[gcc r15-3379] libsupc++: Fix handling of m68k extended real in <compare>

[Andreas Schwab]

https://gcc.gnu.org/g:4bf758b212170dba2b5a1881950e949ec4f8a58b

commit r15-3379-g4bf758b212170dba2b5a1881950e949ec4f8a58b
Author: Andreas Schwab <schwab@suse.de>
Date:   Mon Sep 2 10:43:20 2024 +0200

    libsupc++: Fix handling of m68k extended real in <compare>
    
            PR libstdc++/116513
            * libsupc++/compare (_S_fp_bits) [__fmt == _M68k_80bit]: Shift
            padding out of exponent word.

Diff:
---
 libstdc++-v3/libsupc++/compare | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/libsupc++/compare b/libstdc++-v3/libsupc++/compare
index 686aa6d218fe..63ad6b5c23e9 100644
--- a/libstdc++-v3/libsupc++/compare
+++ b/libstdc++-v3/libsupc++/compare
@@ -838,7 +838,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
 	      using enum _Fp_fmt;
 #endif
 	      constexpr auto __fmt = _S_fp_fmt<_Tp>();
-	      if constexpr (__fmt == _X86_80bit || __fmt == _M68k_80bit)
+	      if constexpr (__fmt == _X86_80bit)
 		{
 		  if constexpr (sizeof(_Tp) == 3 * sizeof(int32_t))
 		    {
@@ -851,6 +851,11 @@ namespace std _GLIBCXX_VISIBILITY(default)
 		      return _Int<int16_t>(__ival._M_hi, __ival._M_lo);
 		    }
 		}
+	      else if constexpr (__fmt == _M68k_80bit)
+		{
+		  auto __ival = __builtin_bit_cast(_Int<int32_t>, __val);
+		  return _Int<int16_t>(__ival._M_hi >> 16, __ival._M_lo);
+		}
 	      else if constexpr (sizeof(_Tp) == 2 * sizeof(int64_t))
 		{
 #if __SIZEOF_INT128__