Move library crates under 'lib/'.

Give these crates each a more standard directory layout with sources in
a 'src' sub-sirectory and Cargo.toml in the top lib/foo directory.

Add license and description fields to each.

The build script for the cretonne crate now lives in
'lib/cretonne/build.rs' separating it from the normal library sources
under 'lib/cretonne/src'.

lib/cretonne/src/constant_hash.rs

@@ -0,0 +1,74 @@
+//! Runtime support for precomputed constant hash tables.
+//!
+//! The `meta/constant_hash.py` Python module can generate constant hash tables using open
+//! addressing and quadratic probing. The hash tables are arrays that are guaranteed to:
+//!
+//! - Have a power-of-two size.
+//! - Contain at least one empty slot.
+//!
+//! This module provides runtime support for lookups in these tables.
+
+/// Trait that must be implemented by the entries in a constant hash table.
+pub trait Table<K: Copy + Eq> {
+    /// Get the number of entries in this table which must be a power of two.
+    fn len(&self) -> usize;
+
+    /// Get the key corresponding to the entry at `idx`, or `None` if the entry is empty.
+    /// The `idx` must be in range.
+    fn key(&self, idx: usize) -> Option<K>;
+}
+
+
+/// Look for `key` in `table`.
+///
+/// The provided `hash` value must have been computed from `key` using the same hash function that
+/// was used to construct the table.
+///
+/// Returns the table index containing the found entry, or `None` if no entry could be found.
+pub fn probe<K: Copy + Eq, T: Table<K> + ?Sized>(table: &T, key: K, hash: usize) -> Option<usize> {
+    debug_assert!(table.len().is_power_of_two());
+    let mask = table.len() - 1;
+
+    let mut idx = hash;
+    let mut step = 0;
+
+    loop {
+        idx &= mask;
+
+        match table.key(idx) {
+            None => return None,
+            Some(k) if k == key => return Some(idx),
+            _ => {}
+        }
+
+        // Quadratic probing.
+        step += 1;
+        // When `table.len()` is a power of two, it can be proven that `idx` will visit all
+        // entries. This means that this loop will always terminate if the hash table has even
+        // one unused entry.
+        debug_assert!(step < table.len());
+        idx += step;
+    }
+}
+
+/// A primitive hash function for matching opcodes.
+/// Must match `meta/constant_hash.py`.
+pub fn simple_hash(s: &str) -> usize {
+    let mut h: u32 = 5381;
+    for c in s.chars() {
+        h = (h ^ c as u32).wrapping_add(h.rotate_right(6));
+    }
+    h as usize
+}
+
+#[cfg(test)]
+mod tests {
+    use super::simple_hash;
+
+    #[test]
+    fn basic() {
+        // c.f. meta/constant_hash.py tests.
+        assert_eq!(simple_hash("Hello"), 0x2fa70c01);
+        assert_eq!(simple_hash("world"), 0x5b0c31d5);
+    }
+}