Converting to base60 from base10 value in Java

Question

http://convertxy.com/index.php/numberbases/

Here, we can see lots of base calculations.

https://stackoverflow.com/a/52474238/10309977

Here, they suggest only for base36. Upper case letters + numbers.

What i want is, to convert from long value (base 10 ) to upper + lower letters + numbers.

So, according to the first website, i can use such a method.

I want converting to base 10 from base 60 then incrementing.

How can i do this?

Because radix can be used for maximum base 36.

You will need to write some code. Btw, you can use a variety of bases eg 85 works pretty well as it packs 10 letters into a long. — Peter Lawrey, Nov 13 '18 at 09:26
@PeterLawrey i only need alphanumeric characters to increment. — vegan, Nov 13 '18 at 12:30

score 0 · Accepted Answer · edited Jun 20 '20 at 09:12

Here is the complete code, assuming A = 10 and a = 36 :

public static int base = 60;

public static void main(String[] args) {
    long test =0x7FFFFFFFFFFFFFFFL;
    System.out.println(test+ " -> "+convertBase10toCustomBase(test));

    String test2 = "FFDYWVtKFU7";
    System.out.println(test2+" -> "+convertCustomBasetoBase10(test2));

}
public static String convertBase10toCustomBase(long n){
    boolean negative = (n<0); // Remembers if n is negative.
    if (negative) n=-n; // Now works with a positive number
    String result= "";
    do {
        result= getBase((int)(n%base))+result;
        n/=base;
    }while(n>0);

    if(negative) result="-"+result;

    return result;
}
public static char getBase(int n){
    if(n<=9)
        return (char)(n+'0'); // Returns the char from numeric value
    if(n <35)
        return (char)('A'+ n -10); // Returns char in UpperCase if 9 < n < n+base 
    return (char)('a'+ n -36); // Returns in LowerCase otherwise
}

public static long convertCustomBasetoBase10(String s){

    boolean isNegative=false; // Remembers if the String starts with "-"
    if(s.charAt(0)=='-'){
        isNegative = true;
        s=s.substring(1); // Removes the "-" if negative
    }

    long result = 0;

    // Each char from right to left will be converted to a numeric value
    // Each numeric value must be multiplied by a certain power depending on its position, then added to previous ones.
    for (int i =0; i<s.length();i++)
        result += Math.pow(base,i)*getBase10(s.charAt(s.length()-i-1)); 

    if(isNegative) return -result;

    return result;

}
public static int getBase10(char c){
    // If the char represents a number, just return its value
    if (!Character.isLetter(c))
        return Character.getNumericValue(c);

    // If the char is UpperCase, we substract from it 
    // the value of 'A' and add 10 so that the first char A = 10
    if(Character.isUpperCase(c))
        return c -'A'+10;
    // If LowerCase, we substract  the value of 'a' and add 10+26
    return c-'a'+36;
}

Displays :

9223372036854775807 -> FFDYWVtKFU7

FFDYWVtKFU7 -> 9223372036854775807

EDIT : Thanks to Peter Lawrey for suggesting to calculate directly with char values instead of using an array of char.

`Math.pow(base,i)` is only accurate to 53-bits. It won't work for 63-bit values. — Peter Lawrey, Nov 13 '18 at 17:02
You can calcuate `'A' + n - 10` and `'a' + n - 10 - 26` so you don't need an array. Instead of searching through an array you can calculate `c - 'A' + 10` — Peter Lawrey, Nov 13 '18 at 17:04
Thanks for the great tip. As for pow, it seems to work with a 63 bits long value. A java update maybe ? I can't find documentation on this matter. — Whole Brain, Nov 14 '18 at 13:08

Converting to base60 from base10 value in Java

1 Answers1