133 lines
2.8 KiB
C
133 lines
2.8 KiB
C
/*
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* zipfian distribution copied from YCSB
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* https://github.com/brianfrankcooper/YCSB
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <math.h>
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#include <time.h>
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#include "zipf.h"
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/* global static */
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static int items;
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static int base;
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static double zipfianconstant;
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static double alpha, zetan, eta, theta, zeta2theta;
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static int countforzeta;
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static int allowitemcountdecrease = 0;
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/* declarations */
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double zetastatic2(int st, int n, double theta, double initialsum);
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double zeta2(int st, int n, double theta_val, double initialsum);
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double zetastatic(int n, double theta);
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double zeta(int n, double theta_val);
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double rand_double() {
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return (double)rand() / (double)RAND_MAX;
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}
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int next_int(int itemcount) {
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double u, uz;
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int ret;
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if (itemcount != countforzeta) {
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zetan = zeta2(countforzeta, itemcount, theta, zetan);
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} else if ((itemcount < countforzeta) && (allowitemcountdecrease)) {
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zetan = zeta(itemcount, theta);
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}
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eta = (1 - pow(2.0 / items, 1 - theta)) / (1 - zeta2theta / zetan);
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u = rand_double();
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uz = u * zetan;
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if (uz < 1.0) {
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return base;
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}
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if (uz < 1.0 + pow(0.5, theta)) {
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return base + 1;
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}
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ret = base + (int)(itemcount * pow(eta * u - eta + 1, alpha));
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return ret;
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}
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int zipfian_next() {
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return next_int(items);
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}
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double zetastatic2(int st, int n, double theta, double initialsum) {
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int i;
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double sum = initialsum;
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for (i = st; i < n; i++) {
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sum += 1 / pow(i + 1, theta);
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}
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return sum;
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}
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double zeta2(int st, int n, double theta_val, double initialsum) {
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countforzeta = n;
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return zetastatic2(st, n, theta_val, initialsum);
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}
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double zetastatic(int n, double theta) {
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return zetastatic2(0, n, theta, 0);
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}
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double zeta(int n, double theta_val) {
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countforzeta = n;
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return zetastatic(n, theta_val);
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}
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void zipfian_generator4(int min, int max, double _zipfianconstant, double _zetan) {
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items = max - min + 1;
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base = min;
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zipfianconstant = _zipfianconstant;
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theta = zipfianconstant;
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zeta2theta = zeta(2, theta);
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alpha = 1.0 / (1.0 - theta);
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zetan = _zetan;
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countforzeta = items;
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eta = (1 - pow(2.0 / items, 1 - theta)) / (1 - zeta2theta / zetan);
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zipfian_next();
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}
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void zipfian_generator3(int min, int max, double zipfianconstant) {
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zipfian_generator4(min, max, zipfianconstant, zetastatic(max - min + 1, zipfianconstant));
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}
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void zipfian_generator2(int min, int max) {
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zipfian_generator3(min, max, ZIPFIAN_CONSTANT);
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}
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void zipfian_generator(int items) {
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zipfian_generator2(0, items - 1);
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}
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#if 0 /* test */
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void main() {
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int i = 0;
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int histogram[1000] = { 0 };
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srand(time(0));
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zipfian_generator(1000);
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for (i = 0; i < 1000000; i++) {
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int val = next_value();
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//printf("%d\n", val);
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histogram[val]++;
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}
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for (i = 0; i < 1000; i++) {
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printf("%d\n", histogram[i]);
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}
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}
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#endif
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