Hey everybody welcome to the next video.
So in this video we're gonna be talking about Elsie 77 and Elsie 78.
So Elsie seventy seven the way this works is it replaces the repeated occurrences of data or characters
with a reference to a single master copy.
This master copy is normally held at the beginning of the file.
It consistently holds the amount of data and memory that it last saw when comparing matches.
So as it goes through the file to start compressing it it will keep track of the last section of data
which can be two bytes four bytes 32 bytes.
It just it just depends on how much data has to go through.
This is also known as a sliding window so the the amount of data held in memory is called the sliding
window which is gives it the name the sliding window compression.
Now on compressing this does the exact opposite forgetting forget the sliding window part but what it
does is it just goes to the file and replaces the reference with the master copy and just continuously
replaces all the references with the master copy until the data has been put back.
Now Elsie 78 while similar tells you 77 we'll look for all the repeated data like it should but it will
replace all the data with a reference like Elsie 77.
But it does it in an internal directory.
So what you'll see here is the directory and then some directory index with an index number and then
a character.
So this kind of compounds on itself pretty hard when you start looking at the single characters.
So what I'm gonna do is I'm gonna lead links above the video to Elsie 77 and Elsie 78.
So you can read a little bit more detail of exactly how it works behind the scenes.
Again on compressing this we'll just have it replace the data at the correct index or the separate or
the specific character at the correct index in the file which in turn will give it the exact output
as it had input when it compressed it.
So these again are a lossless type of compression.