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