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227 lines
7.0 KiB
C++
227 lines
7.0 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-*/
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef MOZILLA_TIMEVARYING_H_
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#define MOZILLA_TIMEVARYING_H_
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#include "nsTArray.h"
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namespace mozilla {
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/**
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* This is just for CTOR/DTOR tracking. We can't put this in
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* TimeVarying directly because the different template instances have
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* different sizes and that confuses things.
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*/
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class TimeVaryingBase {
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protected:
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TimeVaryingBase()
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{
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MOZ_COUNT_CTOR(TimeVaryingBase);
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}
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~TimeVaryingBase()
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{
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MOZ_COUNT_DTOR(TimeVaryingBase);
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}
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};
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/**
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* Objects of this class represent values that can change over time ---
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* a mathematical function of time.
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* Time is the type of time values, T is the value that changes over time.
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* There are a finite set of "change times"; at each change time, the function
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* instantly changes to a new value. ReservedChanges should be set to the
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* expected number of change events that the object is likely to contain.
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* This value should be 0 for all consumers unless you know that a higher value
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* would be a benefit.
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* There is also a "current time" which must always advance (not go backward).
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* The function is constant for all times less than the current time.
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* When the current time is advanced, the value of the function at the new
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* current time replaces the values for all previous times.
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*
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* The implementation records a mCurrent (the value at the current time)
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* and an array of "change times" (greater than the current time) and the
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* new value for each change time. This is a simple but dumb implementation.
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*/
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template <typename Time, typename T, uint32_t ReservedChanges>
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class TimeVarying : public TimeVaryingBase {
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public:
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TimeVarying(const T& aInitial) : mCurrent(aInitial) {}
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/**
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* This constructor can only be called if mCurrent has a no-argument
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* constructor.
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*/
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TimeVarying() : mCurrent() {}
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/**
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* Sets the value for all times >= aTime to aValue.
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*/
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void SetAtAndAfter(Time aTime, const T& aValue)
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{
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for (int32_t i = mChanges.Length() - 1; i >= 0; --i) {
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NS_ASSERTION(i == int32_t(mChanges.Length() - 1),
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"Always considering last element of array");
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if (aTime > mChanges[i].mTime) {
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if (mChanges[i].mValue != aValue) {
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mChanges.AppendElement(Entry(aTime, aValue));
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}
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return;
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}
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if (aTime == mChanges[i].mTime) {
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if ((i > 0 ? mChanges[i - 1].mValue : mCurrent) == aValue) {
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mChanges.RemoveElementAt(i);
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return;
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}
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mChanges[i].mValue = aValue;
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return;
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}
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mChanges.RemoveElementAt(i);
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}
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mChanges.InsertElementAt(0, Entry(aTime, aValue));
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}
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/**
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* Returns the final value of the function. If aTime is non-null,
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* sets aTime to the time at which the function changes to that final value.
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* If there are no changes after the current time, returns INT64_MIN in aTime.
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*/
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const T& GetLast(Time* aTime = nullptr) const
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{
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if (mChanges.IsEmpty()) {
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if (aTime) {
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*aTime = INT64_MIN;
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}
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return mCurrent;
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}
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if (aTime) {
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*aTime = mChanges[mChanges.Length() - 1].mTime;
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}
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return mChanges[mChanges.Length() - 1].mValue;
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}
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/**
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* Returns the value of the function just before time aTime.
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*/
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const T& GetBefore(Time aTime) const
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{
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if (mChanges.IsEmpty() || aTime <= mChanges[0].mTime) {
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return mCurrent;
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}
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int32_t changesLength = mChanges.Length();
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if (mChanges[changesLength - 1].mTime < aTime) {
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return mChanges[changesLength - 1].mValue;
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}
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for (uint32_t i = 1; ; ++i) {
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if (aTime <= mChanges[i].mTime) {
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NS_ASSERTION(mChanges[i].mValue != mChanges[i - 1].mValue,
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"Only changed values appear in array");
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return mChanges[i - 1].mValue;
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}
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}
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}
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/**
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* Returns the value of the function at time aTime.
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* If aEnd is non-null, sets *aEnd to the time at which the function will
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* change from the returned value to a new value, or INT64_MAX if that
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* never happens.
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* If aStart is non-null, sets *aStart to the time at which the function
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* changed to the returned value, or INT64_MIN if that happened at or
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* before the current time.
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*
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* Currently uses a linear search, but could use a binary search.
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*/
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const T& GetAt(Time aTime, Time* aEnd = nullptr, Time* aStart = nullptr) const
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{
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if (mChanges.IsEmpty() || aTime < mChanges[0].mTime) {
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if (aStart) {
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*aStart = INT64_MIN;
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}
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if (aEnd) {
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*aEnd = mChanges.IsEmpty() ? INT64_MAX : mChanges[0].mTime;
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}
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return mCurrent;
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}
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int32_t changesLength = mChanges.Length();
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if (mChanges[changesLength - 1].mTime <= aTime) {
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if (aEnd) {
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*aEnd = INT64_MAX;
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}
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if (aStart) {
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*aStart = mChanges[changesLength - 1].mTime;
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}
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return mChanges[changesLength - 1].mValue;
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}
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for (uint32_t i = 1; ; ++i) {
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if (aTime < mChanges[i].mTime) {
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if (aEnd) {
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*aEnd = mChanges[i].mTime;
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}
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if (aStart) {
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*aStart = mChanges[i - 1].mTime;
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}
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NS_ASSERTION(mChanges[i].mValue != mChanges[i - 1].mValue,
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"Only changed values appear in array");
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return mChanges[i - 1].mValue;
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}
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}
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}
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/**
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* Advance the current time to aTime.
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*/
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void AdvanceCurrentTime(Time aTime)
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{
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for (uint32_t i = 0; i < mChanges.Length(); ++i) {
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if (aTime < mChanges[i].mTime) {
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mChanges.RemoveElementsAt(0, i);
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return;
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}
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mCurrent = mChanges[i].mValue;
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}
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mChanges.Clear();
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}
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/**
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* Make all currently pending changes happen aDelta later than their
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* current change times.
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*/
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void InsertTimeAtStart(Time aDelta)
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{
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for (uint32_t i = 0; i < mChanges.Length(); ++i) {
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mChanges[i].mTime += aDelta;
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}
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}
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/**
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* Replace the values of this function at aTimeOffset and later with the
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* values of aOther taken from zero, so if aOther is V at time T >= 0
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* then this function will be V at time T + aTimeOffset. aOther's current
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* time must be >= 0.
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*/
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void Append(const TimeVarying& aOther, Time aTimeOffset)
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{
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NS_ASSERTION(aOther.mChanges.IsEmpty() || aOther.mChanges[0].mTime >= 0,
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"Negative time not allowed here");
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NS_ASSERTION(&aOther != this, "Can't self-append");
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SetAtAndAfter(aTimeOffset, aOther.mCurrent);
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for (uint32_t i = 0; i < aOther.mChanges.Length(); ++i) {
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const Entry& e = aOther.mChanges[i];
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SetAtAndAfter(aTimeOffset + e.mTime, e.mValue);
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}
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}
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private:
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struct Entry {
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Entry(Time aTime, const T& aValue) : mTime(aTime), mValue(aValue) {}
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// The time at which the value changes to mValue
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Time mTime;
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T mValue;
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};
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nsAutoTArray<Entry, ReservedChanges> mChanges;
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T mCurrent;
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};
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}
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#endif /* MOZILLA_TIMEVARYING_H_ */
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