[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>

2 files changed, 94 insertions, 31 deletions

diff --git a/include/asm-generic/bitops/find.h b/include/asm-generic/bitops/find.h
new file mode 100644
index 000000000000..72a51e5a12ef
--- /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 c05b4b19cf6c..9c90853b4472 100644
--- 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);