Atmosphere/stratosphere/loader/source/ldr_random.cpp

50 lines
1.2 KiB
C++

#include <switch.h>
#include "ldr_random.hpp"
/* Official HOS uses TinyMT. This is high effort. Let's just use XorShift. */
/* https://en.wikipedia.org/wiki/Xorshift */
static u32 g_random_state[4] = {0};
static bool g_has_initialized = false;
static void EnsureRandomState() {
if (g_has_initialized) {
return;
}
/* Retrieve process entropy with svcGetInfo. */
u64 val = 0;
for (unsigned int i = 0; i < 4; i++) {
if (R_FAILED(svcGetInfo(&val, 0xB, 0, i))) {
/* TODO: Panic? */
}
g_random_state[i] = val & 0xFFFFFFFF;
}
g_has_initialized = true;
}
u32 RandomUtils::GetNext() {
EnsureRandomState();
u32 s, t = g_random_state[3];
t ^= t << 11;
t ^= t >> 8;
g_random_state[3] = g_random_state[2]; g_random_state[2] = g_random_state[1]; g_random_state[1] = (s = g_random_state[0]);
t ^= s;
t ^= s >> 19;
g_random_state[0] = t;
return t;
}
/* These are slightly biased, but I think that's totally okay. */
u32 RandomUtils::GetRandomU32(u32 max) {
return GetNext() % max;
}
u64 RandomUtils::GetRandomU64(u64 max) {
u64 val = GetNext();
val |= ((u64)GetNext()) << 32;
return val % max;
}