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libstdc++: Avoid implicit narrowing from uint128_t [PR104859]

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We need to be explicit about narrowing conversions from uint128_t since,
on targets that lack __int128, this type is defined as an integer-class
type that is only _explicitly_ convertible to the builtin integer types.
This issue was latent until r12-7563-ge32869a17b788b made the frontend
correctly reject explicit conversion functions during (dependent)
copy-initialization.

	PR libstdc++/104859

libstdc++-v3/ChangeLog:

	* src/c++17/floating_to_chars.cc (__floating_to_chars_hex):
	Be explicit when narrowing the shifted effective_mantissa,
	since it may have an integer-class type.
This commit is contained in:
Patrick Palka 2022-03-09 18:48:52 -05:00
parent 4ea128d5c7
commit 65857caee8
1 changed files with 3 additions and 3 deletions
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6
libstdc++-v3/src/c++17/floating_to_chars.cc
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@ -801,14 +801,14 @@ template<typename T>
char leading_hexit;
if constexpr (has_implicit_leading_bit)
{
const unsigned nibble = effective_mantissa >> rounded_mantissa_bits;
const auto nibble = unsigned(effective_mantissa >> rounded_mantissa_bits);
__glibcxx_assert(nibble <= 2);
leading_hexit = '0' + nibble;
effective_mantissa &= ~(mantissa_t{0b11} << rounded_mantissa_bits);
}
else
{
const unsigned nibble = effective_mantissa >> (rounded_mantissa_bits-4);
const auto nibble = unsigned(effective_mantissa >> (rounded_mantissa_bits-4));
__glibcxx_assert(nibble < 16);
leading_hexit = "0123456789abcdef"[nibble];
effective_mantissa &= ~(mantissa_t{0b1111} << (rounded_mantissa_bits-4));
@ -853,7 +853,7 @@ template<typename T>
while (effective_mantissa != 0)
{
nibble_offset -= 4;
const unsigned nibble = effective_mantissa >> nibble_offset;
const auto nibble = unsigned(effective_mantissa >> nibble_offset);
__glibcxx_assert(nibble < 16);
*first++ = "0123456789abcdef"[nibble];
++written_hexits;