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htable: use precalculated list of primes #3739

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May 31, 2023
Merged

htable: use precalculated list of primes #3739

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htable: use precalculated list of primes
dtikhonov May 30, 2023
f0bfcb2
Test htable growth
dtikhonov May 30, 2023
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25 changes: 13 additions & 12 deletions main/htable.c
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Original file line number Diff line number Diff line change
Expand Up @@ -258,24 +258,25 @@ static void hashTablePutItem00 (hashTable *htable, void *key, void *val
htable->count++;
}

/* TODO: A pre-calculated array can be used instead of
* finding a new one at runtume. */
/* "doubling" primes smaller than 2^32 */
static const unsigned int primes[] = {
3, 7, 17, 37, 79, 163, 331, 673, 1361, 2729, 5471, 10949, 21911,
43853, 87719, 175447, 350899, 701819, 1403641, 2807303, 5614657,
11229331, 22458671, 44917381, 89834777, 179669557, 359339171,
718678369, 1437356741, 2874713497,
};

static unsigned int
prime_double(unsigned int i)
{
unsigned int j;

Assert (i > 2);
Assert (i % 2);

for (unsigned int c = 2 * i + 1; ; c += 2)
{
for (unsigned int i0 = 3; i0 < i; i0 += 2)
{
if ((c % i0) == 0)
goto next;
}
return c;
next:;
}
for (j = 0; j < sizeof(primes) / sizeof(primes[0]); ++j)
if (primes[j] > i)
return primes[j];

return i;
}
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