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libstdc++: Fix endianness issue with IBM long double [PR98384]

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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.
This commit is contained in:
Patrick Palka 2021-02-22 21:49:25 -05:00
parent 635cf58ca3
commit 198c56052e
1 changed files with 4 additions and 4 deletions
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8
libstdc++-v3/src/c++17/floating_to_chars.cc
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@ -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);