From 1a94dc35bc5c166d89913dc01a49d27a3c21a455 Mon Sep 17 00:00:00 2001 From: Tim Abbott Date: Thu, 14 Apr 2011 20:00:19 +0200 Subject: lib: Add generic binary search function to the kernel. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Extra-bikeshedding-by: Alan Jenkins Extra-bikeshedding-by: André Goddard Rosa Extra-bikeshedding-by: Rusty Russell Signed-off-by: Rusty Russell Signed-off-by: Alessio Igor Bogani Signed-off-by: Rusty Russell --- lib/bsearch.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 53 insertions(+) create mode 100644 lib/bsearch.c (limited to 'lib/bsearch.c') diff --git a/lib/bsearch.c b/lib/bsearch.c new file mode 100644 index 00000000000..5b54758e2af --- /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 + * + * 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 +#include + +/* + * 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; + else + return (void *)base + mid * size; + } + + return NULL; +} +EXPORT_SYMBOL(bsearch); -- cgit v1.2.3-18-g5258