Kernel: Implement super simple PRNG

kernel/CMakeLists.txt

@@ -64,6 +64,7 @@ set(KERNEL_SOURCES
 	kernel/PCI.cpp
 	kernel/PIC.cpp
 	kernel/Process.cpp
+	kernel/Random.cpp
 	kernel/Scheduler.cpp
 	kernel/Semaphore.cpp
 	kernel/SpinLock.cpp

kernel/include/kernel/Random.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <stdint.h>
+
+namespace Kernel
+{
+
+	class Random
+	{
+	public:
+		static void initialize();
+		static uint32_t get_u32();
+		static uint64_t get_u64();
+	};
+
+}

kernel/kernel/Random.cpp

@@ -0,0 +1,44 @@
+#include <kernel/Debug.h>
+#include <kernel/CPUID.h>
+#include <kernel/Random.h>
+
+namespace Kernel
+{
+
+
+	// Constants and algorithm from https://en.wikipedia.org/wiki/Permuted_congruential_generator
+
+	static uint64_t s_rand_seed = 0x4d595df4d0f33173;
+	static constexpr uint64_t s_rand_multiplier = 6364136223846793005;
+	static constexpr uint64_t s_rand_increment = 1442695040888963407;
+
+	void Random::initialize()
+	{
+		uint32_t ecx, edx;
+		CPUID::get_features(ecx, edx);
+
+		if (ecx & CPUID::ECX_RDRND)
+			asm volatile("rdrand %0" : "=a"(s_rand_seed));
+		else
+			dprintln("No RDRAND available");
+	}
+
+	uint32_t Random::get_u32()
+	{
+		auto rotr32 = [](uint32_t x, unsigned r) { return x >> r | x << (-r & 31); };
+
+		uint64_t x = s_rand_seed;
+		unsigned count = (unsigned)(x >> 59);
+
+		s_rand_seed = x * s_rand_multiplier + s_rand_increment;
+		x ^= x >> 18;
+
+		return rotr32(x >> 27, count) % UINT32_MAX;
+	}
+
+	uint64_t Random::get_u64()
+	{
+		return ((uint64_t)get_u32() << 32) | get_u32();
+	}
+
+}

kernel/kernel/kernel.cpp

@@ -19,6 +19,7 @@
 #include <kernel/PCI.h>
 #include <kernel/PIC.h>
 #include <kernel/Process.h>
+#include <kernel/Random.h>
 #include <kernel/Scheduler.h>
 #include <kernel/Syscall.h>
 #include <kernel/Terminal/Serial.h>
@@ -153,6 +154,9 @@ extern "C" void kernel_main(uint32_t boot_magic, uint32_t boot_info)
 		dprintln("Virtual TTY initialized");
 	}
 
+	Random::initialize();
+	dprintln("RNG initialized");
+
 	MUST(Scheduler::initialize());
 	dprintln("Scheduler initialized");