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Simplified SDL random function names and added thread-safe versions

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This commit is contained in:
Sam Lantinga
2024-06-23 12:11:33 -07:00
parent d013ac80ef
commit 96f2f23240
12 changed files with 167 additions and 90 deletions
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35
src/stdlib/SDL_random.c
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@@ -34,12 +34,30 @@ void SDL_srand(Uint64 seed)
SDL_rand_initialized = SDL_TRUE;
}
Uint32 SDL_rand_bits(void)
Sint32 SDL_rand(Sint32 n)
{
if (!SDL_rand_initialized) {
SDL_srand(0);
}
return SDL_rand_r(&SDL_rand_state, n);
}
float SDL_randf(void)
{
if (!SDL_rand_initialized) {
SDL_srand(0);
}
return SDL_randf_r(&SDL_rand_state);
}
Uint32 SDL_rand_bits_r(Uint64 *state)
{
if (!state) {
return 0;
}
// The C and A parameters of this LCG have been chosen based on hundreds
// of core-hours of testing with PractRand and TestU01's Crush.
// Using a 32-bit A improves performance on 32-bit architectures.
@@ -55,13 +73,13 @@ Uint32 SDL_rand_bits(void)
// Softw Pract Exper. 2022;52(2):443-458. doi: 10.1002/spe.3030
// https://arxiv.org/abs/2001.05304v2
SDL_rand_state = SDL_rand_state * 0xff1cd035ul + 0x05;
*state = *state * 0xff1cd035ul + 0x05;
// Only return top 32 bits because they have a longer period
return (Uint32)(SDL_rand_state >> 32);
return (Uint32)(*state >> 32);
}
Sint32 SDL_rand_n(Sint32 n)
Sint32 SDL_rand_r(Uint64 *state, Sint32 n)
{
// Algorithm: get 32 bits from SDL_rand_bits() and treat it as a 0.32 bit
// fixed point number. Multiply by the 31.0 bit n to get a 31.32 bit
@@ -70,18 +88,19 @@ Sint32 SDL_rand_n(Sint32 n)
if (n < 0) {
// The algorithm looks like it works for numbers < 0 but it has an
// infintesimal chance of returning a value out of range.
// Returning -SDL_rand_n(abs(n)) blows up at INT_MIN instead.
// Returning -SDL_rand(abs(n)) blows up at INT_MIN instead.
// It's easier to just say no.
return 0;
}
// On 32-bit arch, the compiler will optimize to a single 32-bit multiply
Uint64 val = (Uint64)SDL_rand_bits() * n;
Uint64 val = (Uint64)SDL_rand_bits_r(state) * n;
return (Sint32)(val >> 32);
}
float SDL_rand_float(void)
float SDL_randf_r(Uint64 *state)
{
// Note: its using 24 bits because float has 23 bits significand + 1 implicit bit
return (SDL_rand_bits() >> (32 - 24)) * 0x1p-24f;
return (SDL_rand_bits_r(state) >> (32 - 24)) * 0x1p-24f;
}