Hacker News Reader

Comment by samsquire | Hacker News Reader

Thanks for this.

There is a really good blog post to understand coroutines from an assembly perspective here: https://blog.dziban.net/coroutines/

I ported the intel assembly syntax in that blog post to at&t syntax and assembled it with GNU Assembler https://github.com/samsquire/assembly as coroutines.S

there is also protothreads and Tina http://dunkels.com/adam/pt/ https://github.com/slembcke/Tina

View on HN

No problem. If you have any questions feel free to ask.

My C is a bit rusty. What do (void*)0xcafe and (void*)0xbeef in the example mean?

The example just shows some of the functions for the library being used. Mainly the storing and returning of values. As for the numbers like "(void*)0xcafe" it's casting the number 0xcafe (in hex) to a void*. Why those constants they just easy to read in hex since they happen to spell a word. They could be anything, depending on your application like a pointer to data or some important constant ect...

Thanks, so void* is the any type in C. And the argument is not necessarily a pointer nor should it be dereferenced. I think I understand.

More particularly, I would describe it as a "pointer to anything". The size of the value will be exactly the size used for pointers in the given system (e.g. 8 bytes).

If you happen to know what a void* is pointing to, you can cast it to another type like "my_struct_t*" and deference the value. I would call it a work around for C lacking true polymorphism.

That is pretty much the opposite of what GP said: they're using void* to directly store an integer value rather than a pointer to anything (in that case).

Reply on news.ycombinator.com