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[libc][NFC] fix uint128 init in float properties #75084

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merged 1 commit into from
Dec 11, 2023
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[libc][NFC] fix uint128 init in float properties #75084

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6 changes: 4 additions & 2 deletions libc/src/__support/FPUtil/FloatProperties.h
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Original file line number Diff line number Diff line change
Expand Up @@ -85,7 +85,9 @@ template <typename T, size_t count> static constexpr T mask_trailing_ones() {
static_assert(cpp::is_unsigned_v<T>);
constexpr unsigned t_bits = CHAR_BIT * sizeof(T);
static_assert(count <= t_bits && "Invalid bit index");
return count == 0 ? 0 : (T(-1) >> (t_bits - count));
// It's important not to initialize T with -1, since T may be BigInt which
// will take -1 as a uint64_t and only initialize the low 64 bits.
return count == 0 ? 0 : ((~T(0)) >> (t_bits - count));
}

// Derives more properties from 'FPBaseProperties' above.
Expand Down Expand Up @@ -131,7 +133,7 @@ struct FPCommonProperties : private FPBaseProperties<fp_type> {
LIBC_INLINE_VAR static constexpr UIntType FP_MASK =
mask_trailing_ones<UIntType, TOTAL_BITS>();
static_assert((SIG_MASK & EXP_MASK & SIGN_MASK_) == 0, "masks disjoint");
static_assert((SIG_MASK | EXP_MASK | SIGN_MASK_) == FP_MASK, "masks covers");
static_assert((SIG_MASK | EXP_MASK | SIGN_MASK_) == FP_MASK, "masks cover");

LIBC_INLINE static constexpr UIntType bit_at(int position) {
return UIntType(1) << position;
Expand Down