Format adsb code

adsb/src/hex.rs

@@ -0,0 +1,44 @@
+use crate::error::Error;
+
+pub fn hex_to_bytes(s: &str) -> crate::error::Result<Vec<u8>> {
+  let bytes = s.as_bytes();
+  if bytes.len() % 2 != 0 {
+    return Err(Error::new(format!(
+      "hex string must have even length, got {}",
+      bytes.len()
+    )));
+  }
+
+  let mut out = Vec::with_capacity(bytes.len() / 2);
+  for chunk in bytes.chunks(2) {
+    let hi = match hex_val(chunk[0]) {
+      Some(hi) => hi,
+      None => {
+        return Err(Error::new(format!(
+          "invalid hex char '{}'",
+          chunk[0] as char
+        )));
+      }
+    };
+    let lo = match hex_val(chunk[1]) {
+      Some(lo) => lo,
+      None => {
+        return Err(Error::new(format!(
+          "invalid hex char '{}'",
+          chunk[1] as char
+        )));
+      }
+    };
+    out.push((hi << 4) | lo);
+  }
+  Ok(out)
+}
+
+fn hex_val(b: u8) -> Option<u8> {
+  match b {
+    b'0'..=b'9' => Some(b - b'0'),
+    b'a'..=b'f' => Some(b - b'a' + 10),
+    b'A'..=b'F' => Some(b - b'A' + 10),
+    _ => None,
+  }
+}