Added a table of prime numbers. (I want to use prime numbers for hash table

sizes, but since the hash tables will be short-lived, I don't want to spend
much time by calculating primes.)

diff --git a/lib/Makefile b/lib/Makefile
index 73501c7b55a80c791881fb4959ada6c0e07510de..c785ee643274a55be247c61fbd7f62b089a361cb 100644 (file)
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -1,4 +1,4 @@
-# Makefile for the UCW Library (c) 1997--2004 Martin Mares <mj@ucw.cz>
+# Makefile for the UCW Library (c) 1997--2005 Martin Mares <mj@ucw.cz>
 
 DIRS+=lib
 
@@ -17,7 +17,7 @@ LIBUCW_MODS= \
        fb-file carefulio fb-mem fb-temp fb-mmap fb-limfd fb-buffer \
        str_ctype str_upper str_lower unicode-utf8 stkstring \
        wildmatch wordsplit ctmatch patimatch patmatch regex \
-       prime random timer randomkey \
+       prime primetable random timer randomkey \
        bit-ffs bit-fls \
        db \
        url \

diff --git a/lib/lib.h b/lib/lib.h
index df728fdb5099cc29049239efbe55397a9b11d2ce..a1e2b79238c86c2c8cce1779480179518d58a853 100644 (file)
--- a/lib/lib.h
+++ b/lib/lib.h
@@ -168,6 +168,11 @@ void hex_to_md5(byte *, byte *);
 int isprime(uns);
 uns nextprime(uns);
 
+/* primetable.c */
+
+uns next_table_prime(uns x);
+uns prev_table_prime(uns x);
+
 /* timer.c */
 
 struct timeval;

diff --git a/lib/primetable.c b/lib/primetable.c
new file mode 100644 (file)
index 0000000..2e6fe5d
--- /dev/null
+++ b/lib/primetable.c
@@ -0,0 +1,164 @@
+/*
+ *     UCW Library -- Prime Number Table
+ *
+ *     (c) 2005 Martin Mares <mj@ucw.cz>
+ *
+ *     This software may be freely distributed and used according to the terms
+ *     of the GNU Lesser General Public License.
+ */
+
+#include "lib/lib.h"
+#include "lib/binsearch.h"
+
+/* A table of odd primes, each is about 1.2 times the previous one */
+static uns prime_table[] = {
+  3,
+  7,
+  13,
+  19,
+  29,
+  37,
+  53,
+  67,
+  89,
+  109,
+  137,
+  173,
+  211,
+  263,
+  331,
+  409,
+  499,
+  601,
+  727,
+  877,
+  1061,
+  1279,
+  1543,
+  1861,
+  2239,
+  2689,
+  3229,
+  3877,
+  4657,
+  5623,
+  6761,
+  8123,
+  9767,
+  11731,
+  14083,
+  16903,
+  20287,
+  24359,
+  29243,
+  35099,
+  42131,
+  50581,
+  60703,
+  72859,
+  87433,
+  104933,
+  125927,
+  151121,
+  181361,
+  217643,
+  261223,
+  313471,
+  376171,
+  451411,
+  541699,
+  650059,
+  780119,
+  936151,
+  1123391,
+  1348111,
+  1617739,
+  1941293,
+  2329559,
+  2795477,
+  3354581,
+  4025507,
+  4830619,
+  5796797,
+  6956203,
+  8347483,
+  10017011,
+  12020431,
+  14424539,
+  17309471,
+  20771371,
+  24925661,
+  29910821,
+  35892991,
+  43071601,
+  51685939,
+  62023139,
+  74427803,
+  89313379,
+  107176057,
+  128611313,
+  154333591,
+  185200339,
+  222240413,
+  266688509,
+  320026249,
+  384031507,
+  460837813,
+  553005391,
+  663606499,
+  796327811,
+  955593439,
+  1146712139,
+  1376054569,
+  1651265507,
+  1981518631,
+  2377822387,
+  2853386881,
+  3424064269,
+  4108877153,
+  4294967291
+};
+
+#define NPRIMES ARRAY_SIZE(prime_table)
+
+uns
+next_table_prime(uns x)
+{
+  if (x >= prime_table[NPRIMES-1])
+    return 0;
+  else
+    return prime_table[BIN_SEARCH_FIRST_GE(prime_table, NPRIMES, x+1)];
+}
+
+uns
+prev_table_prime(uns x)
+{
+  int i = BIN_SEARCH_FIRST_GE(prime_table, NPRIMES, x);
+  return i ? prime_table[i-1] : 0;
+}
+
+#ifdef TEST
+
+#include <stdio.h>
+
+int main(void)
+{
+#if 0          /* Generate the table */
+  uns x = 3, xx;
+  do
+    {
+      printf("  %u,\n", x);
+      xx = x;
+      x = nextprime(1.2*x);
+    }
+  while (x > xx);
+#else
+  for (int i=1; i<=100; i++)
+    printf("%d\t%d\t%d\n", i, next_table_prime(i), prev_table_prime(i));
+  for (uns i=0xfffffff0; i; i++)
+    printf("%u\t%u\t%u\n", i, next_table_prime(i), prev_table_prime(i));
+  return 0;
+#endif
+}
+
+#endif