Compiler/TM4C1290NCPDT: Access to Carry Bit

Michael Schuster said:

I'm adding to 32-Bit values (c-code) and want to evaluate the carry bit

Why? I'm trying to think of cases where it would be a) useful and b) well defined. I can't come up with any (especially b).

Robert

As so often noted - posters NEVER/EVER justify their (bit strange) requests...
As the initial answering post stated - poster (claimed) to be using "C" (negating such a need) - this (use of C) may prove NOT the (real) case!

Hi Robert,

did you see the link above (bisqwit.iki.fi/.../ and "Addition of larger integers than native register size").

I want to add large ints and thought it might be easier to get the carry directly than with a comparison as with the pseudo code :
uint_type a = original_1;
uint_type b = original_2;
uint_type result = a + b;
bool carry = result < a;

Michael Schuster said:

did you see the link above (bisqwit.iki.fi/.../ and "Addition of larger integers than native register size").

I don't follow links w/o at least some explanation of what hey are and I'm cautious even then.

Michael Schuster said:

I want to add large ints and thought it might be easier to get the carry directly than with a comparison as with the pseudo code :

You do realize that there is native support for this, far more efficient than anything you could write. At least up to 64bits. Beyond that there are available libraries.

Robert

Michael Schuster said:

I need 256 Bit. Well I can use the pseudo code, but I just was wondering howto have access to the carry bit.

There are readily available libraries that will do that for you .

I don't think there is, on any processor, a sure way of accessing the carry bit  after an addition. At the very least you'd need to play games with volatile. By the time you were done you'd likely be as far or further ahead to use assembly.

Robert