bsdgamesのprimesコマンドで素数を表示することができます。
| 準備するもの |
|
インストールはapt-get一発です。
# apt-get install bsdgames
では使ってみます。primesコマンドの引数に範囲を指定するか、
takk@deb83:~$ primes 2 20 2 3 5 7 11 13 17 19 takk@deb83:~$
開始する数字を指定すれば、素数が表示されます。
(開始の数字のみの場合はCTRL+Cするまで表示が止まりません)
takk@deb83:~$ primes 1000 1009 1013 1019 1021 1031 1033 1039 1049 1051 1061 (省略)
どんなアルゴリズムを使っているのでしょうか。ソースのコメントを読んでみます。
takk@deb83:~$ apt-get source bsdgames (省略) takk@deb83:~$ cd bsdgames-2.17/ takk@deb83:~/bsdgames-2.17$ cd primes takk@deb83:~/bsdgames-2.17/primes$
コメントは各行の2文字目にアスタリスクがあるようです。2番目にアスタリスクがある行をgrepで抽出します。
takk@deb83:~/bsdgames-2.17/primes$ grep '^.\*' primes.c | leafpad
/* $NetBSD: primes.c,v 1.19 2011/08/30 02:58:04 jakllsch Exp $ */
/*
* Copyright (c) 1989, 1993
* The Regents of the University of California. All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Landon Curt Noll.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
/*
* primes - generate a table of primes between two values
*
* By: Landon Curt Noll chongo@toad.com, ...!{sun,tolsoft}!hoptoad!chongo
*
* chongo <for a good prime call: 391581 * 2^216193 - 1> /\oo/\
*
* usage:
* primes [start [stop]]
*
* Print primes >= start and < stop. If stop is omitted,
* the value 4294967295 (2^32-1) is assumed. If start is
* omitted, start is read from standard input.
*
* validation check: there are 664579 primes between 0 and 10^7
*/
/*
* Eratosthenes sieve table
*
* We only sieve the odd numbers. The base of our sieve windows are always
* odd. If the base of table is 1, table[i] represents 2*i-1. After the
* sieve, table[i] == 1 if and only iff 2*i-1 is prime.
*
* We make TABSIZE large to reduce the overhead of inner loop setup.
*/
/*
* prime[i] is the (i-1)th prime.
*
* We are able to sieve 2^32-1 because this byte table yields all primes
* up to 65537 and 65537^2 > 2^32-1.
*/
/*
* To avoid excessive sieves for small factors, we use the table below to
* setup our sieve blocks. Each element represents a odd number starting
* with 1. All non-zero elements are factors of 3, 5, 7, 11 and 13.
*/
/*
* read_num_buf --
* This routine returns a number n, where 0 <= n && n <= BIG.
*/
/*
* primes - sieve and print primes from start up to and but not including stop
*
* start where to start generating
* stop don't generate at or above this value
*/
やはりエラトステネスの篩(Eratosthenes sieve)を使っているようですね。
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