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70 lines
2.0 KiB
C++
70 lines
2.0 KiB
C++
#include <Functions/FunctionFactory.h>
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#include <Functions/FunctionsRandom.h>
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#include <Common/HashTable/Hash.h>
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#include <Common/randomSeed.h>
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#include <common/unaligned.h>
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namespace DB
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{
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namespace
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{
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/// NOTE Probably
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/// http://www.pcg-random.org/
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/// or http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/SFMT/
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/// or http://docs.yeppp.info/c/group__yep_random___w_e_l_l1024a.html
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/// could go better.
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struct LinearCongruentialGenerator
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{
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/// Constants from `man lrand48_r`.
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static constexpr UInt64 a = 0x5DEECE66D;
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static constexpr UInt64 c = 0xB;
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/// And this is from `head -c8 /dev/urandom | xxd -p`
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UInt64 current = 0x09826f4a081cee35ULL;
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void seed(UInt64 value)
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{
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current = value;
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}
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UInt32 next()
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{
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current = current * a + c;
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return current >> 16;
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}
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};
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void seed(LinearCongruentialGenerator & generator, intptr_t additional_seed)
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{
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generator.seed(intHash64(randomSeed() ^ intHash64(additional_seed)));
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}
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}
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void RandImpl::execute(char * output, size_t size)
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{
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LinearCongruentialGenerator generator0;
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LinearCongruentialGenerator generator1;
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LinearCongruentialGenerator generator2;
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LinearCongruentialGenerator generator3;
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seed(generator0, 0xfb4121280b2ab902ULL + reinterpret_cast<intptr_t>(output));
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seed(generator1, 0x0121cf76df39c673ULL + reinterpret_cast<intptr_t>(output));
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seed(generator2, 0x17ae86e3a19a602fULL + reinterpret_cast<intptr_t>(output));
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seed(generator3, 0x8b6e16da7e06d622ULL + reinterpret_cast<intptr_t>(output));
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for (const char * end = output + size; output < end; output += 16)
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{
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unalignedStore<UInt32>(output, generator0.next());
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unalignedStore<UInt32>(output + 4, generator1.next());
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unalignedStore<UInt32>(output + 8, generator2.next());
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unalignedStore<UInt32>(output + 12, generator3.next());
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}
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/// It is guaranteed (by PaddedPODArray) that we can overwrite up to 15 bytes after end.
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}
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}
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