Iburinoc

Joined 12 years ago

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Jan 25

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Addition/subtraction are also much simpler/cheaper than they would be in an entirely logarithmic model. If floats were just 2^x with some 64 bit fixed point x, it's not clear to me how to do addition efficiently.

Comment · 7 years ago

The "200 basis point spread" comes from the difference between the very low or non-existent interest paid on the cash in brokerage accounts and the rates the brokerage can earn by lending that money out basically risk-free. If you keep 10% of your assets in cash, a 200 bp interest spread becomes effectively a 20 bp management fee on your assets.

Comment · 7 years ago

The problem being solved essentially is: you have two binary strings, and you want to offset one of them so that they match up the best. For each offset, you're taking a dot product of one sequence with the offset version of the other. This is the same as computing the convolution of the two sequences together (https://en.wikipedia.org/wiki/Convolution). Computing this naively would be O(n^2) (doing linear work for each possible offset).

One property of the Fourier transform is that convolution in the time domain corresponds to element-wise multiplication in the frequency domain (https://en.wikipedia.org/wiki/Convolution_theorem), so you can compute the convolution efficiently by taking the FFT of both series, doing element-wise multiplication, and then taking the inverse FFT of the result.

Comment · 9 years ago

In general, xz beats zstd in compression ratio, as xz is very committed to providing the strongest compression, at the expense of speed, while zstd provides a range of compression ratio vs speed tradeoffs [0]. At the lower levels, zstd isn't approaching xz's compression level, but it's doing it much much faster. Additionally, zstd generally massively outperforms xz in decompression speed

  $ time xz linux-4.14-rc6.tar

  real    4m26.009s
  user    4m24.828s
  sys     0m0.724s

  $ wc -c linux-4.14-rc6.tar.xz
  103705148 linux-4.14-rc6.tar.xz

  $ time zstd --ultra -20 linux-4.14-rc6.tar
  linux-4.14-rc6.tar   : 12.81%   (824350720 => 105564246 bytes, linux-4.14-rc6.tar.zst)

  real    4m34.129s
  user    4m33.484s
  sys     0m0.432s

  $ time cat linux-4.14-rc6.tar.xz | xz -d > out1                                                                                                                                           

  real    0m9.677s
  user    0m6.608s
  sys     0m0.704s

  $ time cat linux-4.14-rc6.tar.zst | zstd -d > out2

  real    0m1.702s
  user    0m1.220s
  sys     0m0.520s

[0]: https://github.com/facebook/zstd/blob/dev/doc/images/DCspeed...

Comment · 9 years ago

Well sure, but from an asymptotic approach both unsorted and sorted are "linear", so asymptotics don't necessarily provide enough information to answer GP's question.

Comment · 10 years ago

The article mentions the applicable exception:

> Everyone who is born in Canada is eligible for Canadian citizenship, with one exception: those who are born to employees of foreign governments.

Comment · 10 years ago

I'm not sure where you are but I find it quite uncommon for university students.

Comment · 10 years ago

I'm not sure about the US but in Canada it's certainly not true that everyone has data plans (in fact as far as I can tell unless you have a company sponsored phone, data plans are in the minority), and SMS remains a cheap communication method that is more or less guaranteed to work.

Comment · 12 years ago

If you actually think that and aren't just trolling, would you care to back up your statements?

While the Ontario debt is larger than the California debt, it's not really a fair comparison.[1][2]

And on the communist state bit, uh what?

[1]: http://www.thestar.com/opinion/commentary/2014/03/21/ontario... [2]: http://blogs.wsj.com/canadarealtime/2014/03/18/ontario-debt-...

Comment · 12 years ago

Perhaps I misunderstand you but since it's HTTPS, in theory there are no MITM attacks.

Comment · 12 years ago

This looks cool really cool! I like the site, however it can be hard to read the text with the flashy background. Perhaps have the flashy background scroll up with the first "panel"?

On the crypto side of things, are there any plans to create native clients? While I don't doubt that you guys are trustworthy, it would be nice if I didn't have to trust that the javascript I was being served didn't change between visits.

All in all it looks good, albeit with some trust issues...

Comment · 12 years ago

While that is true, part of the contents that is hashed is the time of commit. Therefore if you (somehow...) managed to get that hash, you could just reset and commit again. Or amend.

In any case, I believe he was joking. The odds of a sha1 collision are very very low.

Comment · 12 years ago

Ok, thanks for the reply. Do you guys have any plans to try client-side encryption at some point in the future and/or do file encryption as well? I have to agree with kenrikm to some degree, if the encryption and decryption is all done server side then we are really just trusting you not to cheat (Not saying you're untrustworthy, but it does seem to be a service built on security, which is a field in which I'd rather trust as few people as possible).

Comment · 12 years ago

Looks interesting, although more information on the encryption schemes used, how the key is stored/represented/generated would be nice given that the idea is to trust the service with my private data.