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hashtab.c (higher_prime_number): Use a table, rather than a seive, to find the next prime.

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* hashtab.c (higher_prime_number): Use a table, rather than a
	seive, to find the next prime.

From-SVN: r37775
This commit is contained in:
Mark Mitchell 2000-11-27 04:23:38 +00:00 committed by Mark Mitchell
parent e9608fe6f0
commit a4c9b97e26
2 changed files with 59 additions and 20 deletions
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5
libiberty/ChangeLog
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@ -1,3 +1,8 @@
2000-11-26 Mark Mitchell <mark@codesourcery.com>
* hashtab.c (higher_prime_number): Use a table, rather than a
seive, to find the next prime.
2000-11-22 H.J. Lu <hjl@gnu.org>
* cplus-dem.c (main): Handle gnat_demangling.

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_eq htab_eq_pointer = eq_pointer;
/* The following function returns the nearest prime number which is
greater than a given source number, N. */
/* The following function returns a nearest prime number which is
greater than N, and near a power of two. */
static unsigned long
higher_prime_number (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. */
n++;
n |= 0x01;
unsigned long* low = &primes[0];
unsigned long* high = &primes[sizeof(primes) / sizeof(primes[0])];
/* All odd numbers < 9 are prime. */
if (n < 9)
return n;
while (low != high)
{
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:
for (i = 3; i * i <= n; i += 2)
if (n % i == 0)
{
n += 2;
goto next;
}
return n;
return *low;
}
/* Returns a hash code for P. */