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This commit is contained in:
Eric MacDonald
2021-09-10 23:26:10 -04:00
parent f2c2f8f03d
commit eed5782d88
1 changed files with 7 additions and 7 deletions
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14
zefie_wtvp_minisrv/WTVLzpf.js
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@@ -40,11 +40,11 @@ class WTVLzpf {
* - Bytes that don't change the length of the bit stream: 024:MW_kvy * - Bytes that don't change the length of the bit stream: 024:MW_kvy
* - The rest will increase the length of bit stream * - The rest will increase the length of bit stream
* *
* I don't know what process they used to build this dictionary. I assume they * I don't know what process they used to build this table. I assume they
* frequency-scanned a bunch of HTML files they had. * frequency-scanned a bunch of HTML files they had.
* *
* Using ISO-8859-1 chracter encoding. Didn't seem like they used a different * Using ISO-8859-1 chracter encoding. Didn't seem like they used a different
* dictionary for Japan builds (ISO-2022-JP). * table for Japan builds (ISO-2022-JP).
**/ **/
nomatchEncode = [ nomatchEncode = [
/* [FLATTENED HUFFMAN CODE, CODE BIT LENGTH] */ /* [FLATTENED HUFFMAN CODE, CODE BIT LENGTH] */
@@ -138,13 +138,13 @@ class WTVLzpf {
/** /**
* This is the dictionary that reduces the size based on repeated patterns in the file. * This is the table that reduces the size based on repeated patterns in the file.
* *
* When we find a byte match in the ring buffer we use this dictionary to encode the length of the matched bytes. * When we find a byte match in the ring buffer we use this table to encode the length of the matched bytes.
* *
* - These are intentionally 32-bit. The leftmost flag bit is 1 in each of these to tell the decoder to use match decoding. * - These are intentionally 32-bit. The leftmost flag bit is 1 in each of these to tell the decoder to use match decoding.
* - LZP hash bits are used to encode the position where the matched bytes start. * - LZP hash bits are used to encode the position where the matched bytes start.
* - We're allowed to match up to 298 bytes before we can't encode more (we need an entry in this dictionary for each byte more). * - We're allowed to match up to 298 bytes before we can't encode more (we need an entry in this table for each byte more).
* - We can reach for matches 65KB behind the current LZ cursor (65KB is the ring buffer size and highest a 16-bit hash can reach). * - We can reach for matches 65KB behind the current LZ cursor (65KB is the ring buffer size and highest a 16-bit hash can reach).
**/ **/
matchEncode = [ matchEncode = [
@@ -422,7 +422,7 @@ class WTVLzpf {
} }
if (this.ring_bufer_index == 0xFFFF) { if (this.ring_bufer_index == 0xFFFF) {
// We never seen this byte before so we encode it with our Huffman dictionary. // We never seen this byte before so we encode it with our Huffman table.
code_length = this.nomatchEncode[byte][1]; code_length = this.nomatchEncode[byte][1];
code = this.nomatchEncode[byte][0] << 0x10; code = this.nomatchEncode[byte][0] << 0x10;
} else if (byte == this.ring_buffer[this.ring_bufer_index] && compress_data) { } else if (byte == this.ring_buffer[this.ring_bufer_index] && compress_data) {
@@ -431,7 +431,7 @@ class WTVLzpf {
this.ring_bufer_index = (this.ring_bufer_index + 1) & 0x1FFF; this.ring_bufer_index = (this.ring_bufer_index + 1) & 0x1FFF;
this.compression_mode = 4; this.compression_mode = 4;
} else { } else {
// We've seen these bytes before but the index in the ring buffer doesn't match so we revert to our neat Huffman dictionary // We've seen these bytes before but the index in the ring buffer doesn't match so we revert to our neat Huffman table
// We add 1 flag bit of 0 to account for the fact we've had a hash table hit but no hit in the ring buffer. // We add 1 flag bit of 0 to account for the fact we've had a hash table hit but no hit in the ring buffer.
code_length = this.nomatchEncode[byte][1] + 1; code_length = this.nomatchEncode[byte][1] + 1;
code = this.nomatchEncode[byte][0] << 0x0F; code = this.nomatchEncode[byte][0] << 0x0F;