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145
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1 /**
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2 * Implementation of array cast support routines.
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3 *
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4 * Copyright: Copyright Digital Mars 2004 - 2016.
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5 * License: Distributed under the
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6 * $(LINK2 http://www.boost.org/LICENSE_1_0.txt, Boost Software License 1.0).
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7 * Authors: Walter Bright, Sean Kelly
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8 * Source: $(DRUNTIMESRC src/rt/_arraycast.d)
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9 */
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10
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11 module rt.arraycast;
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12
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13 /******************************************
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14 * Runtime helper to convert dynamic array of one
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15 * type to dynamic array of another.
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16 * Adjusts the length of the array.
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17 * Throws an error if new length is not aligned.
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18 */
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19
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20 extern (C)
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21
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22 @trusted nothrow
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23 void[] _d_arraycast(size_t tsize, size_t fsize, void[] a)
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24 {
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25 auto length = a.length;
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26
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27 auto nbytes = length * fsize;
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28 if (nbytes % tsize != 0)
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29 {
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30 throw new Error("array cast misalignment");
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31 }
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32 length = nbytes / tsize;
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33 *cast(size_t *)&a = length; // jam new length
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34 return a;
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35 }
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36
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37 unittest
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38 {
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39 byte[int.sizeof * 3] b;
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40 int[] i;
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41 short[] s;
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42
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43 i = cast(int[])b;
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44 assert(i.length == 3);
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45
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46 s = cast(short[])b;
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47 assert(s.length == 6);
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48
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49 s = cast(short[])i;
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50 assert(s.length == 6);
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51 }
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52
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