1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
|
// SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
/* Copyright (c) 2016-2018, NXP Semiconductors
* Copyright (c) 2018-2019, Vladimir Oltean <olteanv@gmail.com>
*/
#include <linux/packing.h>
#include <linux/module.h>
#include <linux/bitops.h>
#include <linux/errno.h>
#include <linux/types.h>
static int get_le_offset(int offset)
{
int closest_multiple_of_4;
closest_multiple_of_4 = (offset / 4) * 4;
offset -= closest_multiple_of_4;
return closest_multiple_of_4 + (3 - offset);
}
static int get_reverse_lsw32_offset(int offset, size_t len)
{
int closest_multiple_of_4;
int word_index;
word_index = offset / 4;
closest_multiple_of_4 = word_index * 4;
offset -= closest_multiple_of_4;
word_index = (len / 4) - word_index - 1;
return word_index * 4 + offset;
}
static u64 bit_reverse(u64 val, unsigned int width)
{
u64 new_val = 0;
unsigned int bit;
unsigned int i;
for (i = 0; i < width; i++) {
bit = (val & (1 << i)) != 0;
new_val |= (bit << (width - i - 1));
}
return new_val;
}
static void adjust_for_msb_right_quirk(u64 *to_write, int *box_start_bit,
int *box_end_bit, u8 *box_mask)
{
int box_bit_width = *box_start_bit - *box_end_bit + 1;
int new_box_start_bit, new_box_end_bit;
*to_write >>= *box_end_bit;
*to_write = bit_reverse(*to_write, box_bit_width);
*to_write <<= *box_end_bit;
new_box_end_bit = box_bit_width - *box_start_bit - 1;
new_box_start_bit = box_bit_width - *box_end_bit - 1;
*box_mask = GENMASK_ULL(new_box_start_bit, new_box_end_bit);
*box_start_bit = new_box_start_bit;
*box_end_bit = new_box_end_bit;
}
/**
* packing - Convert numbers (currently u64) between a packed and an unpacked
* format. Unpacked means laid out in memory in the CPU's native
* understanding of integers, while packed means anything else that
* requires translation.
*
* @pbuf: Pointer to a buffer holding the packed value.
* @uval: Pointer to an u64 holding the unpacked value.
* @startbit: The index (in logical notation, compensated for quirks) where
* the packed value starts within pbuf. Must be larger than, or
* equal to, endbit.
* @endbit: The index (in logical notation, compensated for quirks) where
* the packed value ends within pbuf. Must be smaller than, or equal
* to, startbit.
* @op: If PACK, then uval will be treated as const pointer and copied (packed)
* into pbuf, between startbit and endbit.
* If UNPACK, then pbuf will be treated as const pointer and the logical
* value between startbit and endbit will be copied (unpacked) to uval.
* @quirks: A bit mask of QUIRK_LITTLE_ENDIAN, QUIRK_LSW32_IS_FIRST and
* QUIRK_MSB_ON_THE_RIGHT.
*
* Return: 0 on success, EINVAL or ERANGE if called incorrectly. Assuming
* correct usage, return code may be discarded.
* If op is PACK, pbuf is modified.
* If op is UNPACK, uval is modified.
*/
int packing(void *pbuf, u64 *uval, int startbit, int endbit, size_t pbuflen,
enum packing_op op, u8 quirks)
{
/* Number of bits for storing "uval"
* also width of the field to access in the pbuf
*/
u64 value_width;
/* Logical byte indices corresponding to the
* start and end of the field.
*/
int plogical_first_u8, plogical_last_u8, box;
/* startbit is expected to be larger than endbit */
if (startbit < endbit)
/* Invalid function call */
return -EINVAL;
value_width = startbit - endbit + 1;
if (value_width > 64)
return -ERANGE;
/* Check if "uval" fits in "value_width" bits.
* If value_width is 64, the check will fail, but any
* 64-bit uval will surely fit.
*/
if (op == PACK && value_width < 64 && (*uval >= (1ull << value_width)))
/* Cannot store "uval" inside "value_width" bits.
* Truncating "uval" is most certainly not desirable,
* so simply erroring out is appropriate.
*/
return -ERANGE;
/* Initialize parameter */
if (op == UNPACK)
*uval = 0;
/* Iterate through an idealistic view of the pbuf as an u64 with
* no quirks, u8 by u8 (aligned at u8 boundaries), from high to low
* logical bit significance. "box" denotes the current logical u8.
*/
plogical_first_u8 = startbit / 8;
plogical_last_u8 = endbit / 8;
for (box = plogical_first_u8; box >= plogical_last_u8; box--) {
/* Bit indices into the currently accessed 8-bit box */
int box_start_bit, box_end_bit, box_addr;
u8 box_mask;
/* Corresponding bits from the unpacked u64 parameter */
int proj_start_bit, proj_end_bit;
u64 proj_mask;
/* This u8 may need to be accessed in its entirety
* (from bit 7 to bit 0), or not, depending on the
* input arguments startbit and endbit.
*/
if (box == plogical_first_u8)
box_start_bit = startbit % 8;
else
box_start_bit = 7;
if (box == plogical_last_u8)
box_end_bit = endbit % 8;
else
box_end_bit = 0;
/* We have determined the box bit start and end.
* Now we calculate where this (masked) u8 box would fit
* in the unpacked (CPU-readable) u64 - the u8 box's
* projection onto the unpacked u64. Though the
* box is u8, the projection is u64 because it may fall
* anywhere within the unpacked u64.
*/
proj_start_bit = ((box * 8) + box_start_bit) - endbit;
proj_end_bit = ((box * 8) + box_end_bit) - endbit;
proj_mask = GENMASK_ULL(proj_start_bit, proj_end_bit);
box_mask = GENMASK_ULL(box_start_bit, box_end_bit);
/* Determine the offset of the u8 box inside the pbuf,
* adjusted for quirks. The adjusted box_addr will be used for
* effective addressing inside the pbuf (so it's not
* logical any longer).
*/
box_addr = pbuflen - box - 1;
if (quirks & QUIRK_LITTLE_ENDIAN)
box_addr = get_le_offset(box_addr);
if (quirks & QUIRK_LSW32_IS_FIRST)
box_addr = get_reverse_lsw32_offset(box_addr,
pbuflen);
if (op == UNPACK) {
u64 pval;
/* Read from pbuf, write to uval */
pval = ((u8 *)pbuf)[box_addr] & box_mask;
if (quirks & QUIRK_MSB_ON_THE_RIGHT)
adjust_for_msb_right_quirk(&pval,
&box_start_bit,
&box_end_bit,
&box_mask);
pval >>= box_end_bit;
pval <<= proj_end_bit;
*uval &= ~proj_mask;
*uval |= pval;
} else {
u64 pval;
/* Write to pbuf, read from uval */
pval = (*uval) & proj_mask;
pval >>= proj_end_bit;
if (quirks & QUIRK_MSB_ON_THE_RIGHT)
adjust_for_msb_right_quirk(&pval,
&box_start_bit,
&box_end_bit,
&box_mask);
pval <<= box_end_bit;
((u8 *)pbuf)[box_addr] &= ~box_mask;
((u8 *)pbuf)[box_addr] |= pval;
}
}
return 0;
}
EXPORT_SYMBOL(packing);
MODULE_LICENSE("GPL v2");
MODULE_DESCRIPTION("Generic bitfield packing and unpacking");
|
