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This commit is contained in:
Eric MacDonald
2021-09-08 22:31:02 -04:00
parent 2d6533536b
commit 848ff5df74
1 changed files with 10 additions and 0 deletions
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10
zefie_wtvp_minisrv/WTVLzpf.js
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@@ -393,12 +393,15 @@ class WTVLzpf {
this.ring_buffer[i & 0x1FFF] = byte;
if (this.match_index > 0) {
// Cozy time
if (byte != this.ring_buffer[this.ring_bufer_index] || this.match_index > 0x0127) {
// End of matching. Either we no longer match or we reached out limit.
code_length = this.matchEncode[this.match_index][1];
code = this.matchEncode[this.match_index][0];
this.match_index = 0;
this.type_index = 3;
} else {
// Previous iteration found a match so we continue matching until we can't.
this.match_index = (this.match_index + 1) & 0x1FFF;
this.ring_bufer_index = (this.ring_bufer_index + 1) & 0x1FFF;
this.checksum = (this.checksum + byte) & 0xFFFF;
@@ -409,26 +412,33 @@ class WTVLzpf {
this.ring_bufer_index = 0xFFFF;
if (i >= 3) {
// Start recoding data so we can lookup matches.
hash_index = (this.working_data >>> 0x0B ^ this.working_data) & 0x0FFF;
this.ring_bufer_index = this.hash_table[hash_index];
this.hash_table[hash_index] = i & 0x1FFF;
} else {
// The first three uncompressed bytes aren't used for the matching algorithm.
this.type_index++;
}
if (this.ring_bufer_index == 0xFFFF) {
// We never seen this byte before so we encode it with our Huffman dictionary.
code_length = this.nomatchEncode[byte][1];
code = this.nomatchEncode[byte][0] << 0x10;
} else if (byte == this.ring_buffer[this.ring_bufer_index] && compress_data) {
// Wow dude, a match has been found. Let's switch get our own room in the next iteration to see if we match further.
this.match_index = 1;
this.ring_bufer_index = (this.ring_bufer_index + 1) & 0x1FFF;
this.type_index = 4;
} 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 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 = this.nomatchEncode[byte][0] << 0x0F;
}
this.checksum = (this.checksum + byte) & 0xFFFF;
// We work on a 2-byte context so we store the last two bytes so we can do cool lookups with it
this.working_data = ((this.working_data * 0x0100) + byte) & 0xFFFFFFFF;
i++;
}