blob: e0a122bc1cdb06d25c686d5e7fb68c7217169e96 [file] [log] [blame]
#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)
/* the max of the regular templates - not including the special templates */
#define OPS_MAX (0x1a)