[patch 12/47] generic find_{next,first}{,_zero}_bit()

Akinobu Mita
2006-02-14T05:04:03Z

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>
include/asm-generic/bitops/find.h | 13 ++++
lib/find_next_bit.c | 114 +++++++++++++++++++++++++++-----------
2 files changed, 95 insertions(+), 32 deletions(-)

Index: 2.6-rc/include/asm-generic/bitops/find.h
=================================--- /dev/null
+++ 2.6-rc/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_ */
Index: 2.6-rc/lib/find_next_bit.c
=================================--- 2.6-rc.orig/lib/find_next_bit.c
+++ 2.6-rc/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;
+
+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);
+}

- while ((tmp = *addr) = 0)
- addr++;
+EXPORT_SYMBOL(find_next_bit);

- offset = (addr - base) * NBITS;
+/*
+ * 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;

- finish:
- /* count the remaining bits without using __ffs() since that takes a 32-bit arg */
- while (!(tmp & 0xff)) {
- offset += 8;
- tmp >>= 8;
+ 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 (!(tmp & 1)) {
- offset++;
- tmp >>= 1;
+ while (size & ~(BITS_PER_LONG-1)) {
+ if (~(tmp = *(p++)))
+ goto found_middle;
+ result += BITS_PER_LONG;
+ size -= BITS_PER_LONG;
}
-
- return offset;
+ 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);
}

-EXPORT_SYMBOL(find_next_bit);
+EXPORT_SYMBOL(find_next_zero_bit);

--