Question

I’m attempting to implement a random number generator system; essentially I’m reading in an SHA1 hash, which then gets converted into a BigInteger value:

String start = "abc";
String hash = utils.SHA1(start); //Generates an SHA1 hash of the string
byte[] bytes = hash.getBytes();
BigInteger big = new BigInteger(bytes);

This code generates a BigInteger with a value of:

811203900027758629330492243480887228261034167773619203962320290854945165232584286910163772258660

What I need to somehow do (and this is where I get confused), is reduce that number into a much shorter number with a fixed number of decimal places.

Using a combination of modular arithmetic and Java Math API functions, is there a sensible way of reducing this number down into a 3 digit number. Or any other length of number I choose.

At the moment I’m just simply converting that huge number into a String, and then taking a substring of the length of number I want. However I’m not entirely happy with this as the numbers I get aren’t that random, as the range is somewhat limited with 3 digits.

The whole purpose of this is for the newly generated random x digit number to be then converted into a string using a radix of 36, to also include ASCII alphabet characters.

Any information or advice would be greatly appreciated.

Thanks!!

Answer 1

Yes you can use modulus like .mod(1000) or for base 36 .mod(36*36*36) or even plain .longValue() % 1000 or .longValue() % (36*36*36)

You can use Long.toString(x, 10) or Long.toString(x, 36)

Not sure I can tell much more without giving you the answer.