How can I implement BCD in Fortran?

Question

Not sure if the title of my question makes sense, so bear with me. I'd like to find a system for representing single digit numbers with as few bits as possible. There is a method called "Densely packed decimal" (https://en.wikipedia.org/wiki/Densely_packed_decimal) which would be my ideal solution, but I wouldn't even know if that's possible or how I could implement it without further research or guidance from a guru.

The next best thing would be to be able to use a 4-bit addressing system to represent digits, but once again I'm not sure if that is even possible.

So! Barring implementations of the above methods/systems, I could settle for a 1-byte data type which I could use to represent pairs of two integers. Is there a 1-byte data-type in Fortran, or does it not allow for that level of control?

Answer 1

There is a 1 byte datatype in (almost) every programming language. It is the character. It is actually the definition of a byte, that it can hold a default character.

There is also a 1-byte (strictly speaking 1-octet) integer type in Fortran, accessible as integer(int8) where int8 is a constant from the iso_fortran_env module (Fortran 2008).

Both can be used to implement such things. Whether you will use division by other numbers, xoring, or Fortran bit manipulation intrinsic functions https://www.nsc.liu.se/~boein/f77to90/a5.html#section10 (probably the best option) is up to you.