x86 prefixes and escape opcodes flowchart

5 comments

• st_goliath 23 minutes ago
  Fun little tidbit: The 0x40-0x4f range used for the REX prefix actually clashes with the single-byte encodings for increment/decrement.

  When AMD designed the 64 bit extension, they had run out of available single-byte opcodes to use as a prefix and decided to re-use those. The INC/DEC instructions are still available in 64 bit mode, but not in their single-byte encodings.
• debugnik 3 hours ago
  This site redirects to HN when it notices HN in the referrer.
  [-]
  • st_goliath 1 hour ago
    If you have JavaScript enabled, that is. JWZ at least does the redirect on the server side.

    The following is pulled in from `https://soc.me/assets/js/turnBack.js`:

        const undesirables = [
          "news.ycombinator.com/",
          // "reddit.com/", // disable temporaily
          "lobste.rs/"
        ] ;
    
        if (undesirables.find(site => document.referrer.includes(site))) {
          window.location.replace(document.referrer);
        }
    

    I wonder why Reddit is "temporarily not undesirable".
  • therein 1 hour ago
    Wow, I didn't even notice because I have extensions that strip the referrer header. Excellent.
  • chimpontherun 2 hours ago
    open in new tab
• dagenix 3 hours ago
  https://archive.ph/ZMsnQ
• snvzz 1 hour ago
  This is in no small part why x86 code density is awful despite variable size encoding.
  [-]
  • themafia 1 hour ago
    Awful compared to what?

    I've seen benchmarks that go both ways in terms of a "winner" but in terms of overall variance there seems to be very little. There are some cases where ARM64 or RISCV do better and there are some cases where x86_64 does better. I can't see code density being a relevant factor when picking one ISA over another.

    We've got good compilers now anyways.. outside of power consumption.. the ISA wars are dead.

    [-]
• tucnak 1 hour ago
  I respect the disobedience.