From 07da7b2d454833089c2c9fd8a657a2698de3c73a Mon Sep 17 00:00:00 2001
From: Oleg Hahm <oleg@hobbykeller.org>
Date: Mon, 9 Dec 2013 22:44:53 +0100
Subject: [PATCH] reverted 18e97f6dd5457538c7bf39c6abcf346f5a080ca5

---
 core/bitarithm.c         | 27 ++++++++++++++++++++++++++-
 core/include/bitarithm.h | 14 +++++++++-----
 2 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/core/bitarithm.c b/core/bitarithm.c
index 40eefd7bb1..cda4b6e280 100644
--- a/core/bitarithm.c
+++ b/core/bitarithm.c
@@ -11,7 +11,6 @@
  * \{
  * \file
  * \author Kaspar Schleiser <kaspar@schleiser.de>
- * \author Martin Lenders <mlenders@inf.fu-berlin.de>
  * \}
  */
 
@@ -40,3 +39,29 @@ 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 1df68464c1..6f38b28397 100644
--- a/core/include/bitarithm.h
+++ b/core/include/bitarithm.h
@@ -13,7 +13,6 @@
  * @file
  * @author Freie Universität Berlin, Computer Systems & Telematics
  * @author Kaspar Schleiser <kaspar@schleiser.de>
- * @author Martin Lenders <mlenders@inf.fu-berlin.de>
  */
 
 #ifndef BITARITHM_H_
@@ -79,17 +78,22 @@ unsigned number_of_highest_bit(unsigned v);
 
 /**
  * @brief	Returns the number of the lowest '1' bit in a value
- * @param[in]	v	Input value
- * @return			Bit Number, 0 for least significant bit, -1 if input is 0
+ * @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
  */
-#define number_of_lowest_bit(v) (__builtin_ffs(v)-1)
+unsigned number_of_lowest_bit(register unsigned v);
 
 /**
  * @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
  */
-#define number_of_bits_set(v) (__builtin_popcount(v))
+unsigned number_of_bits_set(unsigned v);
 
 /**
  * @}