Question

As we all know a byte range is 0 to 255
i have two byte, I want to create another number that is reversible but with minimum length that combine these two number and create a new one, the simplest solution is

a = b1 * 1000 + b2

reverse would be

b1 = a / 1000
b2 = a % 1000

the length of above solution varying 0 to 6 length, i want a formula with FIXED and minimum length

Answer 1

Encode:

x = b1 * 256 + b2;
x = x + 10000;

Decode:

x = x - 10000;
b1 = x >> 8;
b2 = x & 255;

Encoded result always has length 5 (10000 through 75535 inclusive). And since there are 65536 different pairs (b1, b2) you can’t encode them into numbers of length < 5 (because there are at most 10000 such numbers).