long double becomes u128

Input C/C++ Header

typedef long double foo

Bindgen Invocation

$ bindgen input.h 

Actual Results

/* automatically generated by rust-bindgen */

pub type a = u128;

Expected Results

I'm not entirely sure. Here are the idea's I can think of

• use f64, but that leeds to it's own set of issues (#1529).
• use the f128 crate but the layout of the f128 is different to the layout of a c long double
• add a c_longdouble type to std::os::raw. The problem is that on many machines (including mine) long double is a 16 byte float, which rust doesn't suport
• Through an error. This will avoid confusion, but also make also will mean losing suport for many .h files
• use u128. The problem here is were treating a float as an int, and that will mean all sorts of problems

Start by reproducing the issue with the shown input.h and bindgen invocation, then read the discussion around the listed expected-result options and issue #1529. Done means the project has an agreed, tested handling for C/C++ long double that avoids silently representing it as u128.