1/* SPDX-License-Identifier: GPL-2.0 */
2
3#ifndef __842_H__
4#define __842_H__
5
6/* The 842 compressed format is made up of multiple blocks, each of
7 * which have the format:
8 *
9 * <template>[arg1][arg2][arg3][arg4]
10 *
11 * where there are between 0 and 4 template args, depending on the specific
12 * template operation. For normal operations, each arg is either a specific
13 * number of data bytes to add to the output buffer, or an index pointing
14 * to a previously-written number of data bytes to copy to the output buffer.
15 *
16 * The template code is a 5-bit value. This code indicates what to do with
17 * the following data. Template codes from 0 to 0x19 should use the template
18 * table, the static "decomp_ops" table used in decompress. For each template
19 * (table row), there are between 1 and 4 actions; each action corresponds to
20 * an arg following the template code bits. Each action is either a "data"
21 * type action, or a "index" type action, and each action results in 2, 4, or 8
22 * bytes being written to the output buffer. Each template (i.e. all actions
23 * in the table row) will add up to 8 bytes being written to the output buffer.
24 * Any row with less than 4 actions is padded with noop actions, indicated by
25 * N0 (for which there is no corresponding arg in the compressed data buffer).
26 *
27 * "Data" actions, indicated in the table by D2, D4, and D8, mean that the
28 * corresponding arg is 2, 4, or 8 bytes, respectively, in the compressed data
29 * buffer should be copied directly to the output buffer.
30 *
31 * "Index" actions, indicated in the table by I2, I4, and I8, mean the
32 * corresponding arg is an index parameter that points to, respectively, a 2,
33 * 4, or 8 byte value already in the output buffer, that should be copied to
34 * the end of the output buffer. Essentially, the index points to a position
35 * in a ring buffer that contains the last N bytes of output buffer data.
36 * The number of bits for each index's arg are: 8 bits for I2, 9 bits for I4,
37 * and 8 bits for I8. Since each index points to a 2, 4, or 8 byte section,
38 * this means that I2 can reference 512 bytes ((2^8 bits = 256) * 2 bytes), I4
39 * can reference 2048 bytes ((2^9 = 512) * 4 bytes), and I8 can reference 2048
40 * bytes ((2^8 = 256) * 8 bytes). Think of it as a kind-of ring buffer for
41 * each of I2, I4, and I8 that are updated for each byte written to the output
42 * buffer. In this implementation, the output buffer is directly used for each
43 * index; there is no additional memory required. Note that the index is into
44 * a ring buffer, not a sliding window; for example, if there have been 260
45 * bytes written to the output buffer, an I2 index of 0 would index to byte 256
46 * in the output buffer, while an I2 index of 16 would index to byte 16 in the
47 * output buffer.
48 *
49 * There are also 3 special template codes; 0x1b for "repeat", 0x1c for
50 * "zeros", and 0x1e for "end". The "repeat" operation is followed by a 6 bit
51 * arg N indicating how many times to repeat. The last 8 bytes written to the
52 * output buffer are written again to the output buffer, N + 1 times. The
53 * "zeros" operation, which has no arg bits, writes 8 zeros to the output
54 * buffer. The "end" operation, which also has no arg bits, signals the end
55 * of the compressed data. There may be some number of padding (don't care,
56 * but usually 0) bits after the "end" operation bits, to fill the buffer
57 * length to a specific byte multiple (usually a multiple of 8, 16, or 32
58 * bytes).
59 *
60 * This software implementation also uses one of the undefined template values,
61 * 0x1d as a special "short data" template code, to represent less than 8 bytes
62 * of uncompressed data. It is followed by a 3 bit arg N indicating how many
63 * data bytes will follow, and then N bytes of data, which should be copied to
64 * the output buffer. This allows the software 842 compressor to accept input
65 * buffers that are not an exact multiple of 8 bytes long. However, those
66 * compressed buffers containing this sw-only template will be rejected by
67 * the 842 hardware decompressor, and must be decompressed with this software
68 * library. The 842 software compression module includes a parameter to
69 * disable using this sw-only "short data" template, and instead simply
70 * reject any input buffer that is not a multiple of 8 bytes long.
71 *
72 * After all actions for each operation code are processed, another template
73 * code is in the next 5 bits. The decompression ends once the "end" template
74 * code is detected.
75 */
76
77#include <linux/module.h>
78#include <linux/kernel.h>
79#include <linux/bitops.h>
80#include <linux/crc32.h>
81#include <asm/unaligned.h>
82
83#include <linux/sw842.h>
84
85/* special templates */
86#define OP_REPEAT (0x1B)
87#define OP_ZEROS (0x1C)
88#define OP_END (0x1E)
89
90/* sw only template - this is not in the hw design; it's used only by this
91 * software compressor and decompressor, to allow input buffers that aren't
92 * a multiple of 8.
93 */
94#define OP_SHORT_DATA (0x1D)
95
96/* additional bits of each op param */
97#define OP_BITS (5)
98#define REPEAT_BITS (6)
99#define SHORT_DATA_BITS (3)
100#define I2_BITS (8)
101#define I4_BITS (9)
102#define I8_BITS (8)
103#define CRC_BITS (32)
104
105#define REPEAT_BITS_MAX (0x3f)
106#define SHORT_DATA_BITS_MAX (0x7)
107
108/* Arbitrary values used to indicate action */
109#define OP_ACTION (0x70)
110#define OP_ACTION_INDEX (0x10)
111#define OP_ACTION_DATA (0x20)
112#define OP_ACTION_NOOP (0x40)
113#define OP_AMOUNT (0x0f)
114#define OP_AMOUNT_0 (0x00)
115#define OP_AMOUNT_2 (0x02)
116#define OP_AMOUNT_4 (0x04)
117#define OP_AMOUNT_8 (0x08)
118
119#define D2 (OP_ACTION_DATA | OP_AMOUNT_2)
120#define D4 (OP_ACTION_DATA | OP_AMOUNT_4)
121#define D8 (OP_ACTION_DATA | OP_AMOUNT_8)
122#define I2 (OP_ACTION_INDEX | OP_AMOUNT_2)
123#define I4 (OP_ACTION_INDEX | OP_AMOUNT_4)
124#define I8 (OP_ACTION_INDEX | OP_AMOUNT_8)
125#define N0 (OP_ACTION_NOOP | OP_AMOUNT_0)
126
127/* the max of the regular templates - not including the special templates */
128#define OPS_MAX (0x1a)
129
130#endif
131

source code of linux/lib/842/842.h