+use std::convert::TryFrom;
+
+pub mod codegen;
+pub mod lexer;
+pub mod llvm;
+pub mod parser;
+
+/// Fixed size of [`SmallCStr`] including the trailing `\0` byte.
+pub const SMALL_STR_SIZE: usize = 16;
+
+/// Small C string on the stack with fixed size [`SMALL_STR_SIZE`].
+#[derive(Debug, PartialEq)]
+pub struct SmallCStr([u8; SMALL_STR_SIZE]);
+
+impl SmallCStr {
+    /// Create a new C string from `src`.
+    /// Returns [`None`] if `src` exceeds the fixed size or contains any `\0` bytes.
+    pub fn new<T: AsRef<[u8]>>(src: &T) -> Option<SmallCStr> {
+        let src = src.as_ref();
+        let len = src.len();
+
+        // Check for \0 bytes.
+        let contains_null = unsafe { !libc::memchr(src.as_ptr().cast(), 0, len).is_null() };
+
+        if contains_null || len > SMALL_STR_SIZE - 1 {
+            None
+        } else {
+            let mut dest = [0; SMALL_STR_SIZE];
+            dest[..len].copy_from_slice(src);
+            Some(SmallCStr(dest))
+        }
+    }
+
+    /// Return pointer to C string.
+    pub const fn as_ptr(&self) -> *const libc::c_char {
+        self.0.as_ptr().cast()
+    }
+}
+
+impl TryFrom<&str> for SmallCStr {
+    type Error = ();
+
+    fn try_from(value: &str) -> Result<Self, Self::Error> {
+        SmallCStr::new(&value).ok_or(())
+    }
+}
+
+/// Either type, for APIs accepting two types.
+pub enum Either<A, B> {
+    A(A),
+    B(B),
+}
+
+#[cfg(test)]
+mod test {
+    use super::{SmallCStr, SMALL_STR_SIZE};
+    use std::convert::TryInto;
+
+    #[test]
+    fn test_create() {
+        let src = "\x30\x31\x32\x33";
+        let scs = SmallCStr::new(&src).unwrap();
+        assert_eq!(&scs.0[..5], &[0x30, 0x31, 0x32, 0x33, 0x00]);
+
+        let src = b"abcd1234";
+        let scs = SmallCStr::new(&src).unwrap();
+        assert_eq!(
+            &scs.0[..9],
+            &[0x61, 0x62, 0x63, 0x64, 0x31, 0x32, 0x33, 0x34, 0x00]
+        );
+    }
+
+    #[test]
+    fn test_contain_null() {
+        let src = "\x30\x00\x32\x33";
+        let scs = SmallCStr::new(&src);
+        assert_eq!(scs, None);
+
+        let src = "\x30\x31\x32\x33\x00";
+        let scs = SmallCStr::new(&src);
+        assert_eq!(scs, None);
+    }
+
+    #[test]
+    fn test_too_large() {
+        let src = (0..SMALL_STR_SIZE).map(|_| 'a').collect::<String>();
+        let scs = SmallCStr::new(&src);
+        assert_eq!(scs, None);
+
+        let src = (0..SMALL_STR_SIZE + 10).map(|_| 'a').collect::<String>();
+        let scs = SmallCStr::new(&src);
+        assert_eq!(scs, None);
+    }
+
+    #[test]
+    fn test_try_into() {
+        let src = "\x30\x31\x32\x33";
+        let scs: Result<SmallCStr, ()> = src.try_into();
+        assert!(scs.is_ok());
+
+        let src = (0..SMALL_STR_SIZE).map(|_| 'a').collect::<String>();
+        let scs: Result<SmallCStr, ()> = src.as_str().try_into();
+        assert!(scs.is_err());
+
+        let src = (0..SMALL_STR_SIZE + 10).map(|_| 'a').collect::<String>();
+        let scs: Result<SmallCStr, ()> = src.as_str().try_into();
+        assert!(scs.is_err());
+    }
+}
+

+