From: Tim Abbott <tabbott@xxxxxxxxxxx>
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@xxxxxxxxxxx>
Extra-bikeshedding-by: Alan Jenkins <alan-jenkins@xxxxxxxxxxxxxx>
Extra-bikeshedding-by: Andrà Goddard Rosa <andre.goddard@xxxxxxxxx>
Extra-bikeshedding-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Alessio Igor Bogani <abogani@xxxxxxxxxx>
---
include/linux/bsearch.h | 9 ++++++++
lib/Makefile | 3 +-
lib/bsearch.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 64 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 ef0f285..4b49a24 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -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 \
+ bsearch.o
obj-y += kstrtox.o
obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
diff --git a/lib/bsearch.c b/lib/bsearch.c
new file mode 100644
index 0000000..5b54758
--- /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@xxxxxxxxxxx>
+ *
+ * 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;
+ else
+ return (void *)base + mid * size;
+ }
+
+ return NULL;
+}
+EXPORT_SYMBOL(bsearch);
--
1.7.4.1
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