fn punycode_decode Result>()

in sgx_demangle/src/v0.rs [159:244]
67 lines of code
9 McCabe index (conditional complexity)

    fn punycode_decode<F: FnMut(usize, char) -> Result<(), ()>>(
        &self,
        mut insert: F,
    ) -> Result<(), ()> {
        let mut punycode_bytes = self.punycode.bytes().peekable();
        if punycode_bytes.peek().is_none() {
            return Err(());
        }

        let mut len = 0;

        // Populate initial output from ASCII fragment.
        for c in self.ascii.chars() {
            insert(len, c)?;
            len += 1;
        }

        // Punycode parameters and initial state.
        let base = 36;
        let t_min = 1;
        let t_max = 26;
        let skew = 38;
        let mut damp = 700;
        let mut bias = 72;
        let mut i: usize = 0;
        let mut n: usize = 0x80;

        loop {
            // Read one delta value.
            let mut delta: usize = 0;
            let mut w = 1;
            let mut k: usize = 0;
            loop {
                use core::cmp::{max, min};

                k += base;
                let t = min(max(k.saturating_sub(bias), t_min), t_max);

                let d = match punycode_bytes.next() {
                    Some(d @ b'a'..=b'z') => d - b'a',
                    Some(d @ b'0'..=b'9') => 26 + (d - b'0'),
                    _ => return Err(()),
                };
                let d = d as usize;
                delta = delta.checked_add(d.checked_mul(w).ok_or(())?).ok_or(())?;
                if d < t {
                    break;
                }
                w = w.checked_mul(base - t).ok_or(())?;
            }

            // Compute the new insert position and character.
            len += 1;
            i = i.checked_add(delta).ok_or(())?;
            n = n.checked_add(i / len).ok_or(())?;
            i %= len;

            let n_u32 = n as u32;
            let c = if n_u32 as usize == n {
                char::from_u32(n_u32).ok_or(())?
            } else {
                return Err(());
            };

            // Insert the new character and increment the insert position.
            insert(i, c)?;
            i += 1;

            // If there are no more deltas, decoding is complete.
            if punycode_bytes.peek().is_none() {
                return Ok(());
            }

            // Perform bias adaptation.
            delta /= damp;
            damp = 2;

            delta += delta / len;
            let mut k = 0;
            while delta > ((base - t_min) * t_max) / 2 {
                delta /= base - t_min;
                k += base;
            }
            bias = k + ((base - t_min + 1) * delta) / (delta + skew);
        }
    }