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