REVIEWED: GetRandomValue(), explained the new approach to get more uniform random values range

This commit is contained in:
Ray
2025-12-10 09:30:18 +01:00
parent f2a900a60d
commit bc2057345b

View File

@@ -1743,20 +1743,23 @@ int GetRandomValue(int min, int max)
TRACELOG(LOG_WARNING, "Invalid GetRandomValue() arguments, range should not be higher than %i", RAND_MAX); TRACELOG(LOG_WARNING, "Invalid GetRandomValue() arguments, range should not be higher than %i", RAND_MAX);
} }
// NOTE: This one-line approach produces a non-uniform distribution,
// as stated by Donald Knuth in the book The Art of Programming, so
// using below approach for more uniform results
//value = (rand()%(abs(max - min) + 1) + min);
// More uniform range solution
int range = (max - min) + 1; int range = (max - min) + 1;
// Degenerate/overflow case: fall back to min (same behavior as "always min" instead of UB) // Degenerate/overflow case: fall back to min (same behavior as "always min" instead of UB)
if (range <= 0) if (range <= 0) value = min;
{
value = min;
}
else else
{ {
// Rejection sampling to get a uniform integer in [min, max] // Rejection sampling to get a uniform integer in [min, max]
unsigned long c = (unsigned long)RAND_MAX + 1UL; // number of possible rand() results unsigned long c = (unsigned long)RAND_MAX + 1UL; // number of possible rand() results
unsigned long m = (unsigned long)range; // size of the target interval unsigned long m = (unsigned long)range; // size of the target interval
unsigned long t = c - (c%m); // largest multiple of m <= c unsigned long t = c - (c%m); // largest multiple of m <= c
unsigned long r; unsigned long r = 0;
for (;;) for (;;)
{ {
@@ -1764,7 +1767,6 @@ int GetRandomValue(int min, int max)
if (r < t) break; // Only accept values within the fair region if (r < t) break; // Only accept values within the fair region
} }
value = min + (int)(r%m); value = min + (int)(r%m);
} }
#endif #endif