forked from 0ad/0ad
janwas
c0ed950657
this snowballed into a massive search+destroy of the hodgepodge of mostly equivalent types we had in use (int, uint, unsigned, unsigned int, i32, u32, ulong, uintN). it is more efficient to use 64-bit types in 64-bit mode, so the preferred default is size_t (for anything remotely resembling a size or index). tile coordinates are ssize_t to allow more efficient conversion to/from floating point. flags are int because we almost never need more than 15 distinct bits, bit test/set is not slower and int is fastest to type. finally, some data that is pretty much directly passed to OpenGL is now typed accordingly. after several hours, the code now requires fewer casts and less guesswork. other changes: - unit and player IDs now have an "invalid id" constant in the respective class to avoid casting and -1 - fix some endian/64-bit bugs in the map (un)packing. added a convenience function to write/read a size_t. - ia32: change CPUID interface to allow passing in ecx (required for cache topology detection, which I need at work). remove some unneeded functions from asm, replace with intrinsics where possible. This was SVN commit r5942.
65 lines
1.8 KiB
C++
65 lines
1.8 KiB
C++
/**
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* =========================================================================
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* File : rand.cpp
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* Project : 0 A.D.
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* Description : pseudorandom number generator
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* =========================================================================
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*/
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// license: GPL; see lib/license.txt
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#include "precompiled.h"
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#include "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_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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debug_assert(x < max_exclusive);
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return x;
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}
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