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Subject[PATCH v5 1/3] lib: find_*_bit reimplementation
Date
New implementations takes less space in source file (see diffstat)
and in object. For me it's 710 vs 453 bytes of text.
It also shows better performance.

find_last_bit description fixed due to obvious typo.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
include/linux/bitops.h | 4 +-
lib/find_last_bit.c | 35 +++----
lib/find_next_bit.c | 267 ++++++++++++++-----------------------------------
3 files changed, 90 insertions(+), 216 deletions(-)

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 5d858e0..297f5bd 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -218,9 +218,9 @@ static inline unsigned long __ffs64(u64 word)
/**
* find_last_bit - find the last set bit in a memory region
* @addr: The address to start the search at
- * @size: The maximum size to search
+ * @size: The number of bits to search
*
- * Returns the bit number of the first set bit, or size.
+ * Returns the bit number of the last set bit, or size.
*/
extern unsigned long find_last_bit(const unsigned long *addr,
unsigned long size);
diff --git a/lib/find_last_bit.c b/lib/find_last_bit.c
index 91ca09f..f7b594e 100644
--- a/lib/find_last_bit.c
+++ b/lib/find_last_bit.c
@@ -4,6 +4,9 @@
* Written by Rusty Russell <rusty@rustcorp.com.au>
* (Inspired by David Howell's find_next_bit implementation)
*
+ * Rewritten by Yury Norov <yury.norov@gmail.com> to decrease
+ * size and improve performance, 2015.
+ *
* 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
@@ -12,36 +15,24 @@

#include <linux/bitops.h>
#include <linux/export.h>
-#include <asm/types.h>
-#include <asm/byteorder.h>
+#include <linux/kernel.h>

#ifndef find_last_bit

unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
{
- unsigned long words;
- unsigned long tmp;
-
- /* Start at final word. */
- words = size / BITS_PER_LONG;
+ if (size) {
+ unsigned long val = BITMAP_LAST_WORD_MASK(size);
+ unsigned long idx = (size-1) / BITS_PER_LONG;

- /* Partial final word? */
- if (size & (BITS_PER_LONG-1)) {
- tmp = (addr[words] & (~0UL >> (BITS_PER_LONG
- - (size & (BITS_PER_LONG-1)))));
- if (tmp)
- goto found;
- }
+ do {
+ val &= addr[idx];
+ if (val)
+ return idx * BITS_PER_LONG + __fls(val);

- while (words) {
- tmp = addr[--words];
- if (tmp) {
-found:
- return words * BITS_PER_LONG + __fls(tmp);
- }
+ val = ~0ul;
+ } while (idx--);
}
-
- /* Not found */
return size;
}
EXPORT_SYMBOL(find_last_bit);
diff --git a/lib/find_next_bit.c b/lib/find_next_bit.c
index 0cbfc0b..cbea5ef 100644
--- a/lib/find_next_bit.c
+++ b/lib/find_next_bit.c
@@ -3,6 +3,9 @@
* Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
+ * Rewritten by Yury Norov <yury.norov@gmail.com> to decrease
+ * size and improve performance, 2015.
+ *
* 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
@@ -11,98 +14,58 @@

#include <linux/bitops.h>
#include <linux/export.h>
-#include <asm/types.h>
-#include <asm/byteorder.h>
+#include <linux/kernel.h>

-#define BITOP_WORD(nr) ((nr) / BITS_PER_LONG)
+#if !defined(find_next_bit) || !defined(find_next_zero_bit)

-#ifndef find_next_bit
/*
- * Find the next set bit in a memory region.
+ * This is a common helper function for find_next_bit and
+ * find_next_zero_bit. The difference is the "invert" argument, which
+ * is XORed with each fetched word before searching it for one bits.
*/
-unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
- unsigned long offset)
+static unsigned long _find_next_bit(const unsigned long *addr,
+ unsigned long nbits, unsigned long start, unsigned long invert)
{
- 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 (!nbits || start >= nbits)
+ return nbits;
+
+ tmp = addr[start / BITS_PER_LONG] ^ invert;
+
+ /* Handle 1st word. */
+ tmp &= BITMAP_FIRST_WORD_MASK(start);
+ start = round_down(start, BITS_PER_LONG);
+
+ while (!tmp) {
+ start += BITS_PER_LONG;
+ if (start >= nbits)
+ return nbits;
+
+ tmp = addr[start / BITS_PER_LONG] ^ invert;
}
- 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);
+ return min(start + __ffs(tmp), nbits);
}
-EXPORT_SYMBOL(find_next_bit);
#endif

-#ifndef find_next_zero_bit
+#ifndef find_next_bit
/*
- * This implementation of find_{first,next}_zero_bit was stolen from
- * Linus' asm-alpha/bitops.h.
+ * Find the next set bit in a memory region.
*/
+unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
+ unsigned long offset)
+{
+ return _find_next_bit(addr, size, offset, 0UL);
+}
+EXPORT_SYMBOL(find_next_bit);
+#endif
+
+#ifndef find_next_zero_bit
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);
+ return _find_next_bit(addr, size, offset, ~0UL);
}
EXPORT_SYMBOL(find_next_zero_bit);
#endif
@@ -113,24 +76,14 @@ EXPORT_SYMBOL(find_next_zero_bit);
*/
unsigned long find_first_bit(const unsigned long *addr, unsigned long size)
{
- const unsigned long *p = addr;
- unsigned long result = 0;
- unsigned long tmp;
+ unsigned long idx;

- while (size & ~(BITS_PER_LONG-1)) {
- if ((tmp = *(p++)))
- goto found;
- result += BITS_PER_LONG;
- size -= BITS_PER_LONG;
+ for (idx = 0; idx * BITS_PER_LONG < size; idx++) {
+ if (addr[idx])
+ return min(idx * BITS_PER_LONG + __ffs(addr[idx]), size);
}
- 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);
+ return size;
}
EXPORT_SYMBOL(find_first_bit);
#endif
@@ -141,24 +94,14 @@ EXPORT_SYMBOL(find_first_bit);
*/
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;
+ unsigned long idx;

- while (size & ~(BITS_PER_LONG-1)) {
- if (~(tmp = *(p++)))
- goto found;
- result += BITS_PER_LONG;
- size -= BITS_PER_LONG;
+ for (idx = 0; idx * BITS_PER_LONG < size; idx++) {
+ if (addr[idx] != ~0UL)
+ return min(idx * BITS_PER_LONG + ffz(addr[idx]), size);
}
- if (!size)
- return result;

- tmp = (*p) | (~0UL << size);
- if (tmp == ~0UL) /* Are any bits zero? */
- return result + size; /* Nope. */
-found:
- return result + ffz(tmp);
+ return size;
}
EXPORT_SYMBOL(find_first_zero_bit);
#endif
@@ -166,18 +109,6 @@ EXPORT_SYMBOL(find_first_zero_bit);
#ifdef __BIG_ENDIAN

/* include/linux/byteorder does not support "unsigned long" type */
-static inline unsigned long ext2_swabp(const unsigned long * x)
-{
-#if BITS_PER_LONG == 64
- return (unsigned long) __swab64p((u64 *) x);
-#elif BITS_PER_LONG == 32
- return (unsigned long) __swab32p((u32 *) x);
-#else
-#error BITS_PER_LONG not defined
-#endif
-}
-
-/* include/linux/byteorder doesn't support "unsigned long" type */
static inline unsigned long ext2_swab(const unsigned long y)
{
#if BITS_PER_LONG == 64
@@ -189,48 +120,38 @@ static inline unsigned long ext2_swab(const unsigned long y)
#endif
}

-#ifndef find_next_zero_bit_le
-unsigned long find_next_zero_bit_le(const void *addr, unsigned
- long size, unsigned long offset)
+#if !defined(find_next_bit_le) || !defined(find_next_zero_bit_le)
+static unsigned long _find_next_bit_le(const unsigned long *addr,
+ unsigned long nbits, unsigned long start, unsigned long invert)
{
- const unsigned long *p = addr;
- unsigned long result = offset & ~(BITS_PER_LONG - 1);
unsigned long tmp;

- if (offset >= size)
- return size;
- p += BITOP_WORD(offset);
- size -= result;
- offset &= (BITS_PER_LONG - 1UL);
- if (offset) {
- tmp = ext2_swabp(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;
- }
+ if (!nbits || start >= nbits)
+ return nbits;
+
+ tmp = addr[start / BITS_PER_LONG] ^ invert;
+
+ /* Handle 1st word. */
+ tmp &= ext2_swab(BITMAP_FIRST_WORD_MASK(start));
+ start = round_down(start, BITS_PER_LONG);

- while (size & ~(BITS_PER_LONG - 1)) {
- if (~(tmp = *(p++)))
- goto found_middle_swap;
- result += BITS_PER_LONG;
- size -= BITS_PER_LONG;
+ while (!tmp) {
+ start += BITS_PER_LONG;
+ if (start >= nbits)
+ return nbits;
+
+ tmp = addr[start / BITS_PER_LONG] ^ invert;
}
- if (!size)
- return result;
- tmp = ext2_swabp(p);
-found_first:
- tmp |= ~0UL << size;
- if (tmp == ~0UL) /* Are any bits zero? */
- return result + size; /* Nope. Skip ffz */
-found_middle:
- return result + ffz(tmp);

-found_middle_swap:
- return result + ffz(ext2_swab(tmp));
+ return min(start + __ffs(ext2_swab(tmp)), nbits);
+}
+#endif
+
+#ifndef find_next_zero_bit_le
+unsigned long find_next_zero_bit_le(const void *addr, unsigned
+ long size, unsigned long offset)
+{
+ return _find_next_bit_le(addr, size, offset, ~0UL);
}
EXPORT_SYMBOL(find_next_zero_bit_le);
#endif
@@ -239,45 +160,7 @@ EXPORT_SYMBOL(find_next_zero_bit_le);
unsigned long find_next_bit_le(const void *addr, unsigned
long size, unsigned long offset)
{
- const unsigned long *p = addr;
- unsigned long result = offset & ~(BITS_PER_LONG - 1);
- unsigned long tmp;
-
- if (offset >= size)
- return size;
- p += BITOP_WORD(offset);
- size -= result;
- offset &= (BITS_PER_LONG - 1UL);
- if (offset) {
- tmp = ext2_swabp(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)) {
- tmp = *(p++);
- if (tmp)
- goto found_middle_swap;
- result += BITS_PER_LONG;
- size -= BITS_PER_LONG;
- }
- if (!size)
- return result;
- tmp = ext2_swabp(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);
-
-found_middle_swap:
- return result + __ffs(ext2_swab(tmp));
+ return _find_next_bit_le(addr, size, offset, 0UL);
}
EXPORT_SYMBOL(find_next_bit_le);
#endif
--
2.1.0


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