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src/game/prng.cpp
54 строки
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Chairn
Huge variable naming format
08 июл 2022, 19:01
08 июл 2022, 19:01
a69dc59
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#include "prng.h" #include <base/system.h> // From https://en.wikipedia.org/w/index.php?title=Permuted_congruential_generator&oldid=901497400#Example_code. // // > The generator recommended for most users is PCG-XSH-RR with 64-bit state // > and 32-bit output. #define NAME "pcg-xsh-rr" CPrng::CPrng() : m_Seeded(false) { } const char *CPrng::Description() const { if(!m_Seeded) { return NAME ":unseeded"; } return m_aDescription; } static unsigned int RotateRight32(unsigned int x, int Shift) { return (x >> Shift) | (x << (-Shift & 31)); } void CPrng::Seed(uint64_t aSeed[2]) { m_Seeded = true; str_format(m_aDescription, sizeof(m_aDescription), "%s:%08x%08x:%08x%08x", NAME, (unsigned)(aSeed[0] >> 32), (unsigned)aSeed[0], (unsigned)(aSeed[1] >> 32), (unsigned)aSeed[1]); m_Increment = (aSeed[1] << 1) | 1; m_State = aSeed[0] + m_Increment; RandomBits(); } unsigned int CPrng::RandomBits() { dbg_assert(m_Seeded, "prng needs to be seeded before it can generate random numbers"); uint64_t x = m_State; unsigned int Count = x >> 59; static const uint64_t s_Multiplier = 6364136223846793005u; m_State = x * s_Multiplier + m_Increment; x ^= x >> 18; return RotateRight32(x >> 27, Count); }