factor: prepare for the new factor program

* src/make-prime-list.c: New file, from nt-factor.
Co-authored-by: Niels Möller <nisse@lysator.liu.se>

diff --git a/src/make-prime-list.c b/src/make-prime-list.c
new file mode 100644 (file)
index 0000000..1f5b3ce
--- /dev/null
+++ b/src/make-prime-list.c
@@ -0,0 +1,168 @@
+/* Factoring of uintmax_t numbers. Generation of needed tables.
+
+   Contributed to the GNU project by Torbjörn Granlund and Niels Möller
+   Contains code from GNU MP.
+
+Copyright 2012 Free Software Foundation, Inc.
+
+This program is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free Software
+Foundation; either version 3 of the License, or (at your option) any later
+version.
+
+This program is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License along with
+this program.  If not, see http://www.gnu.org/licenses/.  */
+
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+struct prime
+{
+  unsigned p;
+  uintmax_t pinv; /* Inverse mod b = 2^{bitsize of uintmax_t} */
+  uintmax_t lim; /* floor(UINTMAX_MAX / p) */
+};
+
+static uintmax_t
+binvert (uintmax_t a)
+{
+  uintmax_t x = 0xf5397db1 >> (4*((a/2) & 0x7));
+  for (;;)
+    {
+      uintmax_t y = 2*x - x*x*a;
+      if (y == x)
+        return x;
+      x = y;
+    }
+}
+
+static void
+process_prime (struct prime *info, unsigned p)
+{
+  info->p = p;
+  info->pinv = binvert (p);
+  info->lim = UINTMAX_MAX / (uintmax_t) p;
+}
+
+static void
+output_primes (const struct prime *primes, unsigned nprimes)
+{
+  unsigned i;
+  unsigned p;
+  int is_prime;
+  const char *suffix;
+
+  puts ("/* Generated file -- DO NOT EDIT */\n");
+
+  if (sizeof(uintmax_t) <= sizeof(unsigned long))
+    suffix = "UL";
+  else if (sizeof(uintmax_t) <= sizeof(unsigned long long))
+    suffix = "ULL";
+  else
+    {
+      fprintf (stderr, "Don't know how to write uintmax_t constants.\n");
+      exit (EXIT_FAILURE);
+    }
+
+#define SZ (int)(2*sizeof(uintmax_t))
+
+  for (i = 0, p = 2; i < nprimes; i++)
+    {
+      printf ("P(%2u, %3u, 0x%0*jx%s, 0x%0*jx%s) /* %d */\n",
+              primes[i].p - p,
+              (i + 8 < nprimes) ? primes[i + 8].p - primes[i].p : 0xff,
+              SZ, primes[i].pinv, suffix,
+              SZ, primes[i].lim, suffix, primes[i].p);
+      p = primes[i].p;
+    }
+
+  printf ("\n#undef FIRST_OMITTED_PRIME\n");
+
+  /* Find next prime */
+  do
+    {
+      p += 2;
+      for (i = 0, is_prime = 1; is_prime; i++)
+        {
+          if (primes[i].p * primes[i].p > p)
+            break;
+          if ( (uintmax_t) p * primes[i].pinv <= primes[i].lim)
+            {
+              is_prime = 0;
+              break;
+            }
+        }
+    }
+  while (!is_prime);
+
+  printf ("#define FIRST_OMITTED_PRIME %d\n", p);
+}
+
+static void *
+xalloc (size_t s)
+{
+  void *p = malloc(s);
+  if (p)
+    return p;
+
+  fprintf (stderr, "Virtual memory exhausted.\n");
+  exit (EXIT_FAILURE);
+}
+
+int
+main (int argc, char **argv)
+{
+  int limit;
+
+  char *sieve;
+  size_t size, i;
+
+  struct prime *prime_list;
+  unsigned nprimes;
+
+  if (argc != 2)
+    {
+      fprintf (stderr, "Usage: %s LIMIT\n"
+               "Produces a list of odd primes <= LIMIT\n", argv[0]);
+      return EXIT_FAILURE;
+    }
+  limit = atoi(argv[1]);
+  if (limit < 3)
+    exit (EXIT_SUCCESS);
+
+  /* Make limit odd */
+  if ( !(limit & 1))
+    limit--;
+
+  size = (limit-1)/2;
+  /* sieve[i] represents 3+2*i */
+  sieve = xalloc (size);
+  memset (sieve, 1, size);
+
+  prime_list = xalloc (size * sizeof (*prime_list));
+  nprimes = 0;
+
+  for (i = 0; i < size;)
+    {
+      unsigned p = 3+2*i;
+      unsigned j;
+
+      process_prime (&prime_list[nprimes++], p);
+
+      for (j = (p*p - 3)/2; j < size; j+= p)
+        sieve[j] = 0;
+
+      while (i < size && sieve[++i] == 0)
+        ;
+    }
+
+  output_primes (prime_list, nprimes);
+
+  return EXIT_SUCCESS;
+}