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 */
18static 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 */
25static 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 */
33bool 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 */
81bool 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