summaryrefslogtreecommitdiffstats
path: root/mfbt/Saturate.h
diff options
context:
space:
mode:
Diffstat (limited to '')
-rw-r--r--mfbt/Saturate.h248
1 files changed, 248 insertions, 0 deletions
diff --git a/mfbt/Saturate.h b/mfbt/Saturate.h
new file mode 100644
index 0000000000..777e326934
--- /dev/null
+++ b/mfbt/Saturate.h
@@ -0,0 +1,248 @@
+/* -*- 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/. */
+
+/* Provides saturation arithmetics for scalar types. */
+
+#ifndef mozilla_Saturate_h
+#define mozilla_Saturate_h
+
+#include <limits>
+#include <stdint.h>
+#include <type_traits>
+#include <utility>
+
+#include "mozilla/Attributes.h"
+
+namespace mozilla {
+namespace detail {
+
+/**
+ * |SaturateOp<T>| wraps scalar values for saturation arithmetics. Usage:
+ *
+ * uint32_t value = 1;
+ *
+ * ++SaturateOp<uint32_t>(value); // value is 2
+ * --SaturateOp<uint32_t>(value); // value is 1
+ * --SaturateOp<uint32_t>(value); // value is 0
+ * --SaturateOp<uint32_t>(value); // value is still 0
+ *
+ * Please add new operators when required.
+ *
+ * |SaturateOp<T>| will saturate at the minimum and maximum values of
+ * type T. If you need other bounds, implement a clamped-type class and
+ * specialize the type traits accordingly.
+ */
+template <typename T>
+class SaturateOp {
+ public:
+ explicit SaturateOp(T& aValue) : mValue(aValue) {
+ // We should actually check for |std::is_scalar<T>::value| to be
+ // true, but this type trait is not available everywhere. Relax
+ // this assertion if you want to use floating point values as well.
+ static_assert(std::is_integral_v<T>,
+ "Integral type required in instantiation");
+ }
+
+ // Add and subtract operators
+
+ T operator+(const T& aRhs) const { return T(mValue) += aRhs; }
+
+ T operator-(const T& aRhs) const { return T(mValue) -= aRhs; }
+
+ // Compound operators
+
+ const T& operator+=(const T& aRhs) const {
+ const T min = std::numeric_limits<T>::min();
+ const T max = std::numeric_limits<T>::max();
+
+ if (aRhs > static_cast<T>(0)) {
+ mValue = (max - aRhs) < mValue ? max : mValue + aRhs;
+ } else {
+ mValue = (min - aRhs) > mValue ? min : mValue + aRhs;
+ }
+ return mValue;
+ }
+
+ const T& operator-=(const T& aRhs) const {
+ const T min = std::numeric_limits<T>::min();
+ const T max = std::numeric_limits<T>::max();
+
+ if (aRhs > static_cast<T>(0)) {
+ mValue = (min + aRhs) > mValue ? min : mValue - aRhs;
+ } else {
+ mValue = (max + aRhs) < mValue ? max : mValue - aRhs;
+ }
+ return mValue;
+ }
+
+ // Increment and decrement operators
+
+ const T& operator++() const // prefix
+ {
+ return operator+=(static_cast<T>(1));
+ }
+
+ T operator++(int) const // postfix
+ {
+ const T value(mValue);
+ operator++();
+ return value;
+ }
+
+ const T& operator--() const // prefix
+ {
+ return operator-=(static_cast<T>(1));
+ }
+
+ T operator--(int) const // postfix
+ {
+ const T value(mValue);
+ operator--();
+ return value;
+ }
+
+ private:
+ SaturateOp(const SaturateOp<T>&) = delete;
+ SaturateOp(SaturateOp<T>&&) = delete;
+ SaturateOp& operator=(const SaturateOp<T>&) = delete;
+ SaturateOp& operator=(SaturateOp<T>&&) = delete;
+
+ T& mValue;
+};
+
+/**
+ * |Saturate<T>| is a value type for saturation arithmetics. It's
+ * built on top of |SaturateOp<T>|.
+ */
+template <typename T>
+class Saturate {
+ public:
+ Saturate() = default;
+ MOZ_IMPLICIT Saturate(const Saturate<T>&) = default;
+
+ MOZ_IMPLICIT Saturate(Saturate<T>&& aValue) {
+ mValue = std::move(aValue.mValue);
+ }
+
+ explicit Saturate(const T& aValue) : mValue(aValue) {}
+
+ const T& value() const { return mValue; }
+
+ // Compare operators
+
+ bool operator==(const Saturate<T>& aRhs) const {
+ return mValue == aRhs.mValue;
+ }
+
+ bool operator!=(const Saturate<T>& aRhs) const { return !operator==(aRhs); }
+
+ bool operator==(const T& aRhs) const { return mValue == aRhs; }
+
+ bool operator!=(const T& aRhs) const { return !operator==(aRhs); }
+
+ // Assignment operators
+
+ Saturate<T>& operator=(const Saturate<T>&) = default;
+
+ Saturate<T>& operator=(Saturate<T>&& aRhs) {
+ mValue = std::move(aRhs.mValue);
+ return *this;
+ }
+
+ // Add and subtract operators
+
+ Saturate<T> operator+(const Saturate<T>& aRhs) const {
+ Saturate<T> lhs(mValue);
+ return lhs += aRhs.mValue;
+ }
+
+ Saturate<T> operator+(const T& aRhs) const {
+ Saturate<T> lhs(mValue);
+ return lhs += aRhs;
+ }
+
+ Saturate<T> operator-(const Saturate<T>& aRhs) const {
+ Saturate<T> lhs(mValue);
+ return lhs -= aRhs.mValue;
+ }
+
+ Saturate<T> operator-(const T& aRhs) const {
+ Saturate<T> lhs(mValue);
+ return lhs -= aRhs;
+ }
+
+ // Compound operators
+
+ Saturate<T>& operator+=(const Saturate<T>& aRhs) {
+ SaturateOp<T>(mValue) += aRhs.mValue;
+ return *this;
+ }
+
+ Saturate<T>& operator+=(const T& aRhs) {
+ SaturateOp<T>(mValue) += aRhs;
+ return *this;
+ }
+
+ Saturate<T>& operator-=(const Saturate<T>& aRhs) {
+ SaturateOp<T>(mValue) -= aRhs.mValue;
+ return *this;
+ }
+
+ Saturate<T>& operator-=(const T& aRhs) {
+ SaturateOp<T>(mValue) -= aRhs;
+ return *this;
+ }
+
+ // Increment and decrement operators
+
+ Saturate<T>& operator++() // prefix
+ {
+ ++SaturateOp<T>(mValue);
+ return *this;
+ }
+
+ Saturate<T> operator++(int) // postfix
+ {
+ return Saturate<T>(SaturateOp<T>(mValue)++);
+ }
+
+ Saturate<T>& operator--() // prefix
+ {
+ --SaturateOp<T>(mValue);
+ return *this;
+ }
+
+ Saturate<T> operator--(int) // postfix
+ {
+ return Saturate<T>(SaturateOp<T>(mValue)--);
+ }
+
+ private:
+ T mValue;
+};
+
+} // namespace detail
+
+typedef detail::Saturate<int8_t> SaturateInt8;
+typedef detail::Saturate<int16_t> SaturateInt16;
+typedef detail::Saturate<int32_t> SaturateInt32;
+typedef detail::Saturate<uint8_t> SaturateUint8;
+typedef detail::Saturate<uint16_t> SaturateUint16;
+typedef detail::Saturate<uint32_t> SaturateUint32;
+
+} // namespace mozilla
+
+template <typename LhsT, typename RhsT>
+bool operator==(LhsT aLhs, const mozilla::detail::Saturate<RhsT>& aRhs) {
+ return aRhs.operator==(static_cast<RhsT>(aLhs));
+}
+
+template <typename LhsT, typename RhsT>
+bool operator!=(LhsT aLhs, const mozilla::detail::Saturate<RhsT>& aRhs) {
+ return !(aLhs == aRhs);
+}
+
+#endif // mozilla_Saturate_h