Seems unlikely. My spot check of the the two vfprintf implementations shows no flow from one to the other, and shows that part of the Cosmopolitan code has an older lineage than nolibc.
The nolibc source has many reference to copyright held by "Willy Tarreau", under LGPL-2.1 OR MIT license, with a copyright date starting in 2017.
The string "Tarreau" does not exist in the Cosmopolitan library, so that's a strong negative there. Let's look closer.
The file organization is quite different. And so is the implementation. So that's another negative.
Right away we can see nolibc places many functions in the same file while Cosmopolitan uses a one-function-per-filename organization.
Cosmopolitan's fvprintf locks the file (which nolibc doesn't need to do) then calls vfprintf_unlocked which calls __fmt at https://github.com/jart/cosmopolitan/blob/master/libc/fmt/fm... , which is the actual implementation. It look very different from NOLIBC's.
Okay, so perhaps that's they way now but not at the beginning?
I can confirm that the code looks totally different. Anyway there's no reason someone writing a libc would waste their time with pieces of code from other provenance. It takes less time to write a minimalist printf than trying to adapt an existing one to your exact needs, types, validity domains etc, and it'll be easier to extend yours that someone else's. You can write it however you want, it will always end up with a loop around a switch/case :-)
