Mirror of forum.nim-lang.org

4472 :: bitsize in object? weird operation

• MarcL (orginal) [2018-12-13T23:05:17+01:00] view original

  Hi,

  I need to replicate the idea of C bitfields.

  struct iphdr {
          
          __u8	ihl:4,
                  version:4;
  }
  Run

  but in Nim, the closest I got is:

  IP_packet = object
          
          version{.bitsize:4.}:uint8
          ihl{.bitsize:4.}:uint8
  Run

  But it compiles to usual uint8 bytes (two uint8 in that case, when I should have 4 bits for each into one uint8) So, how should I do it?

  Thanks,

---

• mashingan (orginal) [2018-12-14T05:19:41+01:00] view original

  I haven't used it but perhaps this help? https://nim-lang.org/docs/manual.html#foreign-function-interface-packed-pragma

---

• MarcL (orginal) [2018-12-14T06:19:09+01:00] view original

  Thanks you,

  For some reason, it now works as expected, even without the packed pragma (which I will use anyway). The code produced is the correct one. The only difference on my systems (osx and linux) is that I changed from "brew install nim" or "apt install nim" to choosenim for both.

  Maybe..

  Anyway, thanks mashingan,

---