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}