2006-02-01 09:19:59

by Akinobu Mita

Subject: [patch 11/44] 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 <[email protected]>
include/asm-generic/bitops/find.h | 99 ++++++++++++++++++++++++++++++++++++++
1 files changed, 99 insertions(+)

Index: 2.6-git/include/asm-generic/bitops/find.h
===================================================================
--- /dev/null
+++ 2.6-git/include/asm-generic/bitops/find.h
@@ -0,0 +1,99 @@
+#ifndef _ASM_GENERIC_BITOPS_FIND_H_
+#define _ASM_GENERIC_BITOPS_FIND_H_
+
+#include <asm/types.h>
+
+#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
+ */
+static inline unsigned long find_next_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;
+
+ if (offset >= size)
+ return size;
+ size -= result;
+ offset %= BITS_PER_LONG;
+ if (offset) {
+ 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;
+
+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);
+}
+
+/*
+ * This implementation of find_{first,next}_zero_bit was stolen from
+ * Linus' asm-alpha/bitops.h.
+ */
+static inline 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;
+
+ 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;
+
+found_first:
+ tmp |= ~0UL << size;
+ if (tmp == ~0UL) /* Are any bits zero? */
+ return result + size; /* Nope. */
+found_middle:
+ return result + ffz(tmp);
+}
+
+#define find_first_zero_bit(addr, size) find_next_zero_bit((addr), (size), 0)
+#define find_first_bit(addr, size) find_next_bit((addr), (size), 0)
+
+#endif /*_ASM_GENERIC_BITOPS_FIND_H_ */

--

2006-02-06 10:27:09

by David Howells

Subject: Re: [patch 11/44] generic find_{next,first}{,_zero}_bit()

Akinobu Mita <[email protected]> wrote:

> 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);

These big functions should perhaps be out of line.

David

2006-02-07 02:02:26

by Akinobu Mita

Subject: Re: [patch 11/44] generic find_{next,first}{,_zero}_bit()

On Mon, Feb 06, 2006 at 10:26:00AM +0000, David Howells wrote:
> Akinobu Mita <[email protected]> wrote:
>
> > 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);
>
> These big functions should perhaps be out of line.

Yes. I'll make them and below out of line.

- hweight*()
- ext2_find_*_zero_bit()
- minix_find_first_zero_bit()