((x) - 1)) == 0)
+
+
+/*
 ** conversion of pointer to unsigned integer:
 ** this is for hashing only; there is no problem if the integer
 ** cannot hold the whole pointer value