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145
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1 /**
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2 * Random number generators for internal usage.
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3 *
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4 * Copyright: Copyright Digital Mars 2014.
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5 * License: $(WEB www.boost.org/LICENSE_1_0.txt, Boost License 1.0).
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6 */
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7 module rt.util.random;
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8
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9 struct Rand48
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10 {
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11 private ulong rng_state;
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12
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13 @safe @nogc nothrow:
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14
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15 void defaultSeed()
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16 {
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17 import ctime = core.stdc.time : time;
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18 seed(cast(uint)ctime.time(null));
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19 }
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20
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21 pure:
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22
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23 void seed(uint seedval)
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24 {
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25 assert(seedval);
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26 rng_state = cast(ulong)seedval << 16 | 0x330e;
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27 popFront();
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28 }
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29
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30 auto opCall()
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31 {
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32 auto result = front;
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33 popFront();
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34 return result;
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35 }
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36
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37 @property uint front()
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38 {
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39 return cast(uint)(rng_state >> 16);
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40 }
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41
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42 void popFront()
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43 {
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44 immutable ulong a = 25214903917;
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45 immutable ulong c = 11;
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46 immutable ulong m_mask = (1uL << 48uL) - 1;
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47 rng_state = (a*rng_state+c) & m_mask;
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48 }
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49
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50 enum empty = false;
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51 }
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