bitfunc.c revision e8b8e97f
1// SPDX-License-Identifier: GPL-2.0
2/*
3 *
4 * Copyright (C) 2019-2021 Paragon Software GmbH, All rights reserved.
5 *
6 */
7
8#include <linux/blkdev.h>
9#include <linux/buffer_head.h>
10#include <linux/fs.h>
11#include <linux/nls.h>
12
13#include "debug.h"
14#include "ntfs.h"
15#include "ntfs_fs.h"
16
17#define BITS_IN_SIZE_T (sizeof(size_t) * 8)
18
19/*
20 * fill_mask[i] - first i bits are '1' , i = 0,1,2,3,4,5,6,7,8
21 * fill_mask[i] = 0xFF >> (8-i)
22 */
23static const u8 fill_mask[] = { 0x00, 0x01, 0x03, 0x07, 0x0F,
24				0x1F, 0x3F, 0x7F, 0xFF };
25
26/*
27 * zero_mask[i] - first i bits are '0' , i = 0,1,2,3,4,5,6,7,8
28 * zero_mask[i] = 0xFF << i
29 */
30static const u8 zero_mask[] = { 0xFF, 0xFE, 0xFC, 0xF8, 0xF0,
31				0xE0, 0xC0, 0x80, 0x00 };
32
33/*
34 * are_bits_clear
35 *
36 * Return: True if all bits [bit, bit+nbits) are zeros "0".
37 */
38bool are_bits_clear(const ulong *lmap, size_t bit, size_t nbits)
39{
40	size_t pos = bit & 7;
41	const u8 *map = (u8 *)lmap + (bit >> 3);
42
43	if (pos) {
44		if (8 - pos >= nbits)
45			return !nbits || !(*map & fill_mask[pos + nbits] &
46					   zero_mask[pos]);
47
48		if (*map++ & zero_mask[pos])
49			return false;
50		nbits -= 8 - pos;
51	}
52
53	pos = ((size_t)map) & (sizeof(size_t) - 1);
54	if (pos) {
55		pos = sizeof(size_t) - pos;
56		if (nbits >= pos * 8) {
57			for (nbits -= pos * 8; pos; pos--, map++) {
58				if (*map)
59					return false;
60			}
61		}
62	}
63
64	for (pos = nbits / BITS_IN_SIZE_T; pos; pos--, map += sizeof(size_t)) {
65		if (*((size_t *)map))
66			return false;
67	}
68
69	for (pos = (nbits % BITS_IN_SIZE_T) >> 3; pos; pos--, map++) {
70		if (*map)
71			return false;
72	}
73
74	pos = nbits & 7;
75	if (pos && (*map & fill_mask[pos]))
76		return false;
77
78	return true;
79}
80
81/*
82 * are_bits_set
83 *
84 * Return: True if all bits [bit, bit+nbits) are ones "1".
85 */
86bool are_bits_set(const ulong *lmap, size_t bit, size_t nbits)
87{
88	u8 mask;
89	size_t pos = bit & 7;
90	const u8 *map = (u8 *)lmap + (bit >> 3);
91
92	if (pos) {
93		if (8 - pos >= nbits) {
94			mask = fill_mask[pos + nbits] & zero_mask[pos];
95			return !nbits || (*map & mask) == mask;
96		}
97
98		mask = zero_mask[pos];
99		if ((*map++ & mask) != mask)
100			return false;
101		nbits -= 8 - pos;
102	}
103
104	pos = ((size_t)map) & (sizeof(size_t) - 1);
105	if (pos) {
106		pos = sizeof(size_t) - pos;
107		if (nbits >= pos * 8) {
108			for (nbits -= pos * 8; pos; pos--, map++) {
109				if (*map != 0xFF)
110					return false;
111			}
112		}
113	}
114
115	for (pos = nbits / BITS_IN_SIZE_T; pos; pos--, map += sizeof(size_t)) {
116		if (*((size_t *)map) != MINUS_ONE_T)
117			return false;
118	}
119
120	for (pos = (nbits % BITS_IN_SIZE_T) >> 3; pos; pos--, map++) {
121		if (*map != 0xFF)
122			return false;
123	}
124
125	pos = nbits & 7;
126	if (pos) {
127		u8 mask = fill_mask[pos];
128
129		if ((*map & mask) != mask)
130			return false;
131	}
132
133	return true;
134}
135