From 18e97f6dd5457538c7bf39c6abcf346f5a080ca5 Mon Sep 17 00:00:00 2001
From: authmillenon <mlenders@inf.fu-berlin.de>
Date: Sun, 3 Nov 2013 14:32:25 +0100
Subject: [PATCH] Use GCC/Clang builtins for bit arithmetics

---
 core/bitarithm.c         | 27 +--------------------------
 core/include/bitarithm.h | 14 +++++---------
 sys/include/posix_io.h   | 24 +++++++++++++++++++++++-
 3 files changed, 29 insertions(+), 36 deletions(-)

diff --git a/core/bitarithm.c b/core/bitarithm.c
index dec36185d3..e43d97b808 100644
--- a/core/bitarithm.c
+++ b/core/bitarithm.c
@@ -11,6 +11,7 @@
  * \{
  * \file
  * \author Kaspar Schleiser <kaspar.schleiser@fu-berlin.de>
+ * \author Martin Lenders <mlenders@inf.fu-berlin.de>
  * \}
  */
 
@@ -39,29 +40,3 @@ number_of_highest_bit(unsigned v)
 
     return r;
 }
-/*---------------------------------------------------------------------------*/
-unsigned
-number_of_lowest_bit(register unsigned v)
-{
-    register unsigned r = 0;
-
-    while ((v & 0x01) == 0) {
-        v >>= 1;
-        r++;
-    };
-
-    return r;
-}
-/*---------------------------------------------------------------------------*/
-unsigned
-number_of_bits_set(unsigned v)
-{
-    unsigned c; // c accumulates the total bits set in v
-
-    for (c = 0; v; c++) {
-        v &= v - 1; // clear the least significant bit set
-    }
-
-    return c;
-}
-
diff --git a/core/include/bitarithm.h b/core/include/bitarithm.h
index 83eacb1d68..1bca83acb1 100644
--- a/core/include/bitarithm.h
+++ b/core/include/bitarithm.h
@@ -13,6 +13,7 @@
  * @file
  * @author Freie Universität Berlin, Computer Systems & Telematics
  * @author Kaspar Schleiser <kaspar.schleiser@fu-berlin.de>
+ * @author Martin Lenders <mlenders@inf.fu-berlin.de>
  */
 
 #ifndef BITARITHM_H_
@@ -78,22 +79,17 @@ unsigned number_of_highest_bit(unsigned v);
 
 /**
  * @brief	Returns the number of the lowest '1' bit in a value
- * @param[in]	v	Input value - must be unequal to '0', otherwise the
- *                  function will produce an infinite loop
- * @return			Bit Number
- *
- * Source: http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogObvious
+ * @param[in]	v	Input value
+ * @return			Bit Number, 0 for least significant bit, -1 if input is 0
  */
-unsigned number_of_lowest_bit(register unsigned v);
+#define number_of_lowest_bit(v) (__builtin_ffs(v)-1)
 
 /**
  * @brief	Returns the number of bits set in a value
  * @param[in]	v	Input value
  * @return			Number of set bits
- *
- * Source: http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogObvious
  */
-unsigned number_of_bits_set(unsigned v);
+#define number_of_bits_set(v) (__builtin_popcount(v))
 
 /**
  * @}
diff --git a/sys/include/posix_io.h b/sys/include/posix_io.h
index bb9ad426a4..b4fe27378e 100644
--- a/sys/include/posix_io.h
+++ b/sys/include/posix_io.h
@@ -1,3 +1,23 @@
+/**
+ * Copyright (C) 2013  INRIA.
+ *
+ * This file subject to the terms and conditions of the GNU Lesser General
+ * Public License. See the file LICENSE in the top level directory for more
+ * details.
+ */
+
+/** 
+ * @addtogroup posix
+ * @{
+ * @file
+ * @brief   POSIX-like IO
+ *
+ * @author Freie Universität Berlin
+ * @author Kaspar Schleiser <kaspar@schleiser.de>
+ * @author Stephan Zeisberg <zeisberg@mi.fu-berlin.de>
+ * @author Oliver Hahm <oleg@hobbykeller.org>
+ * @author Martin Lenders <mlenders@inf.fu-berlin.de>
+ */
 #ifndef __READ_H
 #define __READ_H
 
@@ -15,5 +35,7 @@ int posix_open(int pid, int flags);
 int posix_close(int pid);
 int posix_read(int pid, char *buffer, int bufsize);
 int posix_write(int pid, char *buffer, int bufsize);
-
+/**
+ * @}
+ */
 #endif /* __READ_H */