lib/842/842.h

12  * template operation.  For normal operations, each arg is either a specific
14  * to a previously-written number of data bytes to copy to the output buffer.
16  * The template code is a 5-bit value.  This code indicates what to do with
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
23  * in the table row) will add up to 8 bytes being written to the output buffer.
28  * corresponding arg is 2, 4, or 8 bytes, respectively, in the compressed data
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
40  * bytes ((2^8 = 256) * 8 bytes).  Think of it as a kind-of ring buffer for
44  * a ring buffer, not a sliding window; for example, if there have been 260
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
53  * "zeros" operation, which has no arg bits, writes 8 zeros to the output
57  * length to a specific byte multiple (usually a multiple of 8, 16, or 32
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
65  * buffers that are not an exact multiple of 8 bytes long.  However, those
68  * library.  The 842 software compression module includes a parameter to
70  * reject any input buffer that is not a multiple of 8 bytes long.
92  * a multiple of 8.
100 #define I2_BITS		(8)
102 #define I8_BITS		(8)