130 lines
5.8 KiB
C
130 lines
5.8 KiB
C
|
|
#ifndef __842_H__
|
|
#define __842_H__
|
|
|
|
/* The 842 compressed format is made up of multiple blocks, each of
|
|
* which have the format:
|
|
*
|
|
* <template>[arg1][arg2][arg3][arg4]
|
|
*
|
|
* where there are between 0 and 4 template args, depending on the specific
|
|
* template operation. For normal operations, each arg is either a specific
|
|
* number of data bytes to add to the output buffer, or an index pointing
|
|
* to a previously-written number of data bytes to copy to the output buffer.
|
|
*
|
|
* The template code is a 5-bit value. This code indicates what to do with
|
|
* the following data. Template codes from 0 to 0x19 should use the template
|
|
* table, the static "decomp_ops" table used in decompress. For each template
|
|
* (table row), there are between 1 and 4 actions; each action corresponds to
|
|
* an arg following the template code bits. Each action is either a "data"
|
|
* type action, or a "index" type action, and each action results in 2, 4, or 8
|
|
* bytes being written to the output buffer. Each template (i.e. all actions
|
|
* in the table row) will add up to 8 bytes being written to the output buffer.
|
|
* Any row with less than 4 actions is padded with noop actions, indicated by
|
|
* N0 (for which there is no corresponding arg in the compressed data buffer).
|
|
*
|
|
* "Data" actions, indicated in the table by D2, D4, and D8, mean that the
|
|
* corresponding arg is 2, 4, or 8 bytes, respectively, in the compressed data
|
|
* buffer should be copied directly to the output buffer.
|
|
*
|
|
* "Index" actions, indicated in the table by I2, I4, and I8, mean the
|
|
* corresponding arg is an index parameter that points to, respectively, a 2,
|
|
* 4, or 8 byte value already in the output buffer, that should be copied to
|
|
* the end of the output buffer. Essentially, the index points to a position
|
|
* in a ring buffer that contains the last N bytes of output buffer data.
|
|
* The number of bits for each index's arg are: 8 bits for I2, 9 bits for I4,
|
|
* and 8 bits for I8. Since each index points to a 2, 4, or 8 byte section,
|
|
* this means that I2 can reference 512 bytes ((2^8 bits = 256) * 2 bytes), I4
|
|
* can reference 2048 bytes ((2^9 = 512) * 4 bytes), and I8 can reference 2048
|
|
* bytes ((2^8 = 256) * 8 bytes). Think of it as a kind-of ring buffer for
|
|
* each of I2, I4, and I8 that are updated for each byte written to the output
|
|
* buffer. In this implementation, the output buffer is directly used for each
|
|
* index; there is no additional memory required. Note that the index is into
|
|
* a ring buffer, not a sliding window; for example, if there have been 260
|
|
* bytes written to the output buffer, an I2 index of 0 would index to byte 256
|
|
* in the output buffer, while an I2 index of 16 would index to byte 16 in the
|
|
* output buffer.
|
|
*
|
|
* There are also 3 special template codes; 0x1b for "repeat", 0x1c for
|
|
* "zeros", and 0x1e for "end". The "repeat" operation is followed by a 6 bit
|
|
* arg N indicating how many times to repeat. The last 8 bytes written to the
|
|
* output buffer are written again to the output buffer, N + 1 times. The
|
|
* "zeros" operation, which has no arg bits, writes 8 zeros to the output
|
|
* buffer. The "end" operation, which also has no arg bits, signals the end
|
|
* of the compressed data. There may be some number of padding (don't care,
|
|
* but usually 0) bits after the "end" operation bits, to fill the buffer
|
|
* length to a specific byte multiple (usually a multiple of 8, 16, or 32
|
|
* bytes).
|
|
*
|
|
* This software implementation also uses one of the undefined template values,
|
|
* 0x1d as a special "short data" template code, to represent less than 8 bytes
|
|
* of uncompressed data. It is followed by a 3 bit arg N indicating how many
|
|
* data bytes will follow, and then N bytes of data, which should be copied to
|
|
* the output buffer. This allows the software 842 compressor to accept input
|
|
* buffers that are not an exact multiple of 8 bytes long. However, those
|
|
* compressed buffers containing this sw-only template will be rejected by
|
|
* the 842 hardware decompressor, and must be decompressed with this software
|
|
* library. The 842 software compression module includes a parameter to
|
|
* disable using this sw-only "short data" template, and instead simply
|
|
* reject any input buffer that is not a multiple of 8 bytes long.
|
|
*
|
|
* After all actions for each operation code are processed, another template
|
|
* code is in the next 5 bits. The decompression ends once the "end" template
|
|
* code is detected.
|
|
*/
|
|
|
|
#include <linux/module.h>
|
|
#include <linux/kernel.h>
|
|
#include <linux/bitops.h>
|
|
#include <linux/crc32.h>
|
|
#include <asm/unaligned.h>
|
|
|
|
#include <linux/sw842.h>
|
|
|
|
/* special templates */
|
|
#define OP_REPEAT (0x1B)
|
|
#define OP_ZEROS (0x1C)
|
|
#define OP_END (0x1E)
|
|
|
|
/* sw only template - this is not in the hw design; it's used only by this
|
|
* software compressor and decompressor, to allow input buffers that aren't
|
|
* a multiple of 8.
|
|
*/
|
|
#define OP_SHORT_DATA (0x1D)
|
|
|
|
/* additional bits of each op param */
|
|
#define OP_BITS (5)
|
|
#define REPEAT_BITS (6)
|
|
#define SHORT_DATA_BITS (3)
|
|
#define I2_BITS (8)
|
|
#define I4_BITS (9)
|
|
#define I8_BITS (8)
|
|
#define CRC_BITS (32)
|
|
|
|
#define REPEAT_BITS_MAX (0x3f)
|
|
#define SHORT_DATA_BITS_MAX (0x7)
|
|
|
|
/* Arbitrary values used to indicate action */
|
|
#define OP_ACTION (0x70)
|
|
#define OP_ACTION_INDEX (0x10)
|
|
#define OP_ACTION_DATA (0x20)
|
|
#define OP_ACTION_NOOP (0x40)
|
|
#define OP_AMOUNT (0x0f)
|
|
#define OP_AMOUNT_0 (0x00)
|
|
#define OP_AMOUNT_2 (0x02)
|
|
#define OP_AMOUNT_4 (0x04)
|
|
#define OP_AMOUNT_8 (0x08)
|
|
|
|
#define D2 (OP_ACTION_DATA | OP_AMOUNT_2)
|
|
#define D4 (OP_ACTION_DATA | OP_AMOUNT_4)
|
|
#define D8 (OP_ACTION_DATA | OP_AMOUNT_8)
|
|
#define I2 (OP_ACTION_INDEX | OP_AMOUNT_2)
|
|
#define I4 (OP_ACTION_INDEX | OP_AMOUNT_4)
|
|
#define I8 (OP_ACTION_INDEX | OP_AMOUNT_8)
|
|
#define N0 (OP_ACTION_NOOP | OP_AMOUNT_0)
|
|
|
|
/* the max of the regular templates - not including the special templates */
|
|
#define OPS_MAX (0x1a)
|
|
|
|
#endif
|