CODEWITHSUNDEEP
javaalgorithmhexdecimal
isxaker
isxaker

Reputation: 9456

Need some explanation about how the hex to decimal algorithm works

The algorithm below converts hex to decimal, but I've confused, how this solution works?

public static int hex2decimal(String s) {
    String digits = "0123456789ABCDEF";
    s = s.toUpperCase();
    int val = 0;
    for (int i = 0; i < s.length(); i++) {
        char c = s.charAt(i);
        int d = digits.indexOf(c);
        val = 16*val + d;
    }
    return val;
}

source

I had known only one approach to do that before I found out this one. I mean, everyone knows: X*16^Y where X is the number you want to convert and Y is the position for the number (begging from the end to the start).

So, if you want to convert DA145 to decimal would be...

*(5 * 16^0) + (4 * 16^1) + (1 * 16^2) + (10 * 16^3) + (13 * 16^4)*

Upvotes: 0

Views: 96

Answers (2)

skyking
skyking

Reputation: 14360

This algorithm uses the fact that we can calculate 16^Y by repeatedly multiply together 16's and also that we can factor out common multiplications by 16. From your example you would instead end at:

13*16 + 10)*16 + 1)*16 + 4)*16 + 5

I've omitted the leading parentheses, as you see it happens to be that 13 is in effect multiplied with 16 four times.

Upvotes: 5

ctst
ctst

Reputation: 1680

The algorithm does pretty much the same as you would do it. It takes a String and compares every single char with the given value. This value is evaluated by digits, at which position it stands (e.g. A is in the 10th position, since we start counting with 0). This allows to easily change it e.g. to a 17 digit system instead of hexadezimal.

Edit: About the powers of 16, look at @skykings answer.

Upvotes: 1

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