java 16進数文字列とdouble型の相互変換

学校の課題で作ったので置いておく
他の言語にも応用できる(無理矢理やったのでもっといい方法はあるきがする)

16進数文字列からdoubleへの変換

MyDouble.java

    //bitのたってるところと何桁目かで値を計算
    private static double bitToDouble(final int bit,final int digit)
    {
        return bit*Math.pow(2, digit);
    }

    //4bitまとめて計算
    private static double bit4ToDouble(final int bit1,final int bit2,final int bit3,final int bit4, final int digit)
    {
        final int bit1Dig=digit*4;
        return bitToDouble(bit1,bit1Dig+3)+bitToDouble(bit2,bit1Dig+2)+bitToDouble(bit3,bit1Dig+1)+bitToDouble(bit4,bit1Dig);
    }
    //16進数文字と桁数から値を計算
    private static double hexCharToDouble(final char c, final int digit)
    {

        switch(c)
        {
        case '0':return bit4ToDouble(0,0,0,0,digit);
        case '1':return bit4ToDouble(0,0,0,1,digit);
        case '2':return bit4ToDouble(0,0,1,0,digit);
        case '3':return bit4ToDouble(0,0,1,1,digit);
        case '4':return bit4ToDouble(0,1,0,0,digit);
        case '5':return bit4ToDouble(0,1,0,1,digit);
        case '6':return bit4ToDouble(0,1,1,0,digit);
        case '7':return bit4ToDouble(0,1,1,1,digit);
        case '8':return bit4ToDouble(1,0,0,0,digit);
        case '9':return bit4ToDouble(1,0,0,1,digit);
        case 'a':
        case 'A':return bit4ToDouble(1,0,1,0,digit);
        case 'b':
        case 'B':return bit4ToDouble(1,0,1,1,digit);
        case 'c':
        case 'C':return bit4ToDouble(1,1,0,0,digit);
        case 'd':       
        case 'D':return bit4ToDouble(1,1,0,1,digit);
        case 'e':
        case 'E':return bit4ToDouble(1,1,1,0,digit);
        case 'f':
        case 'F':return bit4ToDouble(1,1,1,1,digit);
        }
        return 0;
    }


    //16進数文字列から値を計算
    public static double hexStringToDouble(final String str)
    {
        double result=0;

        boolean minus=str.charAt(0)=='-';
        int dot=str.indexOf('.');

        for(int i=0;i<str.length();++i)
        {
            if(i==dot)
                continue;
            char c=str.charAt(i);
            int dig;
            if(dot==-1)
                dig=str.length()-i-1;
            else
            {
                dig=dot-i;
                if(i<dot)
                    dig-=1;
            }


            result+=hexCharToDouble(c,dig);
        }
        return minus?-result:result;
    }

doubleから16進数文字列への変換

MyDouble.java

    //整数部分
    private static String I(int num)
    {
        String bit="";

        if(num==0)
            return "0";
        while(num>0)
        {

            bit+=Integer.toString(num%2);
            num/=2;
        }
        StringBuffer buf= new StringBuffer(bit);
        bit=buf.reverse().toString();

        return bit;
    }
    //少数部分
    private static String D(double num)
    {
        String bit="";

        if(num==0)
            return "0";
        while((0-num)!=0)
        {
            num*=2;
            bit+=(int)num;

            num-=(int)num;
        }
        StringBuffer buf= new StringBuffer(bit);
        bit=buf.reverse().toString();

        return bit;
    }
    //値から4bit分の数値取得
    private static int charToBit4(char b1,char b2,char b3,char b4)
    {
        return (int)(b1-48)*1000+(int)(b2-48)*100+(int)(b3-48)*10+(int)(b4-48);
    }
    //4bit分数値から16進数文字取得
    private static String bit4IntToHex(int bit4)
    {
        switch(bit4)
        {
        case 0:return "0";
        case 1:return "1";
        case 10:return "2";
        case 11:return "3";
        case 100:return "4";
        case 101:return "5";
        case 110:return "6";
        case 111:return "7";
        case 1000:return "8";
        case 1001:return "9";
        case 1010:return "A";
        case 1011:return "B";
        case 1100:return "C";
        case 1101:return "D";
        case 1110:return "E";
        case 1111:return "F";
        }
        return "";
    }

    //数値から16進数文字列取得
    static String doubleToHexString(double num)
    {
        boolean minus=num<0;
        num=Math.abs(num);
        String intbit=I((int)num);
        String intHex="";
        {       
            int numBitTable=(intbit.length()-1)/4+1;
            for(int i=intbit.length()-numBitTable*4,j=0;j<numBitTable;i+=4,++j)
            {
                char c1=i>=0?intbit.charAt(i):'0';
                char c2=i+1>=0?intbit.charAt(i+1):'0';
                char c3=i+2>=0?intbit.charAt(i+2):'0';
                char c4=i+3>=0?intbit.charAt(i+3):'0';
                int bit4=charToBit4(c1,c2,c3,c4);
                intHex+=bit4IntToHex(bit4);
            }

        }
        String dbit=D(num-(int)(num));
        String dHex="";
        {       
            int numBitTable=(dbit.length()-1)/4+1;
            for(int i=0,j=0;j<numBitTable;i+=4,++j)
            {
                char c1=i<dbit.length()?dbit.charAt(i):'0';
                char c2=i+1<dbit.length()?dbit.charAt(i+1):'0';
                char c3=i+2<dbit.length()?dbit.charAt(i+2):'0';
                char c4=i+3<dbit.length()?dbit.charAt(i+3):'0';
                int bit4=charToBit4(c1,c2,c3,c4);
                dHex+=bit4IntToHex(bit4);
            }

        }
        if(dHex.compareTo("0")!=0)
            dHex="."+dHex;
        else
        {
            dHex="";
        }
        return minus?"-"+intHex+dHex:intHex+dHex;
    }