This patch adds the r, R, k, and K conversion specifiers to printf, with
accompanying tests. They are guarded behind the
LIBC_COPT_PRINTF_DISABLE_FIXED_POINT flag as well as automatic fixed
point support detection.
The Ryu algorithm is very fast with its table, but that table grows too
large for long doubles. This patch adds a method of calculating the
digits of long doubles using just wide integers and fast modulo
operations. This results in significant performance improvements vs the
previous int calc mode, while taking up a similar amound of peak memory.
It will be slow in some %e/%g cases, but reasonable fast for %f with no
loss of accuracy.
In a previous patch, the printf writer was rewritten to use a single
writer class with a buffer and a callback hook. This patch refactors
scanf's reader to match conceptually.
In the document on undefined behavior, I noted that writing down your
decisions is very important. This document contains all the information
for compile flags and undefined behavior for our printf.
Reviewed By: sivachandra
Differential Revision: https://reviews.llvm.org/D158311
