[libc-commits] [libc] [libc][docs] Update website to reflect new strategy (PR #168637)

[Nikolas Klauser via libc-commits]

================
@@ -0,0 +1,41 @@
+.. _hand_in_hand:
+
+============
+Hand-in-Hand
+============
+
+Hand-in-Hand is the name of the mechanism that allows other LLVM projects to use
+LLVM-libc's internal C++ APIs instead of calling the public libc interface.
+This is useful for cases where the C interface doesn't match the desired
+interface.
+
+The original use case for the Hand-in-Hand interface was to let libc++ use
+LLVM-libc's string to float conversion internals. The libc interface (strtof)
+takes a null terminated string with no maximum length while the libc++ interface
+(from_chars<float>) takes a string with a start and an end. If libc++ had used
+the public interface it would have had to allocate a new null terminated string
+before calling strtof, but with Hand-in-Hand libc++ handles its own parsing
+and then passes the parsed information to LLVM-libc's conversion code. This is
+better for performance and cuts down on code duplication in the LLVM repository.
+
+Hand-in-Hand works by LLVM-libc exposing a set of headers in the /libc/shared/
+directory. These headers make the interface more explicit and easier to
+maintain. The client library includes the shared headers by depending on the
+llvm-libc-common-utilities target which sets up the necessary includes and
+defines. The client library then includes "shared/<header>" to get the necessary
+components. All of the functions shared via Hand-in-Hand are header only.
+
+The Hand-in-Hand interface is intended to be an internal implementation detail,
+and is has no guarantees of stability. When the internal LLVM-libc interface is
----------------
philnik777 wrote:

```suggestion
and it has no guarantees of stability. When the internal LLVM-libc interface is
```

https://github.com/llvm/llvm-project/pull/168637