[libc] [llvm] [libc] Move printf long double to simple calc (PR #75414)

[Guillaume Chatelet via llvm-commits]

https://github.com/gchatelet commented:

I find the code in `libc/src/__support/float_to_string.h` quite complicated. It's hard to grasp the overall algorithm, especially with the negative block indices. Is there a way to make it simpler? Maybe by introducing dedicated structures?

https://github.com/llvm/llvm-project/pull/75414