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tehjh's profile
Jann Horn
Jann Horn
Jann Horn
@tehjh

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Jann Horn

@tehjh

works at Google Project Zero. personal account.

Joined August 2011

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    Jann Horn‏ @tehjh 7 Apr 2018
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    why do PDF readers need multiple seconds to search through something like a thousand pages of formatted text when grep can dig through the equivalent plaintext in ~50ms? is extracting plaintext from PDF that costly?

    7:43 AM - 7 Apr 2018
    • 5 Retweets
    • 34 Likes
    • limaunion Matthew Fernandez Michał Kowalczyk Bradford Larsen Christoph Siedentop David Wong Yannayl Ben Gras Arun Magesh
    8 replies 5 retweets 34 likes
      1. New conversation
      2. Jann Horn‏ @tehjh 7 Apr 2018
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        for evince, which uses libpoppler for text search in PDF, callgrind estimates 47% of time spent in pow(), called from cmsBuildSegmentedToneCurve() (56% in/below this function), which is some function for drawing curves? and further up in the call chain, there's Page::display()

        2 replies 1 retweet 5 likes
        Show this thread
      3. Jann Horn‏ @tehjh 7 Apr 2018
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        so looks like it fully layouts every page it's searching through?

        3 replies 1 retweet 3 likes
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      4. Jann Horn‏ @tehjh 7 Apr 2018
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        callgraph at https://var.thejh.net/0c7a475ebb7b7d505142d177388a9d58_evince_callgraph.png …

        1 reply 0 retweets 1 like
        Show this thread
      5. End of conversation
      1. New conversation
      2. hanno‏ @hanno 7 Apr 2018
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        Replying to @tehjh

        is it faster if you do pdftotext [file] | grep [pattern] on the commandline?

        1 reply 0 retweets 0 likes
      3. Jann Horn‏ @tehjh 7 Apr 2018
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        Replying to @hanno

        somewhat - 20s for searching through the SDM in evince, 8s for pdftotext

        0 replies 0 retweets 1 like
      4. End of conversation
      1. New conversation
      2. tj hiding under a table‏ @adventureloop 7 Apr 2018
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        Replying to @tehjh

        Searching in intel data sheets grinds my laptop to a halt. It is only 2000 pages, what year is it?

        1 reply 3 retweets 8 likes
      3. Ahmad‏ @_sudoreality 7 Apr 2018
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        Replying to @adventureloop @tehjh

        Mupdf or Zathura

        1 reply 0 retweets 1 like
      4. 1 more reply
      1. Stay Home‏ @toasted_flakes 7 Apr 2018
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        Replying to @tehjh

        I think the costly part is establishing if two pieces of text follow each other

        0 replies 1 retweet 3 likes
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      1. Aaron Grattafiori‏ @dyn___ 7 Apr 2018
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        Replying to @tehjh

        You've looked at the format right.... I mean it's a mess. Crazy table of contents pointing to various encoded chunks...etc

        0 replies 0 retweets 2 likes
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      1. Marcus Brinkmann‏ @lambdafu 7 Apr 2018
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        Replying to @tehjh

        Worst case requires that every word is stiched together from individual letters based on glyph position, guessing spaces by horizontal distance and lines by vertical location.

        0 replies 0 retweets 2 likes
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