53 lines
1.1 KiB
C++
53 lines
1.1 KiB
C++
#include <kernel/CPUID.h>
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#include <kernel/Debug.h>
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#include <kernel/Random.h>
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#include <kernel/Timer/Timer.h>
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namespace Kernel
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{
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// Constants and algorithm from https://en.wikipedia.org/wiki/Permuted_congruential_generator
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static uint64_t s_rand_seed = 0x4d595df4d0f33173;
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static constexpr uint64_t s_rand_multiplier = 6364136223846793005;
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static constexpr uint64_t s_rand_increment = 1442695040888963407;
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void Random::initialize()
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{
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uint32_t ecx, edx;
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CPUID::get_features(ecx, edx);
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if (ecx & CPUID::ECX_RDRND)
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{
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asm volatile("rdrand %0" : "=a"(s_rand_seed));
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dprintln("RNG seeded by RDRAND");
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}
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else
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{
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auto rt = SystemTimer::get().real_time();
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s_rand_seed ^= rt.tv_sec ^ rt.tv_nsec;
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dprintln("RNG seeded by real time");
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}
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}
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uint32_t Random::get_u32()
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{
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auto rotr32 = [](uint32_t x, unsigned r) { return x >> r | x << (-r & 31); };
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uint64_t x = s_rand_seed;
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unsigned count = (unsigned)(x >> 59);
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s_rand_seed = x * s_rand_multiplier + s_rand_increment;
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x ^= x >> 18;
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return rotr32(x >> 27, count) % UINT32_MAX;
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}
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uint64_t Random::get_u64()
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{
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return ((uint64_t)get_u32() << 32) | get_u32();
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}
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}
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