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Initial code for Lzpf stream compression

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This commit is contained in:
Eric MacDonald
2021-08-07 15:29:20 -04:00
parent 1c8e0adbaf
commit eb6fc5f89a
1 changed files with 95 additions and 47 deletions
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142
zefie_wtvp_minisrv/WTVLzpf.js
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@@ -14,6 +14,10 @@ class WTVLzpf {
current_length = 0
current_literal = 0
working_data = 0;
match_index = 0;
type_index = 0;
checksum = 0;
flag_table = new Uint16Array(0x1000)
ring_buffer = new Uint8Array(0x2000)
compressed_data = [];
@@ -277,11 +281,26 @@ class WTVLzpf {
clear() {
this.current_length = 0;
this.current_literal = 0;
this.working_data = 0;
this.match_index = 0;
this.type_index = 0;
this.checksum = 0;
this.ring_buffer.fill(0x00, 0, 0x2000)
this.flag_table.fill(0xFFFF, 0, 0x1000);
this.compressed_data = [];
}
/**
* Appends a byte to the end of the compressed byte array. Re-allocates as needed
*
* @param byte {Number} char code of the byte to be added.
*
* @returns {undefined}
*/
AddByte(byte) {
this.compressed_data.push(byte);
}
/**
* Encodes a literal onto the compressed byte array.
*
@@ -297,13 +316,72 @@ class WTVLzpf {
this.current_length += code_length;
while (this.current_length > 7) {
this.compressed_data.push((this.current_literal >>> 0x18) & 0xFF);
this.AddByte((this.current_literal >>> 0x18) & 0xFF);
this.current_length -= 8;
this.current_literal = (this.current_literal << 8) & 0xFFFFFFFF;
}
}
/**
* Starts a compression stream
*
* @returns {undefined} Lzpf compression data
*/
Begin() {
this.clear();
}
/**
* Compress a block of data. Used for streamed chunks.
*
* @param uncompressed_data {String} data to compress
*
* @returns {Buffer} Lzpf compression data
*/
CompressBlock(uncompressed_data) {
}
/**
* Ends a compression stream.
*
* @param type_index {Number} the end type used to finalize
*
* @returns {Buffer} Lzpf compression data
*/
Finalize() {
var code_length = -1
var code = -1
if (this.type_index == 2) {
this.EncodeLiteral(0x10, 0x00990000);
} else if (this.type_index >= 3) {
if (this.type_index == 4) {
code_length = this.matchEncode[this.match_index][1];
code = this.matchEncode[this.match_index][0];
this.EncodeLiteral(code_length, code);
}
var flags_index = (this.working_data >>> 0x0B ^ this.working_data) & 0x0FFF;
var flag = this.flag_table[flags_index];
if (flag == 0xFFFF) {
this.EncodeLiteral(0x10, 0x00990000);
} else {
this.EncodeLiteral(0x11, 0x004c8000);
}
}
// Below is just metadata. The compressed block is complete.
// Encode checksum
this.EncodeLiteral(0x08, (this.checksum << 0x10) & 0xFFFFFFFF);
this.EncodeLiteral(0x08, (this.checksum << 0x18) & 0xFFFFFFFF);
// End
this.AddByte((this.current_literal >>> 0x18) & 0xFF);
this.AddByte(0x20);
}
/**
* Compress data using WebTV's Lzpf compression algorithm and adds the footer to the end.
*
@@ -324,12 +402,8 @@ class WTVLzpf {
var uncompressed_len = uncompressed_data.length;
var i = 0;
var sum = 0;
var working_data = 0;
var flag = 0xFFFF;
var flags_index = 0;
var match_index = 0;
var type_index = 0;
while(i < uncompressed_len) {
var code_length = -1;
var code = -1;
@@ -337,44 +411,44 @@ class WTVLzpf {
var byte = uncompressed_data.readUInt8(i);
this.ring_buffer[i & 0x1FFF] = byte;
if(match_index > 0) {
if (byte != this.ring_buffer[flag] || match_index > 0x0127) {
code_length = this.matchEncode[match_index][1];
code = this.matchEncode[match_index][0];
match_index = 0;
type_index = 3;
if (this.match_index > 0) {
if (byte != this.ring_buffer[flag] || this.match_index > 0x0127) {
code_length = this.matchEncode[this.match_index][1];
code = this.matchEncode[this.match_index][0];
this.match_index = 0;
this.type_index = 3;
} else {
match_index = (match_index + 1) & 0x1FFF;
this.match_index = (this.match_index + 1) & 0x1FFF;
flag = (flag + 1) & 0x1FFF;
sum = (sum + byte) & 0xFFFF;
working_data = ((working_data * 0x0100) + byte) & 0xFFFFFFFF;
this.checksum = (this.checksum + byte) & 0xFFFF;
this.working_data = ((this.working_data * 0x0100) + byte) & 0xFFFFFFFF;
i++;
}
} else {
flag = 0xFFFF;
if (i >= 3) {
flags_index = (working_data >>> 0x0B ^ working_data) & 0x0FFF;
flags_index = (this.working_data >>> 0x0B ^ this.working_data) & 0x0FFF;
flag = this.flag_table[flags_index];
this.flag_table[flags_index] = i & 0x1FFF;
} else {
type_index++;
this.type_index++;
}
if (flag == 0xFFFF) {
code_length = this.nomatchEncode[byte][1];
code = this.nomatchEncode[byte][0] << 0x10;
} else if (byte == this.ring_buffer[flag]) {
match_index = 1;
this.match_index = 1;
flag = (flag + 1) & 0x1FFF;
type_index = 4;
this.type_index = 4;
} else {
code_length = this.nomatchEncode[byte][1] + 1;
code = this.nomatchEncode[byte][0] << 0x0F;
}
sum = (sum + byte) & 0xFFFF;
working_data = ((working_data * 0x0100) + byte) & 0xFFFFFFFF;
this.checksum = (this.checksum + byte) & 0xFFFF;
this.working_data = ((this.working_data * 0x0100) + byte) & 0xFFFFFFFF;
i++;
}
@@ -383,33 +457,7 @@ class WTVLzpf {
}
}
// Finish up. This would normally be in an Lzpf_Finish method.
if(type_index == 2) {
this.EncodeLiteral(0x10, 0x00990000);
} else if(type_index >= 3) {
if(type_index == 4) {
code_length = this.matchEncode[match_index][1];
code = this.matchEncode[match_index][0];
this.EncodeLiteral(code_length, code);
}
flags_index = (working_data >>> 0x0B ^ working_data) & 0x0FFF;
if (flags_index == 0xFFFF) {
this.EncodeLiteral(0x10, 0x00990000);
} else {
this.EncodeLiteral(0x11, 0x004c8000);
}
}
// Below is just metadata. The compressed block is complete.
// Encode checksum
this.EncodeLiteral(0x08, (sum << 0x10) & 0xFFFFFFFF);
this.EncodeLiteral(0x08, (sum << 0x18) & 0xFFFFFFFF);
// End
this.compressed_data.push(this.current_literal >>> 0x18);
this.compressed_data.push(0x20);
this.Finalize();
return Buffer.from(this.compressed_data);
}