[build] Move settings generation from Python to Rust code;

lib/codegen/meta/src/constant_hash.rs

@@ -0,0 +1,50 @@
+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
+}
+
+/// Compute an open addressed, quadratically probed hash table containing
+/// `items`. The returned table is a list containing the elements of the
+/// iterable `items` and `None` in unused slots.
+pub fn generate_table<T, H: Fn(&T) -> usize>(items: &Vec<T>, hash_function: H) -> Vec<Option<&T>> {
+    let size = (1.20 * items.len() as f64) as usize;
+    // TODO do we really need the multiply by two here?
+    let size = if size.is_power_of_two() {
+        size * 2
+    } else {
+        size.next_power_of_two()
+    };
+
+    let mut table: Vec<Option<&T>> = Vec::new();
+    table.resize(size, None);
+
+    for i in items {
+        let mut h = hash_function(i) % size;
+        let mut s = 0;
+        while table[h].is_some() {
+            s += 1;
+            h = (h + s) % size;
+        }
+        table[h] = Some(i);
+    }
+
+    table
+}
+
+#[test]
+fn test_generate_table() {
+    let v = vec!["Hello".to_string(), "world".to_string()];
+    let table = generate_table(&v, |s| simple_hash(&s));
+    assert_eq!(
+        table,
+        vec![
+            None,
+            Some(&"Hello".to_string()),
+            Some(&"world".to_string()),
+            None
+        ]
+    );
+}