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Commit 1a94dc35 authored by Tim Abbott's avatar Tim Abbott Committed by Rusty Russell

lib: Add generic binary search function to the kernel.

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: default avatarTim Abbott <>
Extra-bikeshedding-by: default avatarAlan Jenkins <>
Extra-bikeshedding-by: default avatarAndré Goddard Rosa <>
Extra-bikeshedding-by: default avatarRusty Russell <>
Signed-off-by: default avatarRusty Russell <>
Signed-off-by: default avatarAlessio Igor Bogani <>
Signed-off-by: default avatarRusty Russell <>
parent f02e8a65
#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 */
......@@ -21,7 +21,8 @@ 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 lcm.o list_sort.o uuid.o flex_array.o
string_helpers.o gcd.o lcm.o list_sort.o uuid.o flex_array.o \
obj-y += kstrtox.o
obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
* A generic implementation of binary search for the Linux kernel
* Copyright (C) 2008-2009 Ksplice, Inc.
* Author: Tim Abbott <>
* 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 first element to search
* @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))
size_t start = 0, end = num;
int result;
while (start < end) {
size_t mid = start + (end - start) / 2;
result = cmp(key, base + mid * size);
if (result < 0)
end = mid;
else if (result > 0)
start = mid + 1;
return (void *)base + mid * size;
return NULL;
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