Re^2: Data compression by 50% + : is it possible?

Hello Roboticus,

I just realized that we had the same ideas (me just later ;).

One difference is that you want to encode each of the 9 groups individually with 6 bits each => 6*9=54 bits per line while I'm encoding a whole line as a polynom

Sum($g($i) * 50**$i) with $i=0 .. 8

resulting in the need of 51 bits per line.

But I don't understand why you say

> That's not quite enough to crunch out half the space

The old encoding needs per line in average >14 bytes plus newline.

That's > 15 * 8 = 120 bits

So your 54 bits need already less than half the space!

What am I missing?

Cheers Rolf
_{(addicted to the Perl Programming Language :)

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Re^3: Data compression by 50% + : is it possible? by roboticus (Chancellor) on May 12, 2019 at 12:09 UTC
LanX: You're not missing anything that I know of. What I was basing my "not quite" phrasing on is the idea of using a single character to encode each group (@c) into a character, so it would use 9 characters (72) bits. Had I thought of just packing the required 51 bit records together, it would be more than sufficient to get 50% compression, as the file would take 635 bytes to encode 100 records (sans newlines). (The 51 bits came from: 50 different possibilities for each group of 10 in the inner loop (log2(50) == 5.64.. bits/group) * (9 groups) == 50.79 bits.) ...roboticus When your only tool is a hammer, all problems look like your thumb.	[reply]
Re^4: Data compression by 50% + : is it possible? by LanX (Saint) on May 12, 2019 at 12:32 UTC
> using a single character to encode each group (@c) into a character, so it would use 9 characters (72) bits Oh I see, but I hope you are aware that your approach can easily be packed into 9*6=54 bits and is easier to code than mine. With a per line ratio of 7 bytes = 56 bits you'll already have a 50%+ compression. My approach would require modulo 50 calculations on 51 bit integers, not sure how tricky this is on a 32 bit machine. So I'd rather "waste" 5 bits/line for a pragmatic solution. Btw: I'm reluctant trying to implement Huffman here, because the OP could probably change the parameters in his next post. Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}	[reply]


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