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Subject[PATCH] x86: generic versions of find_first_(zero_)bit, convert i386
Generic versions of __find_first_bit and __find_first_zero_bit
are introduced as simplified versions of __find_next_bit and
__find_next_zero_bit. Their compilation and use are guarded by
a new config variable GENERIC_FIND_FIRST_BIT.

The generic versions of find_first_bit and find_first_zero_bit
are implemented in terms of the newly introduced __find_first_bit
and __find_first_zero_bit.

This patch also converts i386 to the generic functions. The text
size shrinks slightly due to uninlining of the find_*_bit functions.

text data bss dec hex filename
4764939 480324 622592 5867855 59894f vmlinux (i386 defconfig before)
4764645 480324 622592 5867561 598829 vmlinux (i386 defconfig after)

Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>

---

Hi Ingo,

Here is another step in the unification of the bitops for i386
and x86_64. This patch implements a minimal conversion to a
generic implementation of find_first_bit/find_first_zero_bit
for i386. The optimization for small bitmaps and the conversion
of x86_64 will follow soon.

Compiles and runs fine on i386 and x86_64 (current x86#testing).

Greetings,
Alexander

arch/x86/Kconfig | 3 ++
include/asm-x86/bitops_32.h | 56 -----------------------------------------
include/linux/bitops.h | 34 +++++++++++++++++++++++++
lib/Makefile | 1 +
lib/find_next_bit.c | 58 +++++++++++++++++++++++++++++++++++++++++++
5 files changed, 96 insertions(+), 56 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6b3626d..fa7d16d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -80,6 +80,9 @@ config GENERIC_BUG
def_bool y
depends on BUG

+config GENERIC_FIND_FIRST_BIT
+ def_bool X86_32
+
config GENERIC_FIND_NEXT_BIT
def_bool y

diff --git a/include/asm-x86/bitops_32.h b/include/asm-x86/bitops_32.h
index 3ed64b2..2e86302 100644
--- a/include/asm-x86/bitops_32.h
+++ b/include/asm-x86/bitops_32.h
@@ -4,62 +4,6 @@
/*
* Copyright 1992, Linus Torvalds.
*/
-
-/**
- * find_first_zero_bit - find the first zero 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 zero bit, not the number of the byte
- * containing a bit.
- */
-static inline int find_first_zero_bit(const unsigned long *addr, unsigned size)
-{
- int d0, d1, d2;
- int res;
-
- if (!size)
- return 0;
- /* This looks at memory.
- * Mark it volatile to tell gcc not to move it around
- */
- asm volatile("movl $-1,%%eax\n\t"
- "xorl %%edx,%%edx\n\t"
- "repe; scasl\n\t"
- "je 1f\n\t"
- "xorl -4(%%edi),%%eax\n\t"
- "subl $4,%%edi\n\t"
- "bsfl %%eax,%%edx\n"
- "1:\tsubl %%ebx,%%edi\n\t"
- "shll $3,%%edi\n\t"
- "addl %%edi,%%edx"
- : "=d" (res), "=&c" (d0), "=&D" (d1), "=&a" (d2)
- : "1" ((size + 31) >> 5), "2" (addr),
- "b" (addr) : "memory");
- return res;
-}
-
-/**
- * find_first_bit - find the first 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, not the number of the byte
- * containing a bit.
- */
-static inline unsigned find_first_bit(const unsigned long *addr, unsigned size)
-{
- unsigned x = 0;
-
- while (x < size) {
- unsigned long val = *addr++;
- if (val)
- return __ffs(val) + x;
- x += sizeof(*addr) << 3;
- }
- return x;
-}
-
#ifdef __KERNEL__

#include <asm-generic/bitops/sched.h>
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 3865f2c..355d67b 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -113,6 +113,40 @@ static inline unsigned fls_long(unsigned long l)
}

#ifdef __KERNEL__
+#ifdef CONFIG_GENERIC_FIND_FIRST_BIT
+extern unsigned long __find_first_bit(const unsigned long *addr,
+ unsigned long size);
+
+/**
+ * find_first_bit - find the first 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.
+ */
+static __always_inline unsigned long
+find_first_bit(const unsigned long *addr, unsigned long size)
+{
+ return __find_first_bit(addr, size);
+}
+
+extern unsigned long __find_first_zero_bit(const unsigned long *addr,
+ unsigned long size);
+
+/**
+ * find_first_zero_bit - find the first cleared 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 cleared bit.
+ */
+static __always_inline unsigned long
+find_first_zero_bit(const unsigned long *addr, unsigned long size)
+{
+ return __find_first_zero_bit(addr, size);
+}
+#endif /* CONFIG_GENERIC_FIND_FIRST_BIT */
+
#ifdef CONFIG_GENERIC_FIND_NEXT_BIT
extern unsigned long __find_next_bit(const unsigned long *addr,
unsigned long size, unsigned long offset);
diff --git a/lib/Makefile b/lib/Makefile
index 23de261..14c93e1 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -30,6 +30,7 @@ obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock_debug.o
lib-$(CONFIG_RWSEM_GENERIC_SPINLOCK) += rwsem-spinlock.o
lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
lib-$(CONFIG_SEMAPHORE_SLEEPERS) += semaphore-sleepers.o
+lib-$(CONFIG_GENERIC_FIND_FIRST_BIT) += find_next_bit.o
lib-$(CONFIG_GENERIC_FIND_NEXT_BIT) += find_next_bit.o
obj-$(CONFIG_GENERIC_HWEIGHT) += hweight.o
obj-$(CONFIG_LOCK_KERNEL) += kernel_lock.o
diff --git a/lib/find_next_bit.c b/lib/find_next_bit.c
index ce94c4c..d3f5784 100644
--- a/lib/find_next_bit.c
+++ b/lib/find_next_bit.c
@@ -16,6 +16,7 @@

#define BITOP_WORD(nr) ((nr) / BITS_PER_LONG)

+#ifdef CONFIG_GENERIC_FIND_NEXT_BIT
/*
* Find the next set bit in a memory region.
*/
@@ -102,6 +103,63 @@ found_middle:
return result + ffz(tmp);
}
EXPORT_SYMBOL(__find_next_zero_bit);
+#endif /* CONFIG_GENERIC_FIND_NEXT_BIT */
+
+#ifdef CONFIG_GENERIC_FIND_FIRST_BIT
+/*
+ * Find the first set bit in a memory region.
+ */
+unsigned long __find_first_bit(const unsigned long *addr,
+ unsigned long size)
+{
+ const unsigned long *p = addr;
+ unsigned long result = 0;
+ unsigned long tmp;
+
+ while (size & ~(BITS_PER_LONG-1)) {
+ if ((tmp = *(p++)))
+ goto found;
+ result += BITS_PER_LONG;
+ size -= BITS_PER_LONG;
+ }
+ if (!size)
+ return result;
+
+ tmp = (*p) & (~0UL >> (BITS_PER_LONG - size));
+ if (tmp == 0UL) /* Are any bits set? */
+ return result + size; /* Nope. */
+found:
+ return result + __ffs(tmp);
+}
+EXPORT_SYMBOL(__find_first_bit);
+
+/*
+ * Find the first cleared bit in a memory region.
+ */
+unsigned long __find_first_zero_bit(const unsigned long *addr,
+ unsigned long size)
+{
+ const unsigned long *p = addr;
+ unsigned long result = 0;
+ unsigned long tmp;
+
+ while (size & ~(BITS_PER_LONG-1)) {
+ if (~(tmp = *(p++)))
+ goto found;
+ result += BITS_PER_LONG;
+ size -= BITS_PER_LONG;
+ }
+ if (!size)
+ return result;
+
+ tmp = (*p) | (~0UL << size);
+ if (tmp == ~0UL) /* Are any bits zero? */
+ return result + size; /* Nope. */
+found:
+ return result + ffz(tmp);
+}
+EXPORT_SYMBOL(__find_first_zero_bit);
+#endif /* CONFIG_GENERIC_FIND_FIRST_BIT */

#ifdef __BIG_ENDIAN


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