Question

In my app I need to run a 5 digits number through an algorithm and return a number between the given interval, ie:

The function encode, gets 3 parameters, 5 digits initial number, interval lower limit and interval superior limit, for example:
int res=encode(12879,10,100) returns 83.

The function starts from 12879 and does something with the numbers and returns a number between 10 and 100. This mustn’t be random, every time I pass the number 12879 to the encode function must always return the same number.

Any ideas?

Thanks,
Direz

Answer 1

One possible approach:

1. compute the range of your interval R = (100 – 10) + 1
2. compute a hash modulo R of the input H = hash(12879) % R
3. add the lower bound to the modular hash V = 10 + H

Here the thing though – you haven’t defined any constraints or requirements on the “algorithm” that produces the result. If all you want is to map a value into a given range (without any knowledge of the distribution of the input, or how input values may cluster, etc), you could just as easily just take the range modulo of the input without hashing (as Foo Bah demonstrates).

If there are certain constraints, requirements, or distributions of the input or output of your encode method, then the approach may need to be quite different. However, you are the only one who knows what additional requirements you have.