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Add 'ChaPRNG.h'

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      ChaPRNG.h

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ChaPRNG.h Bestand weergeven

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#pragma once
#include <array>
#include <algorithm>
#include <cstdint>
#define ROTL(a,b) (((a) << (b)) | ((a) >> (32 - (b))))
#define QR(a, b, c, d) ( \
a += b, d ^= a, d = ROTL(d,16), \
c += d, b ^= c, b = ROTL(b,12), \
a += b, d ^= a, d = ROTL(d, 8), \
c += d, b ^= c, b = ROTL(b, 7))
//
// Based on code from RFC 7539
//
template<int ROUNDS>
void chacha_do_rounds(std::array<uint32_t, 16>& out) {
static_assert(ROUNDS%2 == 0, "ChaPRNG: Rounds count MUST be even.");
for (int i = 0; i < ROUNDS; i += 2) {
// Odd round
QR(out[0], out[4], out[ 8], out[12]); // column 0
QR(out[1], out[5], out[ 9], out[13]); // column 1
QR(out[2], out[6], out[10], out[14]); // column 2
QR(out[3], out[7], out[11], out[15]); // column 3
// Even round
QR(out[0], out[5], out[10], out[15]); // diagonal 1 (main diagonal)
QR(out[1], out[6], out[11], out[12]); // diagonal 2
QR(out[2], out[7], out[ 8], out[13]); // diagonal 3
QR(out[3], out[4], out[ 9], out[14]); // diagonal 4
}
}
template<int ROUNDS, bool REMIX = true, bool DIRECT = false>
std::array<uint32_t, 16> chacha_block(std::array<uint32_t, 16>& in)
{
std::array<uint32_t, 16> out;
int i;
if constexpr(DIRECT) {
chacha_do_rounds<ROUNDS>(in);
return out;
}else {
for (i = 0; i < 16; ++i)
out[i] = in[i];
chacha_do_rounds<ROUNDS>(out);
if constexpr(REMIX) {
for (i = 0; i < 16; ++i)
out[i] += in[i];
}
return out;
}
}
template<int ROUNDS, bool REMIX = true, bool DIRECT = false>
class ChaPRNG {
std::array<uint32_t, 16> source;
std::array<uint32_t, 16> current;
uint32_t it = 0;
public:
ChaPRNG(std::array<uint32_t, 12> seed = {0}) {
source[0] = 'expa';
source[1] = 'nd 3';
source[2] = '2-by';
source[3] = 'te k';
std::copy(seed.begin(), seed.end(), source.begin()+4);
}
uint32_t operator()() {
auto spot = it & 0b1111;
if(spot == 0) {
source[12]++;
if constexpr (DIRECT) {
chacha_block<ROUNDS, REMIX, DIRECT>(source);
} else {
current = chacha_block<ROUNDS, REMIX, DIRECT>(source);
}
}
++it;
if constexpr (DIRECT)
return source[spot];
else
return current[spot];
}
};

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