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      1 #include <math.h>
      2 #include <string.h>
      3 #include <inttypes.h>
      4 #include <stdio.h>
      5 #include <unistd.h>
      6 #include <sys/types.h>
      7 #include <fcntl.h>
      8 #include "ieee754.h"
      9 #include "zipf.h"
     10 #include "../minmax.h"
     11 #include "../hash.h"
     12 
     13 #define ZIPF_MAX_GEN	10000000UL
     14 
     15 static void zipf_update(struct zipf_state *zs)
     16 {
     17 	unsigned long to_gen;
     18 	unsigned int i;
     19 
     20 	/*
     21 	 * It can become very costly to generate long sequences. Just cap it at
     22 	 * 10M max, that should be doable in 1-2s on even slow machines.
     23 	 * Precision will take a slight hit, but nothing major.
     24 	 */
     25 	to_gen = min(zs->nranges, (uint64_t) ZIPF_MAX_GEN);
     26 
     27 	for (i = 0; i < to_gen; i++)
     28 		zs->zetan += pow(1.0 / (double) (i + 1), zs->theta);
     29 }
     30 
     31 static void shared_rand_init(struct zipf_state *zs, unsigned long nranges,
     32 			     unsigned int seed)
     33 {
     34 	memset(zs, 0, sizeof(*zs));
     35 	zs->nranges = nranges;
     36 
     37 	init_rand_seed(&zs->rand, seed, 0);
     38 	zs->rand_off = __rand(&zs->rand);
     39 }
     40 
     41 void zipf_init(struct zipf_state *zs, unsigned long nranges, double theta,
     42 	       unsigned int seed)
     43 {
     44 	shared_rand_init(zs, nranges, seed);
     45 
     46 	zs->theta = theta;
     47 	zs->zeta2 = pow(1.0, zs->theta) + pow(0.5, zs->theta);
     48 
     49 	zipf_update(zs);
     50 }
     51 
     52 unsigned long long zipf_next(struct zipf_state *zs)
     53 {
     54 	double alpha, eta, rand_uni, rand_z;
     55 	unsigned long long n = zs->nranges;
     56 	unsigned long long val;
     57 
     58 	alpha = 1.0 / (1.0 - zs->theta);
     59 	eta = (1.0 - pow(2.0 / n, 1.0 - zs->theta)) / (1.0 - zs->zeta2 / zs->zetan);
     60 
     61 	rand_uni = (double) __rand(&zs->rand) / (double) FRAND32_MAX;
     62 	rand_z = rand_uni * zs->zetan;
     63 
     64 	if (rand_z < 1.0)
     65 		val = 1;
     66 	else if (rand_z < (1.0 + pow(0.5, zs->theta)))
     67 		val = 2;
     68 	else
     69 		val = 1 + (unsigned long long)(n * pow(eta*rand_uni - eta + 1.0, alpha));
     70 
     71 	val--;
     72 
     73 	if (!zs->disable_hash)
     74 		val = __hash_u64(val);
     75 
     76 	return (val + zs->rand_off) % zs->nranges;
     77 }
     78 
     79 void pareto_init(struct zipf_state *zs, unsigned long nranges, double h,
     80 		 unsigned int seed)
     81 {
     82 	shared_rand_init(zs, nranges, seed);
     83 	zs->pareto_pow = log(h) / log(1.0 - h);
     84 }
     85 
     86 unsigned long long pareto_next(struct zipf_state *zs)
     87 {
     88 	double rand = (double) __rand(&zs->rand) / (double) FRAND32_MAX;
     89 	unsigned long long n;
     90 
     91 	n = (zs->nranges - 1) * pow(rand, zs->pareto_pow);
     92 
     93 	if (!zs->disable_hash)
     94 		n = __hash_u64(n);
     95 
     96 	return (n + zs->rand_off)  % zs->nranges;
     97 }
     98 
     99 void zipf_disable_hash(struct zipf_state *zs)
    100 {
    101 	zs->disable_hash = true;
    102 }
    103