Random Utilities¶

Deterministic random number generation with an explicit seed, plus convenience pickers and shuffles. The RNG is rand() based; call seed or random_seed to control it.

#include "abscom/abs.h"

Seeding¶

Function	Description
`void seed(var obj)`	Seed the RNG from an int value or the hash of a string value.
`void random_seed(void)`	Seed from the current time.

seed(v(42));       /* reproducible sequence */
random_seed();     /* different every run  */

Numbers¶

Function	Description
`var randint(int min, int max)`	Uniform random int in `[min, max]` (bounds auto-swap).
`var random_float(void)`	Uniform float in `[0.0, 1.0)`.
`var uniform(double a, double b)`	Uniform float in `[a, b]`.

Collections¶

Function	Description
`var choice(var seq)`	A random item from a non-empty list, or a random char from a string.
`var choices(var seq, int k)`	A new list of `k` random items/chars (repetition allowed).
`var sample(var seq, int k)`	A new list of `k` unique random items (lists only).
`void shuffle(var list)`	Randomize a list in place (returns nothing).
`void fisher_yates(var list)`	Same algorithm as `shuffle`, under its classic name.
`void riffle_shuffle(var list)`	In-place shuffle that splits the list in half and randomly interleaves the two piles (a card-deck riffle).

Empty-sequence choice/choices and k-too-large sample produce ABS_ERROR. sample, shuffle, fisher_yates, and riffle_shuffle accept lists only; on non-lists they are no-ops.

Example¶

abs_init();
seed(v(42));

print(randint(1, 100));       /* deterministic given seed */
print(random_float());
print(uniform(10.0, 20.0));

var xs   = range(0, 10);      /* [0..9] */
print(choice(xs));
print(choices(xs, 5));

var uniq = sample(xs, 3);     /* new list, 3 unique items */
shuffle(xs);                  /* xs itself is permuted  */
print(uniq);
print(xs);

var deck = range(0, 13);      /* a hand of cards... */
riffle_shuffle(deck);         /* ...cut and interleaved */
fisher_yates(deck);           /* ...or fully randomized */
print(deck);

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