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* hashtab.c (higher_prime_number): Use a table, rather than a

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seive, to find the next prime.
This commit is contained in:
DJ Delorie 2000-11-29 19:19:10 +00:00
parent 2ea7befd8e
commit 5ca0f83d75
2 changed files with 59 additions and 20 deletions
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5
libiberty/ChangeLog
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@ -1,3 +1,8 @@
2000-11-29 Mark Mitchell <mark@codesourcery.com>
* hashtab.c (higher_prime_number): Use a table, rather than a
seive, to find the next prime.
2000-11-29 Zack Weinberg <zack@wolery.stanford.edu> 2000-11-29 Zack Weinberg <zack@wolery.stanford.edu>
* aclocal.m4 (LIB_AC_PROG_CC): Moved here from configure.in. * aclocal.m4 (LIB_AC_PROG_CC): Moved here from configure.in.

74
libiberty/hashtab.c
View File

@ -71,35 +71,69 @@ static PTR *find_empty_slot_for_expand PARAMS ((htab_t, hashval_t));
htab_hash htab_hash_pointer = hash_pointer; htab_hash htab_hash_pointer = hash_pointer;
htab_eq htab_eq_pointer = eq_pointer; htab_eq htab_eq_pointer = eq_pointer;
/* The following function returns the nearest prime number which is /* The following function returns a nearest prime number which is
greater than a given source number, N. */ greater than N, and near a power of two. */
static unsigned long static unsigned long
higher_prime_number (n) higher_prime_number (n)
unsigned long n; unsigned long n;
{ {
unsigned long i; /* These are primes that are near, but slightly smaller than, a
power of two. */
static unsigned long primes[] = {
2,
7,
13,
31,
61,
127,
251,
509,
1021,
2039,
4093,
8191,
16381,
32749,
65521,
131071,
262139,
524287,
1048573,
2097143,
4194301,
8388593,
16777213,
33554393,
67108859,
134217689,
268435399,
536870909,
1073741789,
2147483647,
4294967291
};
/* Ensure we have a larger number and then force to odd. */ unsigned long* low = &primes[0];
n++; unsigned long* high = &primes[sizeof(primes) / sizeof(primes[0])];
n |= 0x01;
/* All odd numbers < 9 are prime. */ while (low != high)
if (n < 9) {
return n; unsigned long* mid = low + (high - low) / 2;
if (n > *mid)
low = mid + 1;
else
high = mid;
}
/* Otherwise find the next prime using a sieve. */ /* If we've run out of primes, abort. */
if (n > *low)
{
fprintf (stderr, "Cannot find prime bigger than %lu\n", n);
abort ();
}
next: return *low;
for (i = 3; i * i <= n; i += 2)
if (n % i == 0)
{
n += 2;
goto next;
}
return n;
} }
/* Returns a hash code for P. */ /* Returns a hash code for P. */