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166 lines
2.2 KiB
166 lines
2.2 KiB
3 months ago
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/*
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* UCW Library -- Prime Number Table
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*
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* (c) 2005 Martin Mares <mj@ucw.cz>
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*
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* This software may be freely distributed and used according to the terms
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* of the GNU Lesser General Public License.
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*/
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#include <ucw/lib.h>
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#include <ucw/prime.h>
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#include <ucw/binsearch.h>
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/* A table of odd primes, each is about 1.2 times the previous one */
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static uint prime_table[] = {
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3,
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7,
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13,
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19,
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29,
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37,
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53,
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67,
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89,
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109,
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137,
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173,
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211,
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263,
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331,
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409,
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499,
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601,
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727,
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877,
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1061,
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1279,
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1543,
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1861,
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2239,
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2689,
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3229,
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3877,
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4657,
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5623,
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6761,
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8123,
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9767,
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11731,
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14083,
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16903,
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20287,
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24359,
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29243,
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35099,
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42131,
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50581,
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60703,
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72859,
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87433,
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104933,
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125927,
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151121,
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181361,
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217643,
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261223,
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313471,
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376171,
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451411,
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541699,
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650059,
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780119,
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936151,
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1123391,
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1348111,
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1617739,
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1941293,
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2329559,
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2795477,
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3354581,
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4025507,
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4830619,
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5796797,
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6956203,
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8347483,
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10017011,
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12020431,
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14424539,
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17309471,
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20771371,
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24925661,
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29910821,
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35892991,
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43071601,
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51685939,
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62023139,
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74427803,
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89313379,
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107176057,
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128611313,
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154333591,
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185200339,
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222240413,
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266688509,
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320026249,
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384031507,
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460837813,
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553005391,
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663606499,
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796327811,
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955593439,
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1146712139,
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1376054569,
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1651265507,
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1981518631,
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2377822387,
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2853386881,
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3424064269,
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4108877153,
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4294967291
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};
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#define NPRIMES ARRAY_SIZE(prime_table)
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uint
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next_table_prime(uint x)
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{
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if (x >= prime_table[NPRIMES-1])
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return 0;
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else
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return prime_table[BIN_SEARCH_FIRST_GE(prime_table, NPRIMES, x+1)];
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}
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uint
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prev_table_prime(uint x)
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{
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int i = BIN_SEARCH_FIRST_GE(prime_table, NPRIMES, x);
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return i ? prime_table[i-1] : 0;
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}
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#ifdef TEST
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#include <stdio.h>
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int main(void)
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{
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#if 0 /* Generate the table */
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uint x = 3, xx;
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do
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{
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printf(" %u,\n", x);
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xx = x;
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x = nextprime(1.2*x);
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}
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while (x > xx);
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#else
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for (int i=1; i<=100; i++)
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printf("%d\t%d\t%d\n", i, next_table_prime(i), prev_table_prime(i));
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for (uint i=0xfffffff0; i; i++)
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printf("%u\t%u\t%u\n", i, next_table_prime(i), prev_table_prime(i));
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return 0;
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#endif
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}
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#endif
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