[gcc r11-7337] libstdc++: Fix endianness issue with IBM long double [PR98384]

[gcc r11-7337] libstdc++: Fix endianness issue with IBM long double [PR98384]

[Patrick Palka]

https://gcc.gnu.org/g:198c56052ea8cce4196e60c0dc3187bf3d67a786

commit r11-7337-g198c56052ea8cce4196e60c0dc3187bf3d67a786
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon Feb 22 21:49:25 2021 -0500

    libstdc++: Fix endianness issue with IBM long double [PR98384]
    
    The code in std::to_chars for extracting the high- and low-order parts
    of an IBM long double value does the right thing on powerpc64le, but not
    on powerpc64be.  This patch makes the extraction endian-agnostic, which
    fixes the execution FAIL of to_chars/long_double.cc on powerpc64be.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/98384
            * src/c++17/floating_to_chars.cc (get_ieee_repr): Extract
            the high- and low-order parts from an IBM long double value
            in an endian-agnostic way.

Diff:
---
 libstdc++-v3/src/c++17/floating_to_chars.cc | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/libstdc++-v3/src/c++17/floating_to_chars.cc b/libstdc++-v3/src/c++17/floating_to_chars.cc
index a50548acae7..4b2f85c1c1a 100644
--- a/libstdc++-v3/src/c++17/floating_to_chars.cc
+++ b/libstdc++-v3/src/c++17/floating_to_chars.cc
@@ -395,11 +395,11 @@ namespace
       // of the high part, and we merge the mantissa of the high part with the
       // mantissa (and the implicit leading bit) of the low part.
       using uint_t = unsigned __int128;
-      uint_t value_bits = 0;
-      memcpy(&value_bits, &value, sizeof(value_bits));
+      uint64_t value_bits[2] = {};
+      memcpy(value_bits, &value, sizeof(value_bits));
 
-      const uint64_t value_hi = value_bits;
-      const uint64_t value_lo = value_bits >> 64;
+      const uint64_t value_hi = value_bits[0];
+      const uint64_t value_lo = value_bits[1];
 
       uint64_t mantissa_hi = value_hi & ((1ull << 52) - 1);
       unsigned exponent_hi = (value_hi >> 52) & ((1ull << 11) - 1);