[PATCH] Bit operations

[PATCH] Bit operations

[dhowells]

The attached patch provides an out-of-line implementation of find_next_bit()
and rearranges linux/bitops.h to avoid a dependency loop between inline
functions in there and in asm/bitops.h trying to include one another.

Signed-Off-By: dhowells@redhat.com
---
diffstat bitops-2610rc1mm3.diff
 include/linux/bitops.h |    3 +-
 lib/Makefile           |    1 
 lib/find_next_bit.c    |   55 +++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 58 insertions(+), 1 deletion(-)

diff -uNrp /warthog/kernels/linux-2.6.10-rc1-mm3/include/linux/bitops.h linux-2.6.10-rc1-mm3-frv/include/linux/bitops.h
--- /warthog/kernels/linux-2.6.10-rc1-mm3/include/linux/bitops.h	2004-06-18 13:42:16.000000000 +0100
+++ linux-2.6.10-rc1-mm3-frv/include/linux/bitops.h	2004-11-05 14:13:04.362457008 +0000
@@ -1,7 +1,6 @@
 #ifndef _LINUX_BITOPS_H
 #define _LINUX_BITOPS_H
 #include <asm/types.h>
-#include <asm/bitops.h>
 
 /*
  * ffs: find first bit set. This is defined the same way as
@@ -71,6 +70,8 @@ extern __inline__ int generic_fls(int x)
 	return r;
 }
 
+#include <asm/bitops.h>
+
 extern __inline__ int get_bitmask_order(unsigned int count)
 {
 	int order;
diff -uNrp /warthog/kernels/linux-2.6.10-rc1-mm3/lib/find_next_bit.c linux-2.6.10-rc1-mm3-frv/lib/find_next_bit.c
--- /warthog/kernels/linux-2.6.10-rc1-mm3/lib/find_next_bit.c	1970-01-01 01:00:00.000000000 +0100
+++ linux-2.6.10-rc1-mm3-frv/lib/find_next_bit.c	2004-11-05 14:13:04.571439356 +0000
@@ -0,0 +1,55 @@
+/* find_next_bit.c: fallback find next bit implementation
+ *
+ * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/bitops.h>
+
+int find_next_bit(const unsigned long *addr, int size, int offset)
+{
+	const unsigned long *base;
+	const int NBITS = sizeof(*addr) * 8;
+	unsigned long tmp;
+
+	base = addr;
+	if (offset) {
+		int suboffset;
+
+		addr += offset / NBITS;
+
+		suboffset = offset % NBITS;
+		if (suboffset) {
+			tmp = *addr;
+			tmp >>= suboffset;
+			if (tmp)
+				goto finish;
+		}
+
+		addr++;
+	}
+
+	while ((tmp = *addr) == 0)
+		addr++;
+
+	offset = (addr - base) * NBITS;
+
+ finish:
+	/* count the remaining bits without using __ffs() since that takes a 32-bit arg */
+	while (!(tmp & 0xff)) {
+		offset += 8;
+		tmp >>= 8;
+	}
+
+	while (!(tmp & 1)) {
+		offset++;
+		tmp >>= 1;
+	}
+
+	return offset;
+}
diff -uNrp /warthog/kernels/linux-2.6.10-rc1-mm3/lib/Makefile linux-2.6.10-rc1-mm3-frv/lib/Makefile
--- /warthog/kernels/linux-2.6.10-rc1-mm3/lib/Makefile	2004-11-05 13:15:52.000000000 +0000
+++ linux-2.6.10-rc1-mm3-frv/lib/Makefile	2004-11-05 14:13:04.574439103 +0000
@@ -14,6 +14,7 @@ endif
 
 lib-$(CONFIG_RWSEM_GENERIC_SPINLOCK) += rwsem-spinlock.o
 lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
+lib-$(CONFIG_GENERIC_FIND_NEXT_BIT) += find_next_bit.o
 obj-$(CONFIG_LOCK_KERNEL) += kernel_lock.o
 
 ifneq ($(CONFIG_HAVE_DEC_LOCK),y) 

Re: [PATCH] Bit operations

[David Howells]

Hi Andrew,

> The attached patch provides an out-of-line implementation of find_next_bit()
> and rearranges linux/bitops.h to avoid a dependency loop between inline
> functions in there and in asm/bitops.h trying to include one another.

Is there any reason you dropped the part of this patch that rearranged
linux/bitops.h? asm/bitops.h may need generic_ffs() for implementing
sched_find_first_bit(), and obviously asm/bitops.h can't include
linux/bitops.h.

David

Re: [PATCH] Bit operations

[Andrew Morton]

David Howells <dhowells@redhat.com> wrote:
>
> 
> Hi Andrew,
> 
> > The attached patch provides an out-of-line implementation of find_next_bit()
> > and rearranges linux/bitops.h to avoid a dependency loop between inline
> > functions in there and in asm/bitops.h trying to include one another.
> 
> Is there any reason you dropped the part of this patch that rearranged
> linux/bitops.h? asm/bitops.h may need generic_ffs() for implementing
> sched_find_first_bit(), and obviously asm/bitops.h can't include
> linux/bitops.h.

I was doing a reject fixup and restored the thing back in what seemed a
better place.  Of course, had it been commented, that wouldn't have
happened.  It is commented now.