--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/druntime/src/compiler/dmd/arraycast.d	Tue Nov 11 01:52:37 2008 +0100
@@ -0,0 +1,109 @@
+/*
+ *  Copyright (C) 2004-2007 by Digital Mars, www.digitalmars.com
+ *  Written by Walter Bright
+ *
+ *  This software is provided 'as-is', without any express or implied
+ *  warranty. In no event will the authors be held liable for any damages
+ *  arising from the use of this software.
+ *
+ *  Permission is granted to anyone to use this software for any purpose,
+ *  including commercial applications, and to alter it and redistribute it
+ *  freely, in both source and binary form, subject to the following
+ *  restrictions:
+ *
+ *  o  The origin of this software must not be misrepresented; you must not
+ *     claim that you wrote the original software. If you use this software
+ *     in a product, an acknowledgment in the product documentation would be
+ *     appreciated but is not required.
+ *  o  Altered source versions must be plainly marked as such, and must not
+ *     be misrepresented as being the original software.
+ *  o  This notice may not be removed or altered from any source
+ *     distribution.
+ */
+
+/*
+ *  Modified by Sean Kelly for use with the D Runtime Project
+ */
+
+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);
+    }
+}
+
+}