Building an OS - 5 - How to implement printf

How to implement printf without any standard libraries, from parsing the format string, passing variadic arguments to formatting numbers and implementing x86 division.

Links:

Tools:

Documentation:
- OpenWatcom manuals (in installation directory)

Chapters:
0:00 Introduction
0:38 The plan
1:44 Passing varargs
7:07 Parsing the format string
12:35 Implementation
20:36 Division issues
23:41 Long division
25:25 Implementation of long division
28:55 Conclusion

[raxneff]

such high quality content (including the filming aspects) for such a small channel!

[ewhitest]

Thank you for these videos, definitely the best resource I've found on these fun topics. Also, I am grateful for you describing the problems you run into and how you work around them!

[Maid-Shaymim]

For a bit there, i was a little confused, wasn't getting the proper output and I assumed for a while that it was from my C code, but after some trial and error I found that it was in the assembly! yippee for problem solving :)

[perhaps]

holy shit i just discovered the holy grail of creating an os,
dude thank you so much for making such high quality videos, words can't express my appreciation you are awesome!!

[DevonBagley]

Programmers opposition to goto isn't primarily a safety concern. It's a readability, and maintainability concern.

It can become hard to reason about the flow of the program when goto is breaking normal flow control. This isn't really a concern for anyone intimately familiar with the code. Only for later maintainers.

As you are nesting switches and implementing the entire state machine within a single function it's pretty obvious that having maintainers other than yourself is not a concern of yours either. 😅

[somethingwithtech]

Part 2 of documenting my errors: I was missing a break; instruction in the PRINTF_STATE_NORMAL case, completly jumbling my output

[WareXProvider]

You use `bits 16` while using 32-bit eax and ecx registers! Why the heck it works?!

[Ahuenen-tz]

Когда я вставляю реализацию printf в файл stdio.с и он становится больше, то при запуске кода в qemu я получаю сообщение "Read from disk failed" из загрузчика, в чем может быть проблема? Причем если я оставляю только puts, putc и удаляю реализацию printf, то все работает нормально

[arielfuxman]

Why did you choose argp to be a pointer to an int?