OpenEuphoria: Euphoria v4.1

# OpenEuphoria Manual

## Euphoria v4.1

routine or constant name search

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## 8.30 Prime Numbers

### 8.30.1 Routines

#### 8.30.1.1 calc_primes

    include std/primes.e
    namespace primes
    public function calc_primes(integer approx_limit, atom time_limit_p = 10)

returns all the prime numbers below a threshold, with a cap on computation time.

##### Parameters:

1. `approx_limit` : an integer, This is not the upper limit but the last prime returned is the next prime after or on this value.
2. `time_out_p` : an atom, the maximum number of seconds that this function can run for. The default is 10 (ten) seconds.

##### Returns:

A sequence, made of prime numbers in increasing order. The last value is the next prime number that falls on or after the value of `approx_limit`.

##### Comments:

- The `approx_limit` argument does not represent the largest value to return. The largest value returned will be the next prime number on or after
- The returned sequence contains all the prime numbers less than its last element.

- If the function times out, it may not hold all primes below `approx_limit`, but only the largest ones will be absent. If the last element returned is less than `approx_limit` then the function timed out.

- To disable the timeout, simply give it a negative value.

##### Example 1:

    ? calc_primes(1000, 5)
    -- On a very slow computer, you may only get all primes up to say 719.
    -- On a faster computer, the last element printed out will be 1009.
    -- This call will never take longer than 5 seconds.

##### See Also:

next_prime prime_list

#### 8.30.1.2 next_prime

    include std/primes.e
    namespace primes
    public function next_prime(integer n, object fail_signal_p = - 1, atom time_out_p = 1)

returns the next prime number on or after the supplied number.

##### Parameters:

1. `n` : an integer, the starting point for the search
2. `fail_signal_p` : an integer, used to signal error. Defaults to -1.

##### Returns:

An integer, which is prime only if it took less than one second to determine the next prime greater or equal to `n`.

##### Comments:

The default value of -1 will alert you about an invalid returned value, since a prime not less than `n` is expected. However, you can pass another value for this parameter.

##### Example 1:

    ? next_prime(997)
    -- On a very slow computer, you might get -997, but 1009 is expected.

##### See Also:

calc_primes

#### 8.30.1.3 prime_list

    include std/primes.e
    namespace primes
    public function prime_list(integer top_prime_p = 0)

returns a list of prime numbers.

##### Parameters:

1. `top_prime_p` : The list will end with the prime less than or equal to this value. If `top_prime_p` is zero, the current list of calculated primes is returned.

##### Returns:

An sequence, a list of prime numbers from `2` to `<=` `top_prime_p`

##### Example 1:

    sequence pList = prime_list(1000)
    -- pList will now contain all the primes from 2 up to the largest less than or
    --    equal to 1000, which is 997.

##### See Also:

calc_primes, next_prime

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