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Unified Diff: base/numerics/safe_conversions.h

Issue 2589973003: Revert of Improve saturated_cast performance (Closed)
Patch Set: Created 4 years ago
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Index: base/numerics/safe_conversions.h
diff --git a/base/numerics/safe_conversions.h b/base/numerics/safe_conversions.h
index 99cbef4ca814c669514c0a206e6162458ed8c8e5..66b278ff3d3e41b3ce33f1d56bea183f12dc7b61 100644
--- a/base/numerics/safe_conversions.h
+++ b/base/numerics/safe_conversions.h
@@ -110,35 +110,35 @@
// that the specified numeric conversion will saturate by default rather than
// overflow or underflow, and NaN assignment to an integral will return 0.
// All boundary condition behaviors can be overriden with a custom handler.
-template <template <typename>
- class SaturationHandler = SaturatedCastDefaultHandler,
- typename Dst,
- typename Src>
-constexpr Dst saturated_cast_impl(const Src value,
- const RangeConstraint constraint) {
- return constraint.IsValid()
- ? static_cast<Dst>(value)
- : (constraint.IsOverflow()
- ? SaturationHandler<Dst>::HandleOverflow()
- // Skip this check for integral Src, which cannot be NaN.
- : (std::is_integral<Src>::value || constraint.IsUnderflow()
- ? SaturationHandler<Dst>::HandleUnderflow()
- : SaturationHandler<Dst>::HandleNaN()));
-}
-
-// saturated_cast<> is analogous to static_cast<> for numeric types, except
-// that the specified numeric conversion will saturate by default rather than
-// overflow or underflow, and NaN assignment to an integral will return 0.
-// All boundary condition behaviors can be overriden with a custom handler.
template <typename Dst,
template <typename>
class SaturationHandler = SaturatedCastDefaultHandler,
typename Src>
constexpr Dst saturated_cast(Src value) {
+ static_assert(
+ SaturationHandler<Dst>::lowest() < SaturationHandler<Dst>::max(), "");
+ // While this looks like a lot of code, it's all constexpr and all but
+ // one variable are compile-time constants (enforced by a static_assert).
+ // So, it should evaluate to the minimum number of comparisons required
+ // for the range check, which is 0-3, depending on the exact source and
+ // destination types, and whatever custom range is specified.
using SrcType = typename UnderlyingType<Src>::type;
- return saturated_cast_impl<SaturationHandler, Dst>(
- static_cast<SrcType>(value),
- DstRangeRelationToSrcRange<Dst, SaturationHandler, SrcType>(value));
+ return IsGreaterOrEqual<SrcType, Dst>::Test(
+ value, NarrowingRange<Dst, SrcType, SaturationHandler>::lowest())
+ ? (IsLessOrEqual<SrcType, Dst>::Test(
+ value,
+ NarrowingRange<Dst, SrcType, SaturationHandler>::max())
+ ? static_cast<Dst>(value)
+ : SaturationHandler<Dst>::HandleOverflow())
+ // This last branch is a little confusing. It's specifically to
+ // catch NaN when converting from float to integral.
+ : (std::is_integral<SrcType>::value ||
+ std::is_floating_point<Dst>::value ||
+ IsLessOrEqual<SrcType, Dst>::Test(
+ value, NarrowingRange<Dst, SrcType,
+ SaturationHandler>::max())
+ ? SaturationHandler<Dst>::HandleUnderflow()
+ : SaturationHandler<Dst>::HandleNaN());
}
// strict_cast<> is analogous to static_cast<> for numeric types, except that
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