1 /**
2  * Implementation of array cast support routines.
3  *
4  * Copyright: Copyright Digital Mars 2004 - 2016.
5  * License:   Distributed under the
6  *            $(LINK2 http://www.boost.org/LICENSE_1_0.txt, Boost Software License 1.0).
7  * Authors:   Walter Bright, Sean Kelly
8  * Source:    $(DRUNTIMESRC src/rt/_arraycast.d)
9  */
10 
11 module rt.arraycast;
12 
13 /******************************************
14  * Runtime helper to convert dynamic array of one
15  * type to dynamic array of another.
16  * Adjusts the length of the array.
17  * Throws an error if new length is not aligned.
18  */
19 
20 extern (C)
21 
22 @trusted nothrow
_d_arraycast(size_t tsize,size_t fsize,void[]a)23 void[] _d_arraycast(size_t tsize, size_t fsize, void[] a)
24 {
25     auto length = a.length;
26 
27     auto nbytes = length * fsize;
28     if (nbytes % tsize != 0)
29     {
30         throw new Error("array cast misalignment");
31     }
32     length = nbytes / tsize;
33     *cast(size_t *)&a = length; // jam new length
34     return a;
35 }
36 
37 unittest
38 {
39     byte[int.sizeof * 3] b;
40     int[] i;
41     short[] s;
42 
43     i = cast(int[])b;
44     assert(i.length == 3);
45 
46     s = cast(short[])b;
47     assert(s.length == 6);
48 
49     s = cast(short[])i;
50     assert(s.length == 6);
51 }
52 
53