long double miscompiles

[VorpalBlade]

Given:

#define _GNU_SOURCE
#include <stdio.h>
#include <math.h>

#define _PI_180 (M_PIl / 180.0)
#define _180_PI (180.0 / M_PIl)

int main(void) {
    printf("%LF\n", _PI_180);
    printf("%LF\n", _180_PI);
    return 0;
}

$ ./c-test
0.017453
57.295780

But the converted rust version:

$ target/debug/test 
-NAN
-NAN

The generated code is:

#![allow(dead_code, mutable_transmutes, non_camel_case_types, non_snake_case, non_upper_case_globals, unused_assignments, unused_mut)]
use ::c2rust_out::*;
extern "C" {
    fn printf(_: *const libc::c_char, _: ...) -> libc::c_int;
}
unsafe fn main_0() -> libc::c_int {
    printf(
        b"%LF\n\0" as *const u8 as *const libc::c_char,
        f128::f128::new(3.141592653589793238462643383279502884)
            / f128::f128::new(180.0f64),
    );
    printf(
        b"%LF\n\0" as *const u8 as *const libc::c_char,
        f128::f128::new(180.0f64)
            / f128::f128::new(3.141592653589793238462643383279502884),
    );
    return 0 as libc::c_int;
}
pub fn main() {
    unsafe { ::std::process::exit(main_0() as i32) }
}

I suspect (but have not checked that) f128 is not compatible with x87 80-bit long double and this conversion is just incorrect!

Software versions:

• Arch Linux (rolling release distro).
• glibc 2.37-2
• clang 15.0.7-1
• rustc 1.67.1 (from rustup)
• c2rust 0.17.0 (from cargo install)