Arithmetic operation in Assembly

I am learning assembly language. I find that arithmetic in assembly can be either signed or unsigned. Rules are different for both type of arithmetic and I find it is programmer's headache to decide which ru开发者_运维问答les to apply. So a programmer should know beforehand if arithmetic involves the negative numbers or not. if yes, signed arithmetic rules should be used, else simpler and easier unsigned arithmetic will do. Main problem I find with unsigned arithmetic is ‘what if result is larger than its storage area?’. It can be easily solved by using a bigger-than-required storage area for the data. But that will consume extra bytes and size of data segment would increase. If size of the code is no issue, can't we use this technique freely?

If you are the programmer, you are in control of your data representation within the bounds of the requirements of your software's target domain. This means you need to know well before you actually start touching code what type of data you are going to be dealing with, how it is going to be arranged (in the case of complex data types) and how it is going to be encoded (floating-point/unsigned integer/signed integer, etc.). It is "safest" to use the operations that match the type of the data you're manipulating which, if you've done your design right, you should already know.

It's not that simple. Most arithmetic operations are sign agnostic: they are neither signed nor unsigned.

The interpretation of the result—which is determined by program specification—is what makes them signed or unsigned, not the operation itself. The proper flavor of compare instructions always have to be chosen carefully.

In some CPU architectures there are distinct signed and unsigned divide instructions, but that is about as far as it goes. Most CPUs have arithmetic shift right instruction flavors which either preserve the high bit or replace it with zero: that can be used as signed and unsigned handling, respectively.