--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/druntime/src/compiler/ldc/arraycast.d	Tue Jun 02 17:43:06 2009 +0100
@@ -0,0 +1,94 @@
+/**
+ * Implementation of array cast support routines.
+ *
+ * Copyright: Copyright Digital Mars 2004 - 2009.
+ * License:   <a href="http://www.boost.org/LICENSE_1_0.txt>Boost License 1.0</a>.
+ * Authors:   Walter Bright, Sean Kelly
+ *
+ *          Copyright Digital Mars 2004 - 2009.
+ * Distributed under the Boost Software License, Version 1.0.
+ *    (See accompanying file LICENSE_1_0.txt or copy at
+ *          http://www.boost.org/LICENSE_1_0.txt)
+ */
+module rt.arraycast;
+
+/******************************************
+ * Runtime helper to convert dynamic array of one
+ * type to dynamic array of another.
+ * Adjusts the length of the array.
+ * Throws exception if new length is not aligned.
+ */
+
+extern (C)
+
+void[] _d_arraycast(size_t tsize, size_t fsize, void[] a)
+{
+    auto length = a.length;
+
+    auto nbytes = length * fsize;
+    if (nbytes % tsize != 0)
+    {
+    throw new Exception("array cast misalignment");
+    }
+    length = nbytes / tsize;
+    *cast(size_t *)&a = length; // jam new length
+    return a;
+}
+
+unittest
+{
+    byte[int.sizeof * 3] b;
+    int[] i;
+    short[] s;
+
+    i = cast(int[])b;
+    assert(i.length == 3);
+
+    s = cast(short[])b;
+    assert(s.length == 6);
+
+    s = cast(short[])i;
+    assert(s.length == 6);
+}
+
+/******************************************
+ * Runtime helper to convert dynamic array of bits
+ * dynamic array of another.
+ * Adjusts the length of the array.
+ * Throws exception if new length is not aligned.
+ */
+
+version (none)
+{
+extern (C)
+
+void[] _d_arraycast_frombit(uint tsize, void[] a)
+{
+    uint length = a.length;
+
+    if (length & 7)
+    {
+    throw new Exception("bit[] array cast misalignment");
+    }
+    length /= 8 * tsize;
+    *cast(size_t *)&a = length; // jam new length
+    return a;
+}
+
+unittest
+{
+    version (D_Bits)
+    {
+    bit[int.sizeof * 3 * 8] b;
+    int[] i;
+    short[] s;
+
+    i = cast(int[])b;
+    assert(i.length == 3);
+
+    s = cast(short[])b;
+    assert(s.length == 6);
+    }
+}
+
+}