add ffs functions

Signed-off-by: Mattias Andrée <maandree@operamail.com>

2 files changed, 83 insertions, 0 deletions

diff --git a/include/strings.h b/include/strings.h
index 224c9a4..7a02d1e 100644
--- a/include/strings.h
+++ b/include/strings.h
@@ -145,6 +145,34 @@ char* rindex(const char*, int)
   __GCC_ONLY(__attribute__((warn_unused_result, nonnull, pure)));
 
 
+/**
+ * Find the first set bit in an integer.
+ * 
+ * @param   i  The integer
+ * @return     The value of the least significant set bit, zero if none.
+ */
+int ffs(int)
+  __GCC_ONLY(__attribute__((warn_unused_result, const)));
+
+/**
+ * Find the first set bit in an integer.
+ * 
+ * @param   i  The integer
+ * @return     The value of the least significant set bit, zero if none.
+ */
+int ffsl(long)
+  __GCC_ONLY(__attribute__((warn_unused_result, const)));
+
+/**
+ * Find the first set bit in an integer.
+ * 
+ * @param   i  The integer
+ * @return     The value of the least significant set bit, zero if none.
+ */
+int ffsll(long long)
+  __GCC_ONLY(__attribute__((warn_unused_result, const)));
+
+
 
 #endif
 
diff --git a/src/strings/ffs.c b/src/strings/ffs.c
new file mode 100644
index 0000000..b0a6481
--- /dev/null
+++ b/src/strings/ffs.c
@@ -0,0 +1,55 @@
+/**
+ * slibc — Yet another C library
+ * Copyright © 2015  Mattias Andrée (maandree@member.fsf.org)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <strings.h>
+
+
+/**
+ * Find the first set bit in an integer.
+ * 
+ * @param   i  The integer
+ * @return     The value of the least significant set bit, zero if none.
+ */
+int ffs(int i)
+{
+  return __builtin_ffs(i);
+}
+
+
+/**
+ * Find the first set bit in an integer.
+ * 
+ * @param   i  The integer
+ * @return     The value of the least significant set bit, zero if none.
+ */
+int ffsl(long i)
+{
+  return __builtin_ffsl(i);
+}
+
+
+/**
+ * Find the first set bit in an integer.
+ * 
+ * @param   i  The integer
+ * @return     The value of the least significant set bit, zero if none.
+ */
+int ffsll(long long i)
+{
+  return __builtin_ffsll(i);
+}
+