| Message ID | 1253726926-5504-2-git-send-email-tabbott@ksplice.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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. -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, 24 Sep 2009, Rusty Russell wrote: > On Thu, 24 Sep 2009 02:58:45 am Tim Abbott wrote: > > +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. You are quite right. -Tim Abbott -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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) { + mid = (start + end) / 2; + result = cmp(key, base + mid * size); + if (result < 0) + end = mid - 1; + else if (result > 0) + start = mid + 1; + else + return (void *)base + mid * size; + } + + return NULL; +} +EXPORT_SYMBOL(bsearch);
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