从Perl到Java

use strict;
use warnings;

my $magic = <number>;

sub largestprimef($);
sub max($$);

print largestprimef($magic);

sub largestprimef($) {
    my $n = shift;

    my $i;
    return largestprimef(max(2,$n/2)) if($n % 2 == 0); 
    my $sn = int( sqrt($n) );

    for ( $i = 3 ; $i <= $sn ; $i += 2 ) {
        if ( $n % $i == 0 ) { last; }
    }
    if ( $i > $sn )    #loop ran over,means the number is prime
    {
        return $n;
    }
    else {
        return max( $i,largestprimef( $n / $i ) );
    }
}

sub max($$) {
    return ( sort { $a <=> $b } (@_) )[1];
}

现在该算法似乎有效！ Perl的一个小问题是它不接受真正的大数字.所以我改写了

my $magic = <number>;

至

my $magic = Math::BigInt->new(' <number> ');

但这只是运行了很多年龄.所以我把它重写为Java(我更熟悉),这导致了这个：

static final BigInteger two = new BigInteger( "2" );

public static void main( String[] args ) {
    BigInteger number = new BigInteger( "<number>" );

    System.out.println( goAtIt( number ) );
}

static BigInteger goAtIt( BigInteger prime ) {
    if ( isEven( prime ) )
        return goAtIt( prime.divide( two ).max( two ) );

    BigInteger sqrt = sqrt( prime );
    BigInteger comp = new BigInteger( "3" );

    while (sqrt.compareTo( comp ) > 0) {
        if ( prime.remainder( comp ).equals( BigInteger.ZERO ) )
            break;
        comp = comp.add( two );
    }

    if ( comp.compareTo( sqrt ) > 0 )
        return prime;

    return comp.max( goAtIt( prime.divide( comp ) ) );
}

作为辅助设备(看起来很好)：

static boolean isEven( BigInteger number ) {
    return number.getLowestSetBit() != 0;
}

static BigInteger sqrt( BigInteger n ) {
    BigInteger a = BigInteger.ONE;
    BigInteger b = new BigInteger( n.shiftRight( 5 ).add( new BigInteger( "8" ) ).toString() );
    while (b.compareTo( a ) >= 0) {
        BigInteger mid = new BigInteger( a.add( b ).shiftRight( 1 ).toString() );
        if ( mid.multiply( mid ).compareTo( n ) > 0 )
            b = mid.subtract( BigInteger.ONE );
        else
            a = mid.add( BigInteger.ONE );
    }
    return a.subtract( BigInteger.ONE );
}

但是我的结果总是关闭……而且我的Perl对原始代码进行逆向工程并不是那么好.有没有人知道我错过了什么？

==更新：问题(某种程度上)通过解决方法解决