Function get_univ

crates/ixon/src/univ.rs:102–160

Deserialize a universe from bytes (iterative to avoid stack overflow).

(buf: &mut &[u8])

/// Deserialize a universe from bytes (iterative to avoid stack overflow).
pub fn get_univ(buf: &mut &[u8]) -> Result<Arc<Univ>, String> {
  let mut work: Vec<GetUnivFrame> = vec![GetUnivFrame::Parse];
  let mut results: Vec<Arc<Univ>> = Vec::new();

  while let Some(frame) = work.pop() {
    match frame {
      GetUnivFrame::Parse => {
        let tag = Tag2::get(buf)?;
        match tag.flag {
          Univ::FLAG_ZERO_SUCC => {
            if tag.size == 0 {
              results.push(Univ::zero());
            } else {
              // Parse inner, then wrap in Succs
              work.push(GetUnivFrame::WrapSuccs(tag.size));
              work.push(GetUnivFrame::Parse);
            }
          },
          Univ::FLAG_MAX => {
            // Parse a, parse b, then build Max(a, b)
            work.push(GetUnivFrame::BuildMax);
            work.push(GetUnivFrame::Parse); // b
            work.push(GetUnivFrame::Parse); // a
          },
          Univ::FLAG_IMAX => {
            // Parse a, parse b, then build IMax(a, b)
            work.push(GetUnivFrame::BuildIMax);
            work.push(GetUnivFrame::Parse); // b
            work.push(GetUnivFrame::Parse); // a
          },
          Univ::FLAG_VAR => {
            results.push(Univ::var(tag.size));
          },
          f => return Err(format!("get_univ: invalid flag {f}")),
        }
      },
      GetUnivFrame::WrapSuccs(count) => {
        let mut result =
          results.pop().ok_or("get_univ: missing result for WrapSuccs")?;
        for _ in 0..count {
          result = Univ::succ(result);
        }
        results.push(result);
      },
      GetUnivFrame::BuildMax => {
        let b = results.pop().ok_or("get_univ: missing b for Max")?;
        let a = results.pop().ok_or("get_univ: missing a for Max")?;
        results.push(Univ::max(a, b));
      },
      GetUnivFrame::BuildIMax => {
        let b = results.pop().ok_or("get_univ: missing b for IMax")?;
        let a = results.pop().ok_or("get_univ: missing a for IMax")?;
        results.push(Univ::imax(a, b));
      },
    }
  }

  results.pop().ok_or_else(|| "get_univ: no result".to_string())