用C语言思想改写的用筛法求质数程序(第2修订版)的一些源代码

// Decompiled by Jad v1.5.8e2. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://kpdus.tripod.com/jad.html
// Decompiler options: packimports(3)
// Source File Name:   Sieve.java

import java.io.PrintStream;

public class Sieve
{

    public Sieve()
    {
    }

    public static void main(String args[])
    {
        int i = 100;
        try
        {
            i = Integer.parseInt(args[0]);
        }
        catch(Exception exception) { }
        boolean aflag[] = new boolean[i + 1];
        for(int j = 0; j <= i; j++)
            aflag[j] = true;

        aflag[0] = aflag[1] = false;
        int k = (int)Math.ceil(Math.sqrt(i));
        for(int l = 0; l <= k; l++)
            if(aflag[l])
            {
                for(int i1 = 2 * l; i1 <= i; i1 += l)
                    aflag[i1] = false;

            }

        int j1;
        for(j1 = i; !aflag[j1]; j1--);
        System.out.println("The largest prime less than or equal to " + i + " is " + j1);
    }
}
// Decompiled by Jad v1.5.8e2. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://kpdus.tripod.com/jad.html
// Decompiler options: packimports(3)
// Source File Name:   Sieve2.java

import java.io.PrintStream;

public class Sieve2
{

    public Sieve2()
    {
    }

    public static void main(String args[])
    {
        int i = 100;
        try
        {
            i = Integer.parseInt(args[0]);
        }
        catch(Exception exception) { }
        int j = (i + 1) / 2;
        boolean aflag[] = new boolean[j + 1];
        int k = 0;
        for(int l = 0; l <= j; l++)
            aflag[l] = true;

        aflag[0] = false;
        aflag[1] = true;
        int i1 = (int)Math.ceil(Math.sqrt(i));
        for(int j1 = 3; j1 <= i1; j1 += 2)
            if(aflag[(j1 - 1) / 2])
            {
                for(int k1 = 3 * j1; k1 <= i; k1 = k1 + j1 + j1)
                    aflag[(k1 - 1) / 2] = false;

            }

        int l1 = 2;
        if(i <= 2)
            l1 = 2;
        else
        if(i % 2 == 1 && aflag[(i - 1) / 2])
            l1 = i;
        else
            for(l1 = i - 1 - i % 2; !aflag[(l1 - 1) / 2]; l1 -= 2);
        System.out.println("The largest prime less than or equal to " + i + " is " + l1 + " cycle time:" + k);
    }
}
// Decompiled by Jad v1.5.8e2. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://kpdus.tripod.com/jad.html
// Decompiler options: packimports(3)
// Source File Name:   Sieve3.java

import java.io.PrintStream;

public class Sieve3
{

    public Sieve3()
    {
    }

    public static void main(String args[])
    {
        int i = 100;
        try
        {
            i = Integer.parseInt(args[0]);
        }
        catch(Exception exception) { }
        int j = (i + 1) / 2;
        boolean aflag[] = new boolean[j + 1];
        int k = 0;
        for(int l = 0; l <= j; l++)
            aflag[l] = true;

        aflag[0] = false;
        aflag[1] = true;
        int i1 = (int)Math.ceil(Math.sqrt(i));
        for(int j1 = 3; j1 <= i1; j1 += 2)
            if(aflag[(j1 - 1) / 2])
            {
                for(int k1 = j1 * j1; k1 <= i; k1 = k1 + j1 + j1)
                {
                    int i2 = (k1 - 1) / 2;
                    if(aflag[i2])
                        aflag[i2] = false;
                }

            }

        int l1 = 2;
        if(i <= 2)
            l1 = 2;
        else
        if(i % 2 == 1 && aflag[(i - 1) / 2])
            l1 = i;
        else
            for(l1 = i - 1 - i % 2; !aflag[(l1 - 1) / 2]; l1 -= 2);
        System.out.println("The largest prime less than or equal to " + i + " is " + l1 + " cycle time:" + k);
    }
}
// Decompiled by Jad v1.5.8e2. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://kpdus.tripod.com/jad.html
// Decompiler options: packimports(3)
// Source File Name:   Sieve4.java

import java.io.PrintStream;

public class Sieve4
{

    public Sieve4()
    {
    }

    public static void main(String args[])
    {
        int i = 100;
        try
        {
            i = Integer.parseInt(args[0]);
        }
        catch(Exception exception) { }
        int j = (i + 1) / 2;
        long l = System.currentTimeMillis();
        boolean aflag[] = new boolean[j + 1];
        int k = 0;
        aflag[0] = false;
        aflag[1] = true;
        int i1 = (int)Math.ceil(Math.sqrt(i));
        int j1 = (i - 1) / 2 - 1;
        for(int l1 = 2; l1 <= j1;)
        {
            aflag[l1++] = true;
            aflag[l1++] = true;
            aflag[l1++] = false;
        }

        long l2 = System.currentTimeMillis() - l;
        System.out.println(l2);
        int j2 = (i1 - 1) / 2;
        int k2 = (i - 1) / 2;
        for(int k1 = 2; k1 <= j2; k1++)
            if(aflag[k1])
            {
                for(int i2 = k1 * (2 * k1 + 2); i2 <= k2; i2 = i2 + k1 + k1 + 1)
                    if(aflag[i2])
                        aflag[i2] = false;

            }

        int i3 = 2;
        if(i <= 2)
            i3 = 2;
        else
        if(i % 2 == 1 && aflag[(i - 1) / 2])
            i3 = i;
        else
            for(i3 = i - 1 - i % 2; !aflag[(i3 - 1) / 2]; i3 -= 2);
        long l3 = System.currentTimeMillis() - l;
        System.out.println(l3);
        System.out.println("The largest prime less than or equal to " + i + " is " + i3 + " cycle time:" + k);
    }
}
// Decompiled by Jad v1.5.8e2. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://kpdus.tripod.com/jad.html
// Decompiler options: packimports(3)
// Source File Name:   Sieve5.java

import java.io.PrintStream;

public class Sieve5
{

    public Sieve5()
    {
    }

    public static int getisp(int i)
    {
        return isprime[i >> 3] >> (i & 7) & 1;
    }

    public static void main(String args[])
    {
        int i = 100;
        try
        {
            i = Integer.parseInt(args[0]);
        }
        catch(Exception exception) { }
        int j = (i + 1) / 2;
        isprime = new byte[j / 8 + 2];
        int k = 0;
        for(int l = 0; l <= j / 8 + 1; l++)
            isprime[l] = -1;

        isprime[0] &= 0xfe;
        isprime[0] |= 2;
        int k1 = (int)Math.ceil(Math.sqrt(i));
        boolean flag = false;
        int i1 = (i - 1) / 2;
        for(int i2 = 4; i2 <= i1; i2 += 3)
            isprime[i2 >> 3] &= ~(1 <<(i2 & 7));

        char c = '/0';
        int j2 = (k1 - 1) / 2;
        int k2 = (i - 1) / 2;
        for(int j1 = 2; j1 <= j2; j1++)
        {
            c++;
            if(c == '/003')
                c = '/0';
            else
            if(getisp(j1) == 1)
            {
                int l1 = ((j1 <<2) + 1) % 3;
                for(int l2 = j1 * (2 * j1 + 2); l2 <= k2; l2 = l2 + j1 + j1 + 1)
                    if(++l1 == 3)
                        l1 = 0;
                    else
                    if(getisp(l2) == 1)
                        isprime[l2 >> 3] &= ~(1 <<(l2 & 7));

            }
        }

        int i3 = 2;
        if(i <= 2)
            i3 = 2;
        else
        if(i % 2 == 1 && getisp((i - 1) / 2) == 1)
        {
            i3 = i;
        } else
        {
            i3 = i - 1 - i % 2;
            do
            {
                int j3 = (i3 - 1) / 2;
                if(getisp(j3) == 1)
                    break;
                i3 -= 2;
            } while(true);
        }
        System.out.println("The largest prime less than or equal to " + i + " is " + i3 + " cycle time:" + k);
    }

    static byte isprime[];
}
// Decompiled by Jad v1.5.8f. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://www.kpdus.com/jad.html
// Decompiler options: packimports(3)
// Source File Name:   Sieve7.java

import java.io.PrintStream;

public class Sieve7
{

    public Sieve7()
    {
    }

    public static int getisp(int i)
    {
        return isprime[i >> 3] >> (i & 7) & 1;
    }

    public static void main(String args[])
    {
        int i = 100;
        try
        {
            i = Integer.parseInt(args[0]);
        }
        catch(Exception exception) { }
        int j = (i + 1) / 2;
        isprime = new byte[((j / 8) * 2) / 3 + 2];
        int k = 0;
        for(int l = 0; l <= ((j / 8) * 2) / 3 + 1; l++)
            isprime[l] = -1;

        isprime[0] &= 0xfe;
        isprime[0] |= 2;
        int l1 = (int)Math.ceil(Math.sqrt(i));
        boolean flag = false;
        int i1 = (i - 1) / 2;
        char c = '/0';
        for(int j1 = 5; j1 <= l1; j1 += 2)
        {
            c++;
            if(c == '/003')
            {
                c = '/0';
            } else
            {
                int j2 = j1 / 3;
                if(getisp(j2) == 1)
                {
                    int i2 = (j1 + j1) % 3 - 1;
                    for(int l2 = j1 * j1; l2 <= i; l2 = l2 + j1 + j1)
                        if(++i2 == 3)
                        {
                            i2 = 0;
                        } else
                        {
                            int i3 = l2 / 3;
                            if(getisp(i3) == 1)
                                isprime[i3 >> 3] &= ~(1 <<(i3 & 7));
                        }

                }
            }
        }

        int k2 = 2;
        if(i <= 2)
            k2 = 2;
        else
        if(i <= 4)
            k2 = 3;
        else
        if(i % 2 == 1 && getisp(i / 3) == 1)
        {
            k2 = i;
        } else
        {
            for(int k1 = (j * 2) / 3; k1 >= 0; k1--)
            {
                if(getisp(k1) != 1)
                    continue;
                k2 = 3 * k1 + k1 % 2 + 1;
                if(k2                     break;
            }

        }
        System.out.println("The largest prime less than or equal to " + i + " is " + k2 + " cycle time:" + k);
    }

    static byte isprime[];
}