elexis
43137fef3f
Differential Revision: https://code.wildfiregames.com/D716
Refs 09e974e1cb
Reviewed By: bb
Change in agreement with leper.
This was SVN commit r19899.
81 lines
2.5 KiB
C++
81 lines
2.5 KiB
C++
/* Copyright (C) 2010 Wildfire Games.
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be included
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* in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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/*
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* pseudorandom number generator
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*/
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#include "precompiled.h"
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#include "lib/rand.h"
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// avoids several common pitfalls; see discussion at
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// http://www.azillionmonkeys.com/qed/random.html
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// rand() is poorly implemented (e.g. in VC7) and only returns < 16 bits;
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// double that amount by concatenating 2 random numbers.
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// this is not to fix poor rand() randomness - the number returned will be
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// folded down to a much smaller interval anyway. instead, a larger XRAND_MAX
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// decreases the probability of having to repeat the loop.
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#if RAND_MAX < 65536
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static const size_t XRAND_MAX = (RAND_MAX+1)*(RAND_MAX+1) - 1;
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static size_t xrand()
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{
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return rand()*(RAND_MAX+1) + rand();
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}
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// rand() is already ok; no need to do anything.
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#else
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static const size_t XRAND_MAX = RAND_MAX;
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static size_t xrand()
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{
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return rand();
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}
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#endif
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size_t rand(size_t min_inclusive, size_t max_exclusive)
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{
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const size_t range = (max_exclusive-min_inclusive);
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// huge interval or min >= max
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if(range == 0 || range > XRAND_MAX)
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{
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WARN_IF_ERR(ERR::INVALID_PARAM);
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return 0;
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}
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const size_t inv_range = XRAND_MAX / range;
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// generate random number in [0, range)
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// idea: avoid skewed distributions when <range> doesn't evenly divide
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// XRAND_MAX by simply discarding values in the "remainder".
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// not expected to run often since XRAND_MAX is large.
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size_t x;
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do
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{
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x = xrand();
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}
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while(x >= range * inv_range);
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x /= inv_range;
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x += min_inclusive;
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ENSURE(x < max_exclusive);
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return x;
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}
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