TIFF LZW style - When to change the code length

[lpatiny]

Looking at the spec: https://www.fileformat.info/format/tiff/corion-lzw.htm

The function GetNextCode() retrieves the next code from the LZW-
coded data. It must keep track of bit boundaries. It knows that
the first code that it gets will be a 9-bit code. We add a table
entry each time we get a code, so GetNextCode() must switch over
to 10-bit codes as soon as string #511 is stored into the table.
We need to change the code length as soon at #511 is stored.

However in the code the change is done at 510:

tiff/src/lzw.ts

Lines 94 to 96 in 73ca971

	if (this.tableLength + 1 === 2 ** this.currentBitLength) {
	this.currentBitLength++;
	}

I don't know what is the correct version but the confusion could be due to TIFF version:

https://stackoverflow.com/questions/26366659/whats-special-about-tiff-5-0-style-lzw-compression

• LZW codes are written to the stream in reversed bit order.
• "New-style" increases the code size one symbol earlier than "old-style" (so-called "Early Change").

The current implementation in 'debug-lzw' branch seems however correct based on the lzw images we have and the comparison with convert from imagemagick.

199aa6d

[targos]

However in the code the change is done at 510:

I think it's just because #511 is if you count from one, and we count from zero.