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LibC: Add drand48, srand48

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These functions are required for the `perl5` port's random function to
operate correctly. As a bonus, this allows us to remove a nasty patch
that replaces `drand48` with `random`.
This commit is contained in:
Beckett Normington 2023-08-25 12:20:39 -04:00 • committed by Tim Schumacher
commit 8bc1f1b63e
Notes: sideshowbarker 2024-07-16 23:57:20 +09:00
2 changed files with 20 additions and 0 deletions
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18
Userland/Libraries/LibC/stdlib.cpp
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@ -657,6 +657,7 @@ int ptsname_r(int fd, char* buffer, size_t size)
}
static unsigned long s_next_rand = 1;
static long s_next_rand48 = 0;
// https://pubs.opengroup.org/onlinepubs/9699919799/functions/rand.html
int rand()
@ -671,6 +672,23 @@ void srand(unsigned seed)
s_next_rand = seed;
}
// https://pubs.opengroup.org/onlinepubs/9699919799/functions/drand48.html
double drand48()
{
constexpr u64 a = 0x5DEECE66DULL;
constexpr u64 c = 0xBULL;
constexpr u64 m = 1ULL << 48;
s_next_rand48 = (a * s_next_rand48 + c) & (m - 1);
return static_cast<double>(s_next_rand48) / m;
}
// https://pubs.opengroup.org/onlinepubs/9699919799/functions/srand48.html
void srand48(long seed)
{
s_next_rand48 = (seed & 0xFFFFFFFF) << 16 | 0x330E;
}
// https://pubs.opengroup.org/onlinepubs/9699919799/functions/abs.html
int abs(int i)
{