Rename the 'cretonne' crate to 'cretonne-codegen'.

This fixes the next part of #287.

lib/codegen/meta/constant_hash.py

@@ -0,0 +1,63 @@
+"""
+Generate constant hash tables.
+
+The `constant_hash` module can generate constant pre-populated hash tables. We
+don't attempt parfect hashing, but simply generate an open addressed
+quadratically probed hash table.
+"""
+from __future__ import absolute_import
+from cdsl import next_power_of_two
+
+try:
+    from typing import Any, List, Iterable, Callable  # noqa
+except ImportError:
+    pass
+
+
+def simple_hash(s):
+    # type: (str) -> int
+    """
+    Compute a primitive hash of a string.
+
+    Example:
+        >>> "0x%x" % simple_hash("Hello")
+        '0x2fa70c01'
+        >>> "0x%x" % simple_hash("world")
+        '0x5b0c31d5'
+    """
+    h = 5381
+    for c in s:
+        h = ((h ^ ord(c)) + ((h >> 6) + (h << 26))) & 0xffffffff
+    return h
+
+
+def compute_quadratic(items, hash_function):
+    # type: (Iterable[Any], Callable[[Any], int]) -> List[Any]
+    """
+    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.
+
+    :param items: Iterable set of items to place in hash table.
+    :param hash_function: Hash function which takes an item and returns a
+            number.
+
+    Simple example (see hash values above, they collide on slot 1):
+        >>> compute_quadratic(['Hello', 'world'], simple_hash)
+        [None, 'Hello', 'world', None]
+    """
+
+    items = list(items)
+    # Table size must be a power of two. Aim for >20% unused slots.
+    size = next_power_of_two(int(1.20*len(items)))
+    table = [None] * size  # type: List[Any]
+
+    for i in items:
+        h = hash_function(i) % size
+        s = 0
+        while table[h] is not None:
+            s += 1
+            h = (h + s) % size
+        table[h] = i
+
+    return table