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    SubjectRe: [PATCH 1/2] lib: Add generic binary search function to the kernel.
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    On Thu, 24 Sep 2009 02:58:45 am Tim Abbott wrote:
    > There a large number hand-coded binary searches in the kernel (run
    > "git grep search | grep binary" to find many of them). Since in my
    > experience, hand-coding binary searches can be error-prone, it seems
    > worth cleaning this up by providing a generic binary search function.
    >
    > This generic binary search implementation comes from Ksplice. It has
    > the same basic API as the C library bsearch() function. Ksplice uses
    > it in half a dozen places with 4 different comparison functions, and I
    > think our code is substantially cleaner because of this.
    >
    > Signed-off-by: Tim Abbott <tabbott@ksplice.com>
    > ---
    > include/linux/bsearch.h | 9 ++++++++
    > lib/Makefile | 2 +-
    > lib/bsearch.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++
    > 3 files changed, 63 insertions(+), 1 deletions(-)
    > create mode 100644 include/linux/bsearch.h
    > create mode 100644 lib/bsearch.c
    >
    > diff --git a/include/linux/bsearch.h b/include/linux/bsearch.h
    > new file mode 100644
    > index 0000000..90b1aa8
    > --- /dev/null
    > +++ b/include/linux/bsearch.h
    > @@ -0,0 +1,9 @@
    > +#ifndef _LINUX_BSEARCH_H
    > +#define _LINUX_BSEARCH_H
    > +
    > +#include <linux/types.h>
    > +
    > +void *bsearch(const void *key, const void *base, size_t num, size_t size,
    > + int (*cmp)(const void *key, const void *elt));
    > +
    > +#endif /* _LINUX_BSEARCH_H */
    > diff --git a/lib/Makefile b/lib/Makefile
    > index 2e78277..fb60af1 100644
    > --- a/lib/Makefile
    > +++ b/lib/Makefile
    > @@ -21,7 +21,7 @@ lib-y += kobject.o kref.o klist.o
    >
    > obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
    > bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \
    > - string_helpers.o gcd.o
    > + string_helpers.o gcd.o bsearch.o
    >
    > ifeq ($(CONFIG_DEBUG_KOBJECT),y)
    > CFLAGS_kobject.o += -DDEBUG
    > diff --git a/lib/bsearch.c b/lib/bsearch.c
    > new file mode 100644
    > index 0000000..4297c98
    > --- /dev/null
    > +++ b/lib/bsearch.c
    > @@ -0,0 +1,53 @@
    > +/*
    > + * A generic implementation of binary search for the Linux kernel
    > + *
    > + * Copyright (C) 2008-2009 Ksplice, Inc.
    > + * Author: Tim Abbott <tabbott@ksplice.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; version 2.
    > + */
    > +
    > +#include <linux/module.h>
    > +#include <linux/bsearch.h>
    > +
    > +/*
    > + * bsearch - binary search an array of elements
    > + * @key: pointer to item being searched for
    > + * @base: pointer to data to sort
    > + * @num: number of elements
    > + * @size: size of each element
    > + * @cmp: pointer to comparison function
    > + *
    > + * This function does a binary search on the given array. The
    > + * contents of the array should already be in ascending sorted order
    > + * under the provided comparison function.
    > + *
    > + * Note that the key need not have the same type as the elements in
    > + * the array, e.g. key could be a string and the comparison function
    > + * could compare the string with the struct's name field. However, if
    > + * the key and elements in the array are of the same type, you can use
    > + * the same comparison function for both sort() and bsearch().
    > + */
    > +void *bsearch(const void *key, const void *base, size_t num, size_t size,
    > + int (*cmp)(const void *key, const void *elt))
    > +{
    > + int start = 0, end = num - 1, mid, result;
    > + if (num == 0)
    > + return NULL;
    > +
    > + while (start <= end) {

    The if (num == 0) line is superfluous.

    But I'd be happy to take this as part of Alan's patches.

    Thanks!
    Rusty.


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