Add 'ChaPRNG.h'

ChaPRNG.h

@@ -0,0 +1,88 @@
+#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];
+	}
+};