bitmap: find_last_bit()

Impact: New API

As the name suggests.  For the moment everyone uses the generic one.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 45 insertions, 0 deletions

diff --git a/lib/find_last_bit.c b/lib/find_last_bit.c
new file mode 100644
index 000000000000..5d202e36bdd8
--- /dev/null
+++ b/lib/find_last_bit.c
@@ -0,0 +1,45 @@
+/* find_last_bit.c: fallback find next bit implementation
+ *
+ * Copyright (C) 2008 IBM Corporation
+ * Written by Rusty Russell <rusty@rustcorp.com.au>
+ * (Inspired by David Howell's find_next_bit implementation)
+ *
+ * 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.
+ */
+
+#include <linux/bitops.h>
+#include <linux/module.h>
+#include <asm/types.h>
+#include <asm/byteorder.h>
+
+unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
+{
+        unsigned long words;
+        unsigned long tmp;
+
+        /* Start at final word. */
+        words = size / BITS_PER_LONG;
+
+        /* Partial final word? */
+        if (size & (BITS_PER_LONG-1)) {
+                tmp = (addr[words] & (~0UL >> (BITS_PER_LONG
+                                         - (size & (BITS_PER_LONG-1)))));
+                if (tmp)
+                        goto found;
+        }
+
+        while (words) {
+                tmp = addr[--words];
+                if (tmp) {
+found:
+                        return words * BITS_PER_LONG + __fls(tmp);
+                }
+        }
+
+        /* Not found */
+        return size;
+}
+EXPORT_SYMBOL(find_last_bit);