Eric Lee / smarc-ti-linux-kernel

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Commit 1a94dc35bc5c166d89913dc01a49d27a3c21a455

Authored by Tim Abbott
Committed by Rusty Russell
1 parent f02e8a6596

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: Tim Abbott <tabbott@ksplice.com>
Extra-bikeshedding-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Extra-bikeshedding-by: André Goddard Rosa <andre.goddard@gmail.com>
Extra-bikeshedding-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Alessio Igor Bogani <abogani@kernel.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Showing 3 changed files with 64 additions and 1 deletions Side-by-side Diff

include/linux/bsearch.h
Diff comments   View file @ 1a94dc3
  1 +#ifndef _LINUX_BSEARCH_H
  2 +#define _LINUX_BSEARCH_H
  3 +
  4 +#include <linux/types.h>
  5 +
  6 +void *bsearch(const void *key, const void *base, size_t num, size_t size,
  7 + int (*cmp)(const void *key, const void *elt));
  8 +
  9 +#endif /* _LINUX_BSEARCH_H */
... ... @@ -21,7 +21,8 @@
21 21  
22 22 obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
23 23 bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \
24   - string_helpers.o gcd.o lcm.o list_sort.o uuid.o flex_array.o
  24 + string_helpers.o gcd.o lcm.o list_sort.o uuid.o flex_array.o \
  25 + bsearch.o
25 26 obj-y += kstrtox.o
26 27 obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
27 28  
  1 +/*
  2 + * A generic implementation of binary search for the Linux kernel
  3 + *
  4 + * Copyright (C) 2008-2009 Ksplice, Inc.
  5 + * Author: Tim Abbott <tabbott@ksplice.com>
  6 + *
  7 + * This program is free software; you can redistribute it and/or
  8 + * modify it under the terms of the GNU General Public License as
  9 + * published by the Free Software Foundation; version 2.
  10 + */
  11 +
  12 +#include <linux/module.h>
  13 +#include <linux/bsearch.h>
  14 +
  15 +/*
  16 + * bsearch - binary search an array of elements
  17 + * @key: pointer to item being searched for
  18 + * @base: pointer to first element to search
  19 + * @num: number of elements
  20 + * @size: size of each element
  21 + * @cmp: pointer to comparison function
  22 + *
  23 + * This function does a binary search on the given array. The
  24 + * contents of the array should already be in ascending sorted order
  25 + * under the provided comparison function.
  26 + *
  27 + * Note that the key need not have the same type as the elements in
  28 + * the array, e.g. key could be a string and the comparison function
  29 + * could compare the string with the struct's name field. However, if
  30 + * the key and elements in the array are of the same type, you can use
  31 + * the same comparison function for both sort() and bsearch().
  32 + */
  33 +void *bsearch(const void *key, const void *base, size_t num, size_t size,
  34 + int (*cmp)(const void *key, const void *elt))
  35 +{
  36 + size_t start = 0, end = num;
  37 + int result;
  38 +
  39 + while (start < end) {
  40 + size_t mid = start + (end - start) / 2;
  41 +
  42 + result = cmp(key, base + mid * size);
  43 + if (result < 0)
  44 + end = mid;
  45 + else if (result > 0)
  46 + start = mid + 1;
  47 + else
  48 + return (void *)base + mid * size;
  49 + }
  50 +
  51 + return NULL;
  52 +}
  53 +EXPORT_SYMBOL(bsearch);