diff options
| author | Thiago Macieira <thiago.macieira@intel.com> | 2021-11-27 20:02:57 -0800 |
|---|---|---|
| committer | Thiago Macieira <thiago.macieira@intel.com> | 2022-01-14 09:57:40 -0800 |
| commit | 0ca6ad8cfc0827775e5bf001cd8d17f247a1400f (patch) | |
| tree | 841b51b08d392d6388782b529b729c23bd5ab514 /src/corelib/global | |
| parent | dd3c4cb9bfc965ae40e914216862fbb350c55992 (diff) | |
convertDoubleTo: move the precision upgrade test up
Hopefully, the compiler will realize that the suprema calculated below
are actually bigger than these limits and make the appropriate dead code
eliminations.
Change-Id: I89446ea06b5742efb194fffd16bb99f78b26eb0e
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
Diffstat (limited to 'src/corelib/global')
| -rw-r--r-- | src/corelib/global/qnumeric_p.h | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/src/corelib/global/qnumeric_p.h b/src/corelib/global/qnumeric_p.h index 823a1812de..bb3f1a976b 100644 --- a/src/corelib/global/qnumeric_p.h +++ b/src/corelib/global/qnumeric_p.h @@ -189,6 +189,19 @@ template<typename T> static inline bool convertDoubleTo(double v, T *value, bool allow_precision_upgrade = true) { static_assert(std::numeric_limits<T>::is_integer); + static_assert(std::is_integral_v<T>); + constexpr bool TypeIsLarger = std::numeric_limits<T>::digits > std::numeric_limits<double>::digits; + + if constexpr (TypeIsLarger) { + using S = std::make_signed_t<T>; + constexpr S max_mantissa = S(1) << std::numeric_limits<double>::digits; + // T has more bits than double's mantissa, so don't allow "upgrading" + // to T (makes it look like the number had more precision than really + // was transmitted) + if (!allow_precision_upgrade && (v > double(max_mantissa) || v < double(-max_mantissa - 1))) + return false; + } + // The [conv.fpint] (7.10 Floating-integral conversions) section of the C++ // standard says only exact conversions are guaranteed. Converting @@ -211,10 +224,6 @@ static inline bool convertDoubleTo(double v, T *value, bool allow_precision_upgr supremum = -2.0 * std::numeric_limits<ST>::min(); // -2 * (-2^63) = 2^64, exact (for T = quint64) v = fabs(v); } - if (std::is_integral<T>::value && sizeof(T) > 4 && !allow_precision_upgrade) { - if (v > double(Q_INT64_C(1)<<53) || v < double(-((Q_INT64_C(1)<<53) + 1))) - return false; - } *value = std::numeric_limits<T>::max(); if (v >= supremum) |