6 ms·

Blog author here! Thanks to HN for warning me about sscanf at exactly the right time – within a day of me trying to load some ASCII STLs and noticing it was sl

Blog author here! Thanks to HN for warning me about sscanf at exactly the right time – within a day of me trying to load some ASCII STLs and noticing it was slow... Linked deep in the Twitter replies [1], there's an open glibc issue about this, dating back to 2014: https://sourceware.org/bugzilla/show_bug.cgi?id=17577 https://sourceware.org/bugzilla/show_bug.cgi?id=17577 C doesn't have any requirements on the complexity of sscanf, so it might not be a bug per se, but it's certainly... a pitfall. [1] https://twitter.com/impraxical/status/1367194430835425283 https://twitter.com/impraxical/status/1367194430835425283

rkagerer 6y ago
Hey, Matt, neat to see you here and congrats on making the front page! Recognize you from the Formlabs forums & conferences. Love that notion of professional empathy underscoring your message in the blog post.
- mkeeter 6y ago
  Hey RK! Thanks for the kind words – hopefully I'll see you again, once we're back to holding in-person events!
- koalahedron 6y ago
  I know Matt too, primarily from him rejecting my Libfive PRs for being "too 1337". But seriously, Matt, I might have a project for an in-person event regarding printing robots. Stay tuned--to what channel I don't know.
BenFrantzDale 6y ago
IMO the lack of a complexity requirement is a bug in the C standard. And really it’s a bug in the implementation(s?) too. If it can be done on O(1), shame on library authors for doing it in O(n). If you want programmers to trust library authors, don’t do this to us. Maybe std::from_chars FTW?
- ironmagma 6y ago
  Shouldn’t we just come clean and admit to ourselves that there is no such thing as the C standard? There is a collection of loosely related languages that look similar and that collectively we call C, but really they’re all completely different and share almost no interoperability or common characteristics. And those standards that do exist provide almost no ability to reason about your code including things like ordering of statements.
  - loeg 6y ago
    No, that's complete nonsense. Here's the latest revision of the standard: https://www.iso.org/standard/74528.html https://www.iso.org/standard/74528.html C has had a well-defined memory model since C11, I believe (re: "ordering of statements").
    - ironmagma 6y ago
      > ISO-C11 specifies 203 circumstances that cause undefined behaviors. 203 is enough to make almost every line of code questionable. The result of this is that looking at a simple 3 line C program and being asked whether the program terminates is undecidable without knowing which compiler was used. Null dereference for example is undefined behavior, and could cause a termination or not, depending on the implementation, even if it is known to be standards conforming to C11. [1] https://resources.tasking.com/p/undefined-behaviors-iso-c-their-effect-your-embedded-software-part-1 https://resources.tasking.com/p/undefined-behaviors-iso-c-th...
      - ncmncm 6y ago
        A good argument for compiling your debug builds with "-fsanitize=undefined".
        loeg 6y ago
        Sure, or use Rust! Rust is great! We can criticize C for its faults without making baseless claims.
Waterluvian 6y ago
I love the format of this blog post. Perfect length. Perfect detail. You don't waste words. A good number of images.
- lambda_obrien 6y ago
  And it works without javascript!
  - icemelt8 6y ago
    all blogs work without javascript.
- ignoramous 6y ago
  I like this blog post but I also happen to quite like long forms like these, too: https://mango.pdf.zone/finding-former-australian-prime-minister-tony-abbotts-passport-number-on-instagram https://mango.pdf.zone/finding-former-australian-prime-minis... / https://apenwarr.ca/log/20201227 https://apenwarr.ca/log/20201227
  - komodo009 6y ago
    The mango blog post was incredibly entertaining. Thanks for sharing.
fermienrico 6y ago
Love the post, except for the title. It is too click-baity.
echlebek 6y ago
Thanks for the great blog post, and congrats on finding that long dormant bug!
gnyman 6y ago
Thank you for introducing me to the concept/term Ascetic programming. Not sure how widely used it is, but I find it more fitting for what I try to do than minimalistic or KISS. Also, it is great to see someone write > I noticed that ASCII STL loading was really quite slow. > From startup to showing the window, it took over 1.8 seconds! I always find pleasure seeing projects which highlight just how fast modern computers really are.
- gnyman 6y ago
  Re-read my comment and to be clear, the quote and the last paragraph are not related. The last sentence was meant to refer to the Erizo project as a nice single purpose high performing tool, not as a comment to the bug that made it slow.
chromanoid 6y ago
When looking at loading performance of STLs, you may want to look at this: https://papas-best.com/stlviewer_en https://papas-best.com/stlviewer_en
froh 6y ago
printf and scanf match nicely with their format specifiers, so the serialization and deserialization can be maintained nicely in lockstep. to avoid the quadratic overheating sttlen you can simply use fmemopen(3), which makes the temporary sscanf FILE object explicit and persistent for the whole parse, and needs just one strlen call. https://news.ycombinator.com/item?id=26343149 https://news.ycombinator.com/item?id=26343149

rkagerer 6y ago

Hey, Matt, neat to see you here and congrats on making the front page! Recognize you from the Formlabs forums & conferences. Love that notion of professional empathy underscoring your message in the blog post.

mkeeter 6y ago
Hey RK! Thanks for the kind words – hopefully I'll see you again, once we're back to holding in-person events!
koalahedron 6y ago
I know Matt too, primarily from him rejecting my Libfive PRs for being "too 1337". But seriously, Matt, I might have a project for an in-person event regarding printing robots. Stay tuned--to what channel I don't know.

BenFrantzDale 6y ago

IMO the lack of a complexity requirement is a bug in the C standard. And really it’s a bug in the implementation(s?) too. If it can be done on O(1), shame on library authors for doing it in O(n). If you want programmers to trust library authors, don’t do this to us. Maybe std::from_chars FTW?

ironmagma 6y ago
Shouldn’t we just come clean and admit to ourselves that there is no such thing as the C standard? There is a collection of loosely related languages that look similar and that collectively we call C, but really they’re all completely different and share almost no interoperability or common characteristics. And those standards that do exist provide almost no ability to reason about your code including things like ordering of statements.
- loeg 6y ago
  No, that's complete nonsense. Here's the latest revision of the standard: https://www.iso.org/standard/74528.html https://www.iso.org/standard/74528.html C has had a well-defined memory model since C11, I believe (re: "ordering of statements").
  - ironmagma 6y ago
    > ISO-C11 specifies 203 circumstances that cause undefined behaviors. 203 is enough to make almost every line of code questionable. The result of this is that looking at a simple 3 line C program and being asked whether the program terminates is undecidable without knowing which compiler was used. Null dereference for example is undefined behavior, and could cause a termination or not, depending on the implementation, even if it is known to be standards conforming to C11. [1] https://resources.tasking.com/p/undefined-behaviors-iso-c-their-effect-your-embedded-software-part-1 https://resources.tasking.com/p/undefined-behaviors-iso-c-th...
    - ncmncm 6y ago
      A good argument for compiling your debug builds with "-fsanitize=undefined".
      - loeg 6y ago
        Sure, or use Rust! Rust is great! We can criticize C for its faults without making baseless claims.

Waterluvian 6y ago

I love the format of this blog post. Perfect length. Perfect detail. You don't waste words. A good number of images.

lambda_obrien 6y ago
And it works without javascript!
- icemelt8 6y ago
  all blogs work without javascript.
ignoramous 6y ago
I like this blog post but I also happen to quite like long forms like these, too: https://mango.pdf.zone/finding-former-australian-prime-minister-tony-abbotts-passport-number-on-instagram https://mango.pdf.zone/finding-former-australian-prime-minis... / https://apenwarr.ca/log/20201227 https://apenwarr.ca/log/20201227
- komodo009 6y ago
  The mango blog post was incredibly entertaining. Thanks for sharing.

fermienrico 6y ago

Love the post, except for the title. It is too click-baity.

echlebek 6y ago

Thanks for the great blog post, and congrats on finding that long dormant bug!

gnyman 6y ago

Thank you for introducing me to the concept/term Ascetic programming. Not sure how widely used it is, but I find it more fitting for what I try to do than minimalistic or KISS. Also, it is great to see someone write > I noticed that ASCII STL loading was really quite slow. > From startup to showing the window, it took over 1.8 seconds! I always find pleasure seeing projects which highlight just how fast modern computers really are.

gnyman 6y ago
Re-read my comment and to be clear, the quote and the last paragraph are not related. The last sentence was meant to refer to the Erizo project as a nice single purpose high performing tool, not as a comment to the bug that made it slow.

chromanoid 6y ago

When looking at loading performance of STLs, you may want to look at this: https://papas-best.com/stlviewer_en https://papas-best.com/stlviewer_en

froh 6y ago

printf and scanf match nicely with their format specifiers, so the serialization and deserialization can be maintained nicely in lockstep. to avoid the quadratic overheating sttlen you can simply use fmemopen(3), which makes the temporary sscanf FILE object explicit and persistent for the whole parse, and needs just one strlen call. https://news.ycombinator.com/item?id=26343149 https://news.ycombinator.com/item?id=26343149