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LibC: Cleanup RNG and properly initialize to srand(1) at startup

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Bananymous
2026-04-21 00:26:41 +03:00
parent ea4c34fc0b
commit eea0154f18
1 changed files with 18 additions and 12 deletions
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30
userspace/libraries/LibC/stdlib.cpp
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@@ -828,35 +828,40 @@ void qsort(void* base, size_t nel, size_t width, int (*compar)(const void*, cons
// Constants and algorithm from https://en.wikipedia.org/wiki/Permuted_congruential_generator
static uint64_t s_rand_state = 0x4d595df4d0f33173;
static constexpr uint64_t s_rand_multiplier = 6364136223846793005;
static constexpr uint64_t s_rand_increment = 1442695040888963407;
static uint64_t s_rand_state;
static constexpr uint32_t rotr32(uint32_t x, unsigned r)
{
return x >> r | x << (-r & 31);
}
int rand_r(unsigned* seed)
template<BAN::integral T>
static inline int rand_impl(T& state)
{
uint64_t x = *seed | (static_cast<uint64_t>(*seed) << 32);
unsigned count = (unsigned)(x >> 59);
uint64_t x;
if constexpr (sizeof(T) == 8) x = state;
if constexpr (sizeof(T) == 4) x = state * 0x0000000100000001;
if constexpr (sizeof(T) == 2) x = state * 0x0001000100010001;
if constexpr (sizeof(T) == 1) x = state * 0x0101010101010101;
*seed = x * s_rand_multiplier + s_rand_increment;
const unsigned count = x >> 59;
state = x * s_rand_multiplier + s_rand_increment;
x ^= x >> 18;
return rotr32(x >> 27, count) % RAND_MAX;
}
int rand_r(unsigned* seed)
{
return rand_impl(*seed);
}
int rand(void)
{
uint64_t x = s_rand_state;
unsigned count = (unsigned)(x >> 59);
s_rand_state = x * s_rand_multiplier + s_rand_increment;
x ^= x >> 18;
return rotr32(x >> 27, count) % RAND_MAX;
return rand_impl(s_rand_state);
}
void srand(unsigned int seed)
@@ -953,4 +958,5 @@ void init_default_random()
{
static char buffer[128];
initstate(1, buffer, 128);
srand(1);
}