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