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[libc][NFC] Zero out padding bits in the uint form of x86 FPBits<long double>.

This commit is contained in:
Siva Chandra Reddy 2020-07-28 11:43:04 -07:00
parent 6f00f3b56e
commit 9cc70e047c
1 changed files with 12 additions and 4 deletions
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16
libc/utils/FPUtil/LongDoubleBitsX86.h
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@ -23,10 +23,10 @@ template <> struct MantissaWidth<long double> {
template <unsigned Width> struct Padding;
// i386 padding.
template <> struct Padding<4> { static constexpr unsigned Value = 16; };
template <> struct Padding<4> { static constexpr unsigned value = 16; };
// x86_64 padding.
template <> struct Padding<8> { static constexpr unsigned Value = 48; };
template <> struct Padding<8> { static constexpr unsigned value = 48; };
template <> struct __attribute__((packed)) FPBits<long double> {
using UIntType = __uint128_t;
@ -38,7 +38,7 @@ template <> struct __attribute__((packed)) FPBits<long double> {
uint8_t implicitBit : 1;
uint16_t exponent : ExponentWidth<long double>::value;
uint8_t sign : 1;
uint64_t padding : Padding<sizeof(uintptr_t)>::Value;
uint64_t padding : Padding<sizeof(uintptr_t)>::value;
template <typename XType,
cpp::EnableIfType<cpp::IsSame<long double, XType>::Value, int> = 0>
@ -91,7 +91,15 @@ template <> struct __attribute__((packed)) FPBits<long double> {
// zero in case i386.
UIntType result = UIntType(0);
*reinterpret_cast<FPBits<long double> *>(&result) = *this;
return result;
// Even though we zero out |result| before copying the long double value,
// there can be garbage bits in the padding. So, we zero the padding bits
// in |result|.
static constexpr UIntType mask =
(UIntType(1) << (sizeof(long double) -
Padding<sizeof(uintptr_t)>::value / 8)) -
1;
return result & mask;
}
static FPBits<long double> zero() { return FPBits<long double>(0.0l); }