handy.h: Create nBIT_MASK(n) macro

This encapsulates a common paradigm, making sure that it is done
correctly for the platform's size.

1 files changed, 7 insertions, 0 deletions

diff --git a/handy.h b/handy.h
index 4451e9d46d..7f0741732e 100644
--- a/handy.h
+++ b/handy.h
@@ -269,6 +269,13 @@ typedef U64TYPE U64;
 #  define isPOWER_OF_2(n) ((n) && ((n) & ((n)-1)) == 0)
 #endif
 
+/* Returns a mask with the lowest n bits set */
+#ifdef HAS_LONG_LONG
+#  define nBIT_MASK(n) ((1ULL << (n)) - 1)
+#else
+#  define nBIT_MASK(n) ((1UL << (n)) - 1)
+#endif
+
 /*
 =for apidoc Am|void|__ASSERT_|bool expr