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/* Finding the next prime >= a given small integer.
Copyright (C) 1995-2025 Free Software Foundation, Inc.
This file is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation; either version 2.1 of the
License, or (at your option) any later version.
This file 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 Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
#include <config.h>
/* Specification. */
#include "next-prime.h"
#include <stdint.h> /* for SIZE_MAX */
/* Return true if CANDIDATE is a prime number or 1.
CANDIDATE should be an odd number >= 1. */
static bool _GL_ATTRIBUTE_CONST
is_prime (size_t candidate)
{
size_t divisor = 3;
size_t square = divisor * divisor;
for (;;)
{
if (square > candidate)
return true;
if ((candidate % divisor) == 0)
return false;
/* Increment divisor by 2. */
divisor++;
square += 4 * divisor;
divisor++;
}
}
size_t _GL_ATTRIBUTE_CONST
next_prime (size_t candidate)
{
#if !defined IN_LIBGETTEXTLIB
/* Skip small primes. */
if (candidate < 10)
candidate = 10;
#endif
/* Make it definitely odd. */
candidate |= 1;
while (SIZE_MAX != candidate && !is_prime (candidate))
candidate += 2;
return candidate;
}
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