util/random/fast.cpp


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#include "fast.h" 
 
#include <util/stream/input.h> 
 
static inline ui32 FixSeq(ui32 seq1, ui32 seq2) noexcept {
    const ui32 mask = (~(ui32)(0)) >> 1; 
 
    if ((seq1 & mask) == (seq2 & mask)) { 
        return ~seq2; 
    } 
 
    return seq2; 
} 
 
TFastRng64::TFastRng64(ui64 seed1, ui32 seq1, ui64 seed2, ui32 seq2) noexcept
    : R1_(seed1, seq1) 
    , R2_(seed2, FixSeq(seq1, seq2)) 
{ 
} 
 
TFastRng64::TArgs::TArgs(ui64 seed) noexcept {
    TReallyFastRng32 rng(seed); 
 
    Seed1 = rng.GenRand64(); 
    Seq1 = rng.GenRand(); 
    Seed2 = rng.GenRand64(); 
    Seq2 = rng.GenRand(); 
} 
 
TFastRng64::TArgs::TArgs(IInputStream& entropy) {
    static_assert(sizeof(*this) == 3 * sizeof(ui64), "please, fix me"); 
    entropy.LoadOrFail(this, sizeof(*this)); 
} 
 
template <class T> 
static inline T Read(IInputStream& in) noexcept {
    T t = T(); 
 
    in.LoadOrFail(&t, sizeof(t)); 
 
    return t; 
} 
 
TFastRng32::TFastRng32(IInputStream& entropy)
    : TFastRng32(Read<ui64>(entropy), Read<ui32>(entropy)) 
{ 
} 
 
TReallyFastRng32::TReallyFastRng32(IInputStream& entropy)
    : TReallyFastRng32(Read<ui64>(entropy)) 
{ 
}