From 62f75b2956e49a7c3aa58ac642f9acad193a2ac0 Mon Sep 17 00:00:00 2001
From: Andrew Morton <akpm@osdl.org>
Date: Sat, 4 Oct 2003 21:03:09 -0700
Subject: [PATCH] [PATCH] document the macro for translating PROT_ to VM_ bits

From: Muli Ben-Yehuda <mulix@mulix.org>

Shed some much-needed light.
---
 include/linux/mman.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/mman.h b/include/linux/mman.h
index cfb6ac61bbdef..07da84fcbd153 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -28,8 +28,13 @@ static inline void vm_unacct_memory(long pages)
 	vm_acct_memory(-pages);
 }
 
-/* Optimisation macro. */
-#define _calc_vm_trans(x,bit1,bit2) \
+/*
+ * Optimisation macro.  It is equivalent to:
+ *      (x & bit1) ? bit2 : 0
+ * but this version is faster.
+ * ("bit1" and "bit2" must be single bits)
+ */
+#define _calc_vm_trans(x, bit1, bit2) \
   ((bit1) <= (bit2) ? ((x) & (bit1)) * ((bit2) / (bit1)) \
    : ((x) & (bit1)) / ((bit1) / (bit2)))
 
-- 
2.53.0