5 ms·

All I did was take your for-loop code and translated into idiomatic Go code. My point is the for-loop in Go isn't as terrible as the loop example you wrote.

• pcwalton 12y ago
  Your version infinite loops: http://play.golang.org/p/uglbTETE6d http://play.golang.org/p/uglbTETE6d See why for loops are tricky? :)
  • jaekwon 12y ago
    Doh! I fell straight in :) Overflows in general are tricky. How does Rust deal with it?
    • pcwalton 12y ago
      We have special checked types you can use if you want checked arithmetic. The default is to not check, because CPUs currently make it expensive to check (although I would love it if that could change--we need hardware support though).
      • jaekwon 12y ago
        Nice. :)
      • acqq 12y ago
        But CPU's have the overflow flag, that is actually set if the operation overflows? You can't write that check explicitly in C, but you can in assembler. Available now, across the different hardware.
        • dbaupp 12y ago
          As you say, detecting the overflow is easy, but efficiently handling it is not. It adds a branch to every single arithmetic operation, and it makes it much harder for the compiler to optimise things e.g. it is hard to vectorise a loop summing an array, if every + has a conditional branch on the overflow flag. (Also, I believe it introduces a lot of data dependencies, getting in the way of the out-of-order execution of modern CPUs.)
          • acqq 12y ago
            To handle the overflow on the places where you want to handle them, modern processor doesn't have any problem with an additional jump instruction. Also, modern compilers could optimize the checks away if they aren't used. In effect, implementing overflow checks definitely won't turn your C speed (1s) code in a Python speed (40s) code. I estimate it wouldn't be even two times slower in most of the use cases. It's certainly not the problem of the CPU's. It can be the problem of the certain compilers if they don't have the infrastructure to reason about overflow flags though. But it's not a hardware problem.
            • masklinn 12y ago
              > I estimate it wouldn't be even two times slower in most of the use cases. In his "We Need Hardware Traps for Integer Overflow"[0], Regher quotes 5% to 100% overhead for languages such as JS or Racket, and that a "highly tuned" checker would likely be in the 5% range. Playing with arithmetics-heavy programs and Rust's checked_* (which are backed by LLVM's overflow intrinsics[1]) I got anywhere from 5 to 40% performance loss IIRC. That's not a lot, but at the same time when you're competing with languages specifically not paying those 5%, a 5% hit on all computations is not going to get you much love. Which is why Rust currently lets you do that (via num::Checked* and num::Saturating) but uses overflowing default semantics. [0] http://blog.regehr.org/archives/1154 http://blog.regehr.org/archives/1154 [1] http://llvm.org/docs/LangRef.html#arithmetic-with-overflow-intrinsics http://llvm.org/docs/LangRef.html#arithmetic-with-overflow-i...
              • masklinn 12y ago
                OTOH I must note that Swift, on the other hand, has opted to error on overflow and have a second set of overflowing operators: https://developer.apple.com/library/mac/documentation/swift/conceptual/swift_programming_language/AdvancedOperators.html#//apple_ref/doc/uid/TP40014097-CH27-XID_73 https://developer.apple.com/library/mac/documentation/swift/...
                • acqq 12y ago
    • deleted 12y ago
      [deleted]
  • codygman 12y ago
    I love when arguments are decided by/proven by runnable code examples.
  • hit8run 12y ago
    Just use int and it works fine: http://play.golang.org/p/nZcd3M5aL_ http://play.golang.org/p/nZcd3M5aL_ To me golang is readable while even small rust examples don't feel quite right right.
    • masklinn 12y ago
      > Just use int and it is a completely different piece of code.