path: root/lib/find_bit.c (plain)
blob: 18072ea9c20ebba59aaa3fdf69ee6bfc1db395b6

1	/* bit search implementation
2	*
3	* Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
4	* Written by David Howells (dhowells@redhat.com)
5	*
6	* Copyright (C) 2008 IBM Corporation
7	* 'find_last_bit' is written by Rusty Russell <rusty@rustcorp.com.au>
8	* (Inspired by David Howell's find_next_bit implementation)
9	*
10	* Rewritten by Yury Norov <yury.norov@gmail.com> to decrease
11	* size and improve performance, 2015.
12	*
13	* This program is free software; you can redistribute it and/or
14	* modify it under the terms of the GNU General Public License
15	* as published by the Free Software Foundation; either version
16	* 2 of the License, or (at your option) any later version.
17	*/
18
19	#include <linux/bitops.h>
20	#include <linux/bitmap.h>
21	#include <linux/export.h>
22	#include <linux/kernel.h>
23
24	#if !defined(find_next_bit) || !defined(find_next_zero_bit)
25
26	/*
27	* This is a common helper function for find_next_bit and
28	* find_next_zero_bit. The difference is the "invert" argument, which
29	* is XORed with each fetched word before searching it for one bits.
30	*/
31	static unsigned long _find_next_bit(const unsigned long *addr,
32	unsigned long nbits, unsigned long start, unsigned long invert)
33	{
34	unsigned long tmp;
35
36	if (!nbits || start >= nbits)
37	return nbits;
38
39	tmp = addr[start / BITS_PER_LONG] ^ invert;
40
41	/* Handle 1st word. */
42	tmp &= BITMAP_FIRST_WORD_MASK(start);
43	start = round_down(start, BITS_PER_LONG);
44
45	while (!tmp) {
46	start += BITS_PER_LONG;
47	if (start >= nbits)
48	return nbits;
49
50	tmp = addr[start / BITS_PER_LONG] ^ invert;
51	}
52
53	return min(start + __ffs(tmp), nbits);
54	}
55	#endif
56
57	#ifndef find_next_bit
58	/*
59	* Find the next set bit in a memory region.
60	*/
61	unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
62	unsigned long offset)
63	{
64	return _find_next_bit(addr, size, offset, 0UL);
65	}
66	EXPORT_SYMBOL(find_next_bit);
67	#endif
68
69	#ifndef find_next_zero_bit
70	unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
71	unsigned long offset)
72	{
73	return _find_next_bit(addr, size, offset, ~0UL);
74	}
75	EXPORT_SYMBOL(find_next_zero_bit);
76	#endif
77
78	#ifndef find_first_bit
79	/*
80	* Find the first set bit in a memory region.
81	*/
82	unsigned long find_first_bit(const unsigned long *addr, unsigned long size)
83	{
84	unsigned long idx;
85
86	for (idx = 0; idx * BITS_PER_LONG < size; idx++) {
87	if (addr[idx])
88	return min(idx * BITS_PER_LONG + __ffs(addr[idx]), size);
89	}
90
91	return size;
92	}
93	EXPORT_SYMBOL(find_first_bit);
94	#endif
95
96	#ifndef find_first_zero_bit
97	/*
98	* Find the first cleared bit in a memory region.
99	*/
100	unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size)
101	{
102	unsigned long idx;
103
104	for (idx = 0; idx * BITS_PER_LONG < size; idx++) {
105	if (addr[idx] != ~0UL)
106	return min(idx * BITS_PER_LONG + ffz(addr[idx]), size);
107	}
108
109	return size;
110	}
111	EXPORT_SYMBOL(find_first_zero_bit);
112	#endif
113
114	#ifndef find_last_bit
115	unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
116	{
117	if (size) {
118	unsigned long val = BITMAP_LAST_WORD_MASK(size);
119	unsigned long idx = (size-1) / BITS_PER_LONG;
120
121	do {
122	val &= addr[idx];
123	if (val)
124	return idx * BITS_PER_LONG + __fls(val);
125
126	val = ~0ul;
127	} while (idx--);
128	}
129	return size;
130	}
131	EXPORT_SYMBOL(find_last_bit);
132	#endif
133
134	#ifdef __BIG_ENDIAN
135
136	/* include/linux/byteorder does not support "unsigned long" type */
137	static inline unsigned long ext2_swab(const unsigned long y)
138	{
139	#if BITS_PER_LONG == 64
140	return (unsigned long) __swab64((u64) y);
141	#elif BITS_PER_LONG == 32
142	return (unsigned long) __swab32((u32) y);
143	#else
144	#error BITS_PER_LONG not defined
145	#endif
146	}
147
148	#if !defined(find_next_bit_le) || !defined(find_next_zero_bit_le)
149	static unsigned long _find_next_bit_le(const unsigned long *addr,
150	unsigned long nbits, unsigned long start, unsigned long invert)
151	{
152	unsigned long tmp;
153
154	if (!nbits || start >= nbits)
155	return nbits;
156
157	tmp = addr[start / BITS_PER_LONG] ^ invert;
158
159	/* Handle 1st word. */
160	tmp &= ext2_swab(BITMAP_FIRST_WORD_MASK(start));
161	start = round_down(start, BITS_PER_LONG);
162
163	while (!tmp) {
164	start += BITS_PER_LONG;
165	if (start >= nbits)
166	return nbits;
167
168	tmp = addr[start / BITS_PER_LONG] ^ invert;
169	}
170
171	return min(start + __ffs(ext2_swab(tmp)), nbits);
172	}
173	#endif
174
175	#ifndef find_next_zero_bit_le
176	unsigned long find_next_zero_bit_le(const void *addr, unsigned
177	long size, unsigned long offset)
178	{
179	return _find_next_bit_le(addr, size, offset, ~0UL);
180	}
181	EXPORT_SYMBOL(find_next_zero_bit_le);
182	#endif
183
184	#ifndef find_next_bit_le
185	unsigned long find_next_bit_le(const void *addr, unsigned
186	long size, unsigned long offset)
187	{
188	return _find_next_bit_le(addr, size, offset, 0UL);
189	}
190	EXPORT_SYMBOL(find_next_bit_le);
191	#endif
192
193	#endif /* __BIG_ENDIAN */
194