[PATCH][risc-v] libstdc++: Preserve signbit of nan when converting float to double [PR113578]

[Jonathan Wakely]

Do we want this change for RISC-V, to fix PR113578?

I haven't tested it on RISC-V, only on x86_64-linux (where it doesn't do
anything).

-- >8 --

libstdc++-v3/ChangeLog:

        PR libstdc++/113578
        * include/std/ostream (operator<<(basic_ostream&, float)):
        Restore signbit after converting to double.
---
 libstdc++-v3/include/std/ostream | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/libstdc++-v3/include/std/ostream b/libstdc++-v3/include/std/ostream
index 8a21758d0a3..d492168ca0e 100644
--- a/libstdc++-v3/include/std/ostream
+++ b/libstdc++-v3/include/std/ostream
@@ -233,7 +233,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       {
        // _GLIBCXX_RESOLVE_LIB_DEFECTS
        // 117. basic_ostream uses nonexistent num_put member functions.
+#ifdef __riscv
+       return _M_insert(__builtin_copysign((double)__f,
+                                           (double)-__builtin_signbit(__f));
+#else
        return _M_insert(static_cast<double>(__f));
+#endif
       }
 
       __ostream_type&
-- 
2.44.0