bitmap: find_last_bit()
Rusty Russell [Wed, 31 Dec 2008 23:42:19 +0000 (09:42 +1030)]
Impact: New API

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

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

include/linux/bitops.h
lib/Kconfig
lib/Makefile
lib/find_last_bit.c [new file with mode: 0644]

index 024f2b0..6182913 100644 (file)
@@ -134,9 +134,20 @@ extern unsigned long find_first_bit(const unsigned long *addr,
  */
 extern unsigned long find_first_zero_bit(const unsigned long *addr,
                                         unsigned long size);
-
 #endif /* CONFIG_GENERIC_FIND_FIRST_BIT */
 
+#ifdef CONFIG_GENERIC_FIND_LAST_BIT
+/**
+ * find_last_bit - find the last set bit in a memory region
+ * @addr: The address to start the search at
+ * @size: The maximum size to search
+ *
+ * Returns the bit number of the first set bit, or size.
+ */
+extern unsigned long find_last_bit(const unsigned long *addr,
+                                  unsigned long size);
+#endif /* CONFIG_GENERIC_FIND_LAST_BIT */
+
 #ifdef CONFIG_GENERIC_FIND_NEXT_BIT
 
 /**
index 2ba43c4..fc5f5ee 100644 (file)
@@ -13,6 +13,10 @@ config GENERIC_FIND_FIRST_BIT
 config GENERIC_FIND_NEXT_BIT
        bool
 
+config GENERIC_FIND_LAST_BIT
+       bool
+       default y
+
 config CRC_CCITT
        tristate "CRC-CCITT functions"
        help
index 80fe8a3..32b0e64 100644 (file)
@@ -37,6 +37,7 @@ lib-$(CONFIG_RWSEM_GENERIC_SPINLOCK) += rwsem-spinlock.o
 lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
 lib-$(CONFIG_GENERIC_FIND_FIRST_BIT) += find_next_bit.o
 lib-$(CONFIG_GENERIC_FIND_NEXT_BIT) += find_next_bit.o
+lib-$(CONFIG_GENERIC_FIND_LAST_BIT) += find_last_bit.o
 obj-$(CONFIG_GENERIC_HWEIGHT) += hweight.o
 obj-$(CONFIG_LOCK_KERNEL) += kernel_lock.o
 obj-$(CONFIG_PLIST) += plist.o
diff --git a/lib/find_last_bit.c b/lib/find_last_bit.c
new file mode 100644 (file)
index 0000000..5d202e3
--- /dev/null
@@ -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);