forked from KolibriOS/kolibrios
168 lines
2.7 KiB
C++
168 lines
2.7 KiB
C++
#include <float.h>
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// TODO: use large period prng
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static uint64_t seed = -1;
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static uint32_t rand32(void)
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{
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seed = 6364136223846793005ULL*seed + 1;
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return seed >> 32;
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}
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static uint64_t rand64(void)
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{
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uint64_t u = rand32();
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return u<<32 | rand32();
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}
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static double frand()
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{
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return rand64() * 0x1p-64;
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}
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static float frandf()
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{
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return rand32() * 0x1p-32f;
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}
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static long double frandl()
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{
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return rand64() * 0x1p-64L
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#if LDBL_MANT_DIG > 64
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+ rand64() * 0x1p-128L
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#endif
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;
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}
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void t_randseed(uint64_t s)
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{
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seed = s;
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}
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/* uniform random in [0,n), n > 0 must hold */
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uint64_t t_randn(uint64_t n)
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{
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uint64_t r, m;
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/* m is the largest multiple of n */
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m = -1;
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m -= m%n;
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while ((r = rand64()) >= m);
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return r%n;
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}
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/* uniform on [a,b], a <= b must hold */
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uint64_t t_randint(uint64_t a, uint64_t b)
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{
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uint64_t n = b - a + 1;
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if (n)
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return a + t_randn(n);
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return rand64();
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}
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/* shuffle the elements of p and q until the elements in p are well shuffled */
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static void shuffle2(uint64_t *p, uint64_t *q, size_t np, size_t nq)
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{
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size_t r;
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uint64_t t;
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while (np) {
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r = t_randn(nq+np--);
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t = p[np];
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if (r < nq) {
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p[np] = q[r];
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q[r] = t;
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} else {
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p[np] = p[r-nq];
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p[r-nq] = t;
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}
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}
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}
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/* shuffle the elements of p */
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void t_shuffle(uint64_t *p, size_t n)
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{
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shuffle2(p,0,n,0);
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}
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void t_randrange(uint64_t *p, size_t n)
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{
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size_t i;
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for (i = 0; i < n; i++)
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p[i] = i;
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t_shuffle(p, n);
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}
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/* hash table insert, 0 means empty, v > 0 must hold, len is power-of-2 */
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static int insert(uint64_t *tab, size_t len, uint64_t v)
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{
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size_t i = v & (len-1);
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size_t j = 1;
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while (tab[i]) {
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if (tab[i] == v)
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return -1;
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i += j++;
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i &= len-1;
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}
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tab[i] = v;
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return 0;
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}
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/* choose k unique numbers from [0,n), k <= n */
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int t_choose(uint64_t n, size_t k, uint64_t *p)
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{
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uint64_t *tab;
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size_t i, j, len;
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if (n < k)
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return -1;
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if (n < 16) {
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/* no alloc */
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while (k)
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if (t_randn(n--) < k)
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p[--k] = n;
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return 0;
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}
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if (k < 8) {
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/* no alloc, n > 15 > 2*k */
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for (i = 0; i < k;) {
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p[i] = t_randn(n);
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for (j = 0; p[j] != p[i]; j++);
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if (j == i)
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i++;
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}
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return 0;
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}
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// TODO: if k < n/k use k*log(k) solution without alloc
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if (n < 5*k && (n-k)*sizeof *tab < (size_t)-1) {
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/* allocation is n-k < 4*k */
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tab = malloc((n-k) * sizeof *tab);
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if (!tab)
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return -1;
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for (i = 0; i < k; i++)
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p[i] = i;
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for (; i < n; i++)
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tab[i-k] = i;
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if (k < n-k)
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shuffle2(p, tab, k, n-k);
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else
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shuffle2(tab, p, n-k, k);
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free(tab);
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return 0;
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}
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/* allocation is 2*k <= len < 4*k */
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for (len = 16; len < 2*k; len *= 2);
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tab = calloc(len, sizeof *tab);
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if (!tab)
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return -1;
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for (i = 0; i < k; i++)
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while (insert(tab, len, t_randn(n)+1));
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for (i = 0; i < len; i++)
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if (tab[i])
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*p++ = tab[i]-1;
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free(tab);
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return 0;
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}
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