kmod's blog

  • PoolJacking: easy 51% attacks against Bitcoin and Ethereum

    With the recent Ethereum Classic double-spend attack, I decided to finally write this post about an existing vulnerability in Bitcoin and Ethereum.  The attack vector has been used in the past to steal a small amount of Bitcoin, but it can be used more cleverly to pull off 51% attacks and double-spend an unbounded amount of […]

    Kevin Modzelewski

    January 22, 2019
    bitcoin
  • Update on NumPy acceleration

    I’ve been looking into accelerating NumPy using TensorFlow, and the results have been pretty interesting.  Here’s a quick update. tldr: TensorFlow adds a lot of overhead and doesn’t speed up CPU execution, making converting NumPy->TensorFlow less promising.  TensorFlow’s ability to target GPUs, though, makes up for the overheads, but not all NumPy programs are GPU-friendly. […]

    Kevin Modzelewski

    June 25, 2017
    Uncategorized
  • Monitor crashes

    I’ve gotten a new problem in my life: my monitor has started crashing.  To be fair, the steps that cause it are fairly esoteric (using the USB ports, then switch the video input), but the failure mode is pretty remarkable: the monitor becomes completely unresponsive.  As in, I can’t switch the video mode again.  And […]

    Kevin Modzelewski

    April 11, 2017
    Uncategorized
  • Persuasiveness and selection bias

    I happened to be watching the Oscars last night, and I was pretty shocked to see the mistake with the Best Picture award.  Thinking back on it, this is a bit surprising to me: many things are happening that should be more “shocking” (all the craziness in Washington) but don’t seem to affect me the […]

    Kevin Modzelewski

    February 27, 2017
    Uncategorized
  • Personal thoughts about Pyston’s outcome

    I try to not read HN/Reddit too much about Pyston, since while there are certainly some smart and reasonable people on there, there also seem to be quite a few people with axes to grind (*cough cough* Python 3).  But there are some recurring themes I noticed in the comments about our announcement about Pyston’s […]

    Kevin Modzelewski

    February 1, 2017
    Pyston
  • NumPy to Theano / TensorFlow: Yea or Nay?

    Hey all, I’m investigating an idea and it’s gotten to the point that I’d like to solicit feedback.  The idea is to use Theano or TensorFlow to accelerate existing NumPy programs.  The technical challenges here are pretty daunting, but I feel like I have a decent understanding of its feasibility (I have a prototype that […]

    Kevin Modzelewski

    January 17, 2017
    Uncategorized
  • Amazon-Walmart arbitrage

    I recently ordered some junk food from Amazon, despite my wife’s objections. I ordered it from an Amazon Market (aka third party) seller since that was the choice picked by Amazon for one-click ordering. The food arrived, and the interesting thing is that it arrived in a Walmart box, with a Walmart packing slip. Evidently, […]

    Kevin Modzelewski

    January 15, 2017
    Uncategorized
  • What does this print, #2

    I meant to post more of these, but here’s one for fun: class A(object): def __eq__(self, rhs): return True class B(object): def __eq__(self, rhs): return False print A() in [B()] print B() in [A()] Maybe not quite as surprising once you see the results and think about it, but getting this wrong was the source […]

    Kevin Modzelewski

    October 3, 2016
    Uncategorized
  • Stack vs Register bytecodes for Python

    There seems to be a consensus that register bytecodes are superior to stack bytecodes.  I don’t quite know how to cite “common knowledge”, but doing a google search for “Python register VM” or “stack vs register vm” supports the fact that many people believe this.  There was a comment on this blog to this effect as well. […]

    Kevin Modzelewski

    July 28, 2016
    Uncategorized
  • Why is Python slow

    In case you missed it, Marius recently wrote a post on the Pyston blog about our baseline JIT tier.  Our baseline JIT sits between our interpreter tier and our LLVM JIT tier, providing better speed than the interpreter tier but lower startup overhead than the LLVM tier. There’s been some discussion over on Hacker News, and the discussion […]

    Kevin Modzelewski

    July 2, 2016
    Pyston
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