Import the log2 module from X15 and relicense to GPLv2+

* kern/log2.h: New file.

1 files changed, 50 insertions, 0 deletions

diff --git a/kern/log2.h b/kern/log2.h
new file mode 100644
index 00000000..0e67701c
--- /dev/null
+++ b/kern/log2.h
@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2014 Richard Braun.
+ *
+ * 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 2 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/>.
+ *
+ *
+ * Integer base 2 logarithm operations.
+ */
+
+#ifndef _KERN_LOG2_H
+#define _KERN_LOG2_H
+
+#include <kern/assert.h>
+
+#ifdef __LP64__
+#define LONG_BIT 64
+#else /* __LP64__ */
+#define LONG_BIT 32
+#endif /* __LP64__ */
+
+static inline unsigned int
+ilog2(unsigned long x)
+{
+    assert(x != 0);
+    return LONG_BIT - __builtin_clzl(x) - 1;
+}
+
+static inline unsigned int
+iorder2(unsigned long size)
+{
+    assert(size != 0);
+
+    if (size == 1)
+        return 0;
+
+    return ilog2(size - 1) + 1;
+}
+
+#endif /* _KERN_LOG2_H */