Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 235 insertions, 0 deletions

diff --git a/mozglue/baseprofiler/public/ProportionValue.h b/mozglue/baseprofiler/public/ProportionValue.h
new file mode 100644
index 0000000000..61eb2766ec
--- /dev/null
+++ b/mozglue/baseprofiler/public/ProportionValue.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef ProportionValue_h
+#define ProportionValue_h
+
+#include "mozilla/Attributes.h"
+
+#include <algorithm>
+#include <limits>
+
+namespace mozilla {
+
+// Class storing a proportion value between 0 and 1, effectively 0% to 100%.
+// The public interface deals with doubles, but internally the value is encoded
+// in an integral type, so arithmetic operations are fast.
+// It also supports an invalid value: Use MakeInvalid() to construct, it infects
+// any operation, and gets converted to a signaling NaN.
+class ProportionValue {
+ public:
+  using UnderlyingType = uint32_t;
+
+  // Default-construct at 0%.
+  constexpr ProportionValue()
+      // This `noexcept` is necessary to avoid a build error when encapsulating
+      // `ProportionValue` in `std::Atomic`:
+      // "use of deleted function
+      // 'constexpr std::atomic<mozilla::ProportionValue>::atomic()"
+      // because the default `std::atomic<T>::atomic()` constructor is marked:
+      // `noexcept(std::is_nothrow_default_constructible_v<T>)`
+      // and therefore this default constructor here must be explicitly marked
+      // `noexcept` as well.
+      noexcept
+      : mIntegralValue(0u) {}
+
+  // Construct a ProportionValue with the given value, clamped to 0..1.
+  // Note that it's constexpr, so construction from literal numbers should incur
+  // no runtime costs.
+  // If `aValue` is NaN, behavior is undefined! Use `MakeInvalid()` instead.
+  constexpr explicit ProportionValue(double aValue)
+      : mIntegralValue(UnderlyingType(std::clamp(aValue, 0.0, 1.0) * scMaxD)) {}
+
+  [[nodiscard]] static constexpr ProportionValue MakeInvalid() {
+    return ProportionValue(scInvalidU, Internal{});
+  }
+
+  [[nodiscard]] constexpr double ToDouble() const {
+    return IsInvalid() ? std::numeric_limits<double>::signaling_NaN()
+                       : (double(mIntegralValue) * scInvMaxD);
+  }
+
+  // Retrieve the underlying integral value, for storage or testing purposes.
+  [[nodiscard]] constexpr UnderlyingType ToUnderlyingType() const {
+    return mIntegralValue;
+  };
+
+  // Re-construct a ProportionValue from an underlying integral value.
+  [[nodiscard]] static constexpr ProportionValue FromUnderlyingType(
+      UnderlyingType aUnderlyingType) {
+    return ProportionValue(
+        (aUnderlyingType <= scMaxU) ? aUnderlyingType : scInvalidU, Internal{});
+  }
+
+  [[nodiscard]] constexpr bool IsExactlyZero() const {
+    return mIntegralValue == 0u;
+  }
+
+  [[nodiscard]] constexpr bool IsExactlyOne() const {
+    return mIntegralValue == scMaxU;
+  }
+
+  [[nodiscard]] constexpr bool IsValid() const {
+    // Compare to the maximum value, not just exactly scInvalidU, to catch any
+    // kind of invalid state.
+    return mIntegralValue <= scMaxU;
+  }
+  [[nodiscard]] constexpr bool IsInvalid() const {
+    // Compare to the maximum value, not just exactly scInvalidU, to catch any
+    // kind of invalid state.
+    return mIntegralValue > scMaxU;
+  }
+
+  // Strict comparisons based on the underlying integral value. Use
+  // `CompareWithin` instead to make fuzzy comparisons.
+  // `ProportionValue::MakeInvalid()`s are equal, and greater than anything
+  // else; Best to avoid comparisons, and first use IsInvalid() instead.
+#define OPERATOR_COMPARISON(CMP)                                  \
+  [[nodiscard]] constexpr friend bool operator CMP(               \
+      const ProportionValue& aLHS, const ProportionValue& aRHS) { \
+    return aLHS.mIntegralValue CMP aRHS.mIntegralValue;           \
+  }
+  OPERATOR_COMPARISON(==)
+  OPERATOR_COMPARISON(!=)
+  OPERATOR_COMPARISON(<)
+  OPERATOR_COMPARISON(<=)
+  OPERATOR_COMPARISON(>)
+  OPERATOR_COMPARISON(>=)
+#undef OPERATOR_COMPARISON
+
+  // Arithmetic operations + - *, all working on the underlying integral values
+  // (i.e, no expensive floating-point operations are used), and always clamping
+  // to 0..1 range. Invalid values are poisonous.
+
+  [[nodiscard]] constexpr ProportionValue operator+(
+      ProportionValue aRHS) const {
+    return ProportionValue(
+        (IsInvalid() || aRHS.IsInvalid())
+            ? scInvalidU
+            // Adding fixed-point values keep the same scale, so there is no
+            // adjustment needed for that. [0,1]+[0,1]=[0,2], so we only need to
+            // ensure that the result is capped at max 1, aka scMaxU:
+            // a+b<=max <=> b<=max-a, so b is at maximum max-a.
+            : (mIntegralValue +
+               std::min(aRHS.mIntegralValue, scMaxU - mIntegralValue)),
+        Internal{});
+  }
+
+  [[nodiscard]] constexpr ProportionValue operator-(
+      ProportionValue aRHS) const {
+    return ProportionValue(
+        (IsInvalid() || aRHS.IsInvalid())
+            ? scInvalidU
+            // Subtracting fixed-point values keep the same scale, so there is
+            // no adjustment needed for that. [0,1]-[0,1]=[-1,1], so we only
+            // need to ensure that the value is positive:
+            // a-b>=0 <=> b<=a, so b is at maximum a.
+            : (mIntegralValue - std::min(aRHS.mIntegralValue, mIntegralValue)),
+        Internal{});
+  }
+
+  [[nodiscard]] constexpr ProportionValue operator*(
+      ProportionValue aRHS) const {
+    // Type to hold the full result of multiplying two maximum numbers.
+    using DoublePrecisionType = uint64_t;
+    static_assert(sizeof(DoublePrecisionType) >= 2 * sizeof(UnderlyingType));
+    return ProportionValue(
+        (IsInvalid() || aRHS.IsInvalid())
+            ? scInvalidU
+            // Multiplying fixed-point values doubles the scale (2^31 -> 2^62),
+            // so we need to adjust the result by dividing it by one scale
+            // (which is optimized into a binary right-shift).
+            : (UnderlyingType((DoublePrecisionType(mIntegralValue) *
+                               DoublePrecisionType(aRHS.mIntegralValue)) /
+                              DoublePrecisionType(scMaxU))),
+        Internal{});
+  }
+
+  // Explicitly forbid divisions, they make little sense, and would almost
+  // always return a clamped 100% (E.g.: 50% / 10% = 0.5 / 0.1 = 5 = 500%).
+  [[nodiscard]] constexpr ProportionValue operator/(
+      ProportionValue aRHS) const = delete;
+
+  // Division by a positive integer value, useful to split an interval in equal
+  // parts (with maybe some spare space at the end, because it is rounded down).
+  // Division by 0 produces an invalid value.
+  [[nodiscard]] constexpr ProportionValue operator/(uint32_t aDivisor) const {
+    return ProportionValue((IsInvalid() || aDivisor == 0u)
+                               ? scInvalidU
+                               : (mIntegralValue / aDivisor),
+                           Internal{});
+  }
+
+  // Multiplication by a positive integer value, useful as inverse of the
+  // integer division above. But it may be lossy because the division is rounded
+  // down, therefore: PV - u < (PV / u) * u <= PV.
+  // Clamped to 100% max.
+  [[nodiscard]] constexpr ProportionValue operator*(
+      uint32_t aMultiplier) const {
+    return ProportionValue(IsInvalid()
+                               ? scInvalidU
+                               : ((aMultiplier > scMaxU / mIntegralValue)
+                                      ? scMaxU
+                                      : (mIntegralValue * aMultiplier)),
+                           Internal{});
+  }
+
+ private:
+  // Tagged constructor for internal construction from the UnderlyingType, so
+  // that it is never ambiguously considered in constructions from one number.
+  struct Internal {};
+  constexpr ProportionValue(UnderlyingType aIntegralValue, Internal)
+      : mIntegralValue(aIntegralValue) {}
+
+  // Use all but 1 bit for the fractional part.
+  // Valid values can go from 0b0 (0%) up to 0b1000...00 (scMaxU aka 100%).
+  static constexpr unsigned scFractionalBits = sizeof(UnderlyingType) * 8 - 1;
+  // Maximum value corresponding to 1.0 or 100%.
+  static constexpr UnderlyingType scMaxU = UnderlyingType(1u)
+                                           << scFractionalBits;
+  // This maximum value corresponding to 1.0 can also be seen as the scaling
+  // factor from any [0,1] `double` value to the internal integral value.
+  static constexpr double scMaxD = double(scMaxU);
+  // The inverse can be used to convert the internal value back to [0,1].
+  static constexpr double scInvMaxD = 1.0 / scMaxD;
+
+  // Special value outside [0,max], used to construct invalid values.
+  static constexpr UnderlyingType scInvalidU = ~UnderlyingType(0u);
+
+  // Internal integral value, guaranteed to always be <= scMaxU, or scInvalidU.
+  // This is effectively a fixed-point value using 1 bit for the integer part
+  // and 31 bits for the fractional part.
+  // It is roughly equal to the `double` value [0,1] multiplied by scMaxD.
+  UnderlyingType mIntegralValue;
+};
+
+namespace literals {
+inline namespace ProportionValue_literals {
+
+// User-defined literal for integer percentages, e.g.: `10_pc`, `100_pc`
+// (equivalent to `ProportionValue{0.1}` and `ProportionValue{1.0}`).
+// Clamped to [0, 100]_pc.
+[[nodiscard]] constexpr ProportionValue operator""_pc(
+    unsigned long long int aPercentage) {
+  return ProportionValue{
+      double(std::clamp<unsigned long long int>(aPercentage, 0u, 100u)) /
+      100.0};
+}
+
+// User-defined literal for non-integer percentages, e.g.: `12.3_pc`, `100.0_pc`
+// (equivalent to `ProportionValue{0.123}` and `ProportionValue{1.0}`).
+// Clamped to [0.0, 100.0]_pc.
+[[nodiscard]] constexpr ProportionValue operator""_pc(long double aPercentage) {
+  return ProportionValue{
+      double(std::clamp<long double>(aPercentage, 0.0, 100.0)) / 100.0};
+}
+
+}  // namespace ProportionValue_literals
+}  // namespace literals
+
+}  // namespace mozilla
+
+#endif  // ProportionValue_h