Move the 'meta' dir to 'lib/cretonne/meta'.

The 'lib/cretonne' directory will be the new root of a stand-alone
cretonne crate containg both Python and Rust sources.

This is in preparation for publishing crates on crates.io.

lib/cretonne/meta/unique_table.py

@@ -0,0 +1,68 @@
+"""
+Generate a table of unique items.
+
+The `UniqueTable` class collects items into an array, removing duplicates. Each
+item is mapped to its offset in the final array.
+
+This is a compression technique for compile-time generated tables.
+"""
+
+
+class UniqueTable:
+    """
+    Collect items into the `table` list, removing duplicates.
+    """
+    def __init__(self):
+        # List of items added in order.
+        self.table = list()
+        # Map item -> index.
+        self.index = dict()
+
+    def add(self, item):
+        """
+        Add a single item to the table if it isn't already there.
+
+        Return the offset into `self.table` of the item.
+        """
+        if item in self.index:
+            return self.index[item]
+
+        idx = len(self.table)
+        self.index[item] = idx
+        self.table.append(item)
+        return idx
+
+
+class UniqueSeqTable:
+    """
+    Collect sequences into the `table` list, removing duplicates.
+
+    Sequences don't have to be of the same length.
+    """
+    def __init__(self):
+        self.table = list()
+        # Map seq -> index.
+        self.index = dict()
+
+    def add(self, seq):
+        """
+        Add a sequence of items to the table. If the table already contains the
+        items in `seq` in the same order, use those instead.
+
+        Return the offset into `self.table` of the beginning of `seq`.
+        """
+        if len(seq) == 0:
+            return 0
+        seq = tuple(seq)
+        if seq in self.index:
+            return self.index[seq]
+
+        idx = len(self.table)
+        self.table.extend(seq)
+
+        # Add seq and all sub-sequences to `index`.
+        for length in range(1, len(seq) + 1):
+            for offset in range(len(seq) - length + 1):
+                self.index[seq[offset:offset+length]] = idx + offset
+
+        return idx