[PATCH] bitops: generic find_{next,first}{,_zero}_bit()

This patch introduces the C-language equivalents of the functions below:

unsigned logn find_next_bit(const unsigned long *addr, unsigned long size,
                            unsigned long offset);
unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
                                 unsigned long offset);
unsigned long find_first_zero_bit(const unsigned long *addr,
                                  unsigned long size);
unsigned long find_first_bit(const unsigned long *addr, unsigned long size);

In include/asm-generic/bitops/find.h

This code largely copied from: arch/powerpc/lib/bitops.c

Signed-off-by: Akinobu Mita <mita@miraclelinux.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/include/asm-generic/bitops/find.h b/include/asm-generic/bitops/find.h
new file mode 100644 (file)
index 0000000..72a51e5
--- /dev/null
+++ b/include/asm-generic/bitops/find.h
@@ -0,0 +1,13 @@
+#ifndef _ASM_GENERIC_BITOPS_FIND_H_
+#define _ASM_GENERIC_BITOPS_FIND_H_
+
+extern unsigned long find_next_bit(const unsigned long *addr, unsigned long
+               size, unsigned long offset);
+
+extern unsigned long find_next_zero_bit(const unsigned long *addr, unsigned
+               long size, unsigned long offset);
+
+#define find_first_bit(addr, size) find_next_bit((addr), (size), 0)
+#define find_first_zero_bit(addr, size) find_next_zero_bit((addr), (size), 0)
+
+#endif /*_ASM_GENERIC_BITOPS_FIND_H_ */

diff --git a/lib/find_next_bit.c b/lib/find_next_bit.c
index c05b4b19cf6cac90e407eac98e870130bbb3e66a..9c90853b4472b85eb9b7d17e56ae69182f718467 100644 (file)
--- a/lib/find_next_bit.c
+++ b/lib/find_next_bit.c
@@ -11,48 +11,98 @@
 
 #include <linux/bitops.h>
 #include <linux/module.h>
+#include <asm/types.h>
 
-int find_next_bit(const unsigned long *addr, int size, int offset)
+#define BITOP_WORD(nr)         ((nr) / BITS_PER_LONG)
+
+/**
+ * find_next_bit - find the next set bit in a memory region
+ * @addr: The address to base the search on
+ * @offset: The bitnumber to start searching at
+ * @size: The maximum size to search
+ */
+unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
+               unsigned long offset)
 {
-       const unsigned long *base;
-       const int NBITS = sizeof(*addr) * 8;
+       const unsigned long *p = addr + BITOP_WORD(offset);
+       unsigned long result = offset & ~(BITS_PER_LONG-1);
        unsigned long tmp;
 
-       base = addr;
+       if (offset >= size)
+               return size;
+       size -= result;
+       offset %= BITS_PER_LONG;
        if (offset) {
-               int suboffset;
-
-               addr += offset / NBITS;
-
-               suboffset = offset % NBITS;
-               if (suboffset) {
-                       tmp = *addr;
-                       tmp >>= suboffset;
-                       if (tmp)
-                               goto finish;
-               }
-
-               addr++;
+               tmp = *(p++);
+               tmp &= (~0UL << offset);
+               if (size < BITS_PER_LONG)
+                       goto found_first;
+               if (tmp)
+                       goto found_middle;
+               size -= BITS_PER_LONG;
+               result += BITS_PER_LONG;
+       }
+       while (size & ~(BITS_PER_LONG-1)) {
+               if ((tmp = *(p++)))
+                       goto found_middle;
+               result += BITS_PER_LONG;
+               size -= BITS_PER_LONG;
        }
+       if (!size)
+               return result;
+       tmp = *p;
 
-       while ((tmp = *addr) == 0)
-               addr++;
+found_first:
+       tmp &= (~0UL >> (BITS_PER_LONG - size));
+       if (tmp == 0UL)         /* Are any bits set? */
+               return result + size;   /* Nope. */
+found_middle:
+       return result + __ffs(tmp);
+}
 
-       offset = (addr - base) * NBITS;
+EXPORT_SYMBOL(find_next_bit);
 
- finish:
-       /* count the remaining bits without using __ffs() since that takes a 32-bit arg */
-       while (!(tmp & 0xff)) {
-               offset += 8;
-               tmp >>= 8;
-       }
+/*
+ * This implementation of find_{first,next}_zero_bit was stolen from
+ * Linus' asm-alpha/bitops.h.
+ */
+unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
+               unsigned long offset)
+{
+       const unsigned long *p = addr + BITOP_WORD(offset);
+       unsigned long result = offset & ~(BITS_PER_LONG-1);
+       unsigned long tmp;
 
-       while (!(tmp & 1)) {
-               offset++;
-               tmp >>= 1;
+       if (offset >= size)
+               return size;
+       size -= result;
+       offset %= BITS_PER_LONG;
+       if (offset) {
+               tmp = *(p++);
+               tmp |= ~0UL >> (BITS_PER_LONG - offset);
+               if (size < BITS_PER_LONG)
+                       goto found_first;
+               if (~tmp)
+                       goto found_middle;
+               size -= BITS_PER_LONG;
+               result += BITS_PER_LONG;
+       }
+       while (size & ~(BITS_PER_LONG-1)) {
+               if (~(tmp = *(p++)))
+                       goto found_middle;
+               result += BITS_PER_LONG;
+               size -= BITS_PER_LONG;
        }
+       if (!size)
+               return result;
+       tmp = *p;
 
-       return offset;
+found_first:
+       tmp |= ~0UL << size;
+       if (tmp == ~0UL)        /* Are any bits zero? */
+               return result + size;   /* Nope. */
+found_middle:
+       return result + ffz(tmp);
 }
 
-EXPORT_SYMBOL(find_next_bit);
+EXPORT_SYMBOL(find_next_zero_bit);