sat_counter.hh revision 14210 
1/*
2 * Copyright (c) 2019 Inria
3 * All rights reserved.
4 *
5 * The license below extends only to copyright in the software and shall
6 * not be construed as granting a license to any other intellectual
7 * property including but not limited to intellectual property relating
8 * to a hardware implementation of the functionality of the software
9 * licensed hereunder.  You may use the software subject to the license
10 * terms below provided that you ensure that this notice is replicated
11 * unmodified and in its entirety in all distributions of the software,
12 * modified or unmodified, in source code or in binary form.
13 *
14 * Copyright (c) 2005-2006 The Regents of The University of Michigan
15 * All rights reserved.
16 *
17 * Redistribution and use in source and binary forms, with or without
18 * modification, are permitted provided that the following conditions are
19 * met: redistributions of source code must retain the above copyright
20 * notice, this list of conditions and the following disclaimer;
21 * redistributions in binary form must reproduce the above copyright
22 * notice, this list of conditions and the following disclaimer in the
23 * documentation and/or other materials provided with the distribution;
24 * neither the name of the copyright holders nor the names of its
25 * contributors may be used to endorse or promote products derived from
26 * this software without specific prior written permission.
27 *
28 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
29 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
30 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
31 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
32 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
33 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
34 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
35 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
36 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
37 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
38 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
39 *
40 * Authors: Kevin Lim
41 *          Daniel Carvalho
42 */
43
44#ifndef __BASE_SAT_COUNTER_HH__
45#define __BASE_SAT_COUNTER_HH__
46
47#include <cstdint>
48
49#include "base/logging.hh"
50#include "base/types.hh"
51
52/**
53 * Implements an n bit saturating counter and provides methods to
54 * increment, decrement, and read it.
55 */
56class SatCounter
57{
58  public:
59    /** The default constructor should never be used. */
60    SatCounter() = delete;
61
62    /**
63     * Constructor for the counter. The explicit keyword is used to make
64     * sure the user does not assign a number to the counter thinking it
65     * will be used as a counter value when it is in fact used as the number
66     * of bits.
67     *
68     * @param bits How many bits the counter will have.
69     * @param initial_val Starting value for the counter.
70     */
71    explicit SatCounter(unsigned bits, uint8_t initial_val = 0)
72        : initialVal(initial_val), maxVal((1 << bits) - 1),
73          counter(initial_val)
74    {
75        fatal_if(bits > 8*sizeof(uint8_t),
76                 "Number of bits exceeds counter size");
77        fatal_if(initial_val > maxVal,
78                 "Saturating counter's Initial value exceeds max value.");
79    }
80
81    /** Copy constructor. */
82    SatCounter(const SatCounter& other)
83        : initialVal(other.initialVal), maxVal(other.maxVal),
84          counter(other.counter)
85    {
86    }
87
88    /** Copy assignment. */
89    SatCounter& operator=(const SatCounter& other) {
90        if (this != &other) {
91            SatCounter temp(other);
92            this->swap(temp);
93        }
94        return *this;
95    }
96
97    /** Move constructor. */
98    SatCounter(SatCounter&& other)
99    {
100        initialVal = other.initialVal;
101        maxVal = other.maxVal;
102        counter = other.counter;
103        SatCounter temp(0);
104        other.swap(temp);
105    }
106
107    /** Move assignment. */
108    SatCounter& operator=(SatCounter&& other) {
109        if (this != &other) {
110            initialVal = other.initialVal;
111            maxVal = other.maxVal;
112            counter = other.counter;
113            SatCounter temp(0);
114            other.swap(temp);
115        }
116        return *this;
117    }
118
119    /**
120     * Swap the contents of every member of the class. Used for the default
121     * copy-assignment created by the compiler.
122     *
123     * @param other The other object to swap contents with.
124     */
125    void
126    swap(SatCounter& other)
127    {
128        std::swap(initialVal, other.initialVal);
129        std::swap(maxVal, other.maxVal);
130        std::swap(counter, other.counter);
131    }
132
133    /** Pre-increment operator. */
134    SatCounter&
135    operator++()
136    {
137        if (counter < maxVal) {
138            ++counter;
139        }
140        return *this;
141    }
142
143    /** Post-increment operator. */
144    SatCounter
145    operator++(int)
146    {
147        SatCounter old_counter = *this;
148        ++*this;
149        return old_counter;
150    }
151
152    /** Pre-decrement operator. */
153    SatCounter&
154    operator--()
155    {
156        if (counter > 0) {
157            --counter;
158        }
159        return *this;
160    }
161
162    /** Post-decrement operator. */
163    SatCounter
164    operator--(int)
165    {
166        SatCounter old_counter = *this;
167        --*this;
168        return old_counter;
169    }
170
171    /** Shift-right-assignment. */
172    SatCounter&
173    operator>>=(const int& shift)
174    {
175        this->counter >>= shift;
176        return *this;
177    }
178
179    /** Shift-left-assignment. */
180    SatCounter&
181    operator<<=(const int& shift)
182    {
183        this->counter <<= shift;
184        if (this->counter > maxVal) {
185            this->counter = maxVal;
186        }
187        return *this;
188    }
189
190    /** Add-assignment. */
191    SatCounter&
192    operator+=(const int& value)
193    {
194        if (maxVal - this->counter >= value) {
195            this->counter += value;
196        } else {
197            this->counter = maxVal;
198        }
199        return *this;
200    }
201
202    /** Subtract-assignment. */
203    SatCounter&
204    operator-=(const int& value)
205    {
206        if (this->counter > value) {
207            this->counter -= value;
208        } else {
209            this->counter = 0;
210        }
211        return *this;
212    }
213
214    /**
215     * Read the counter's value.
216     */
217    operator uint8_t() const { return counter; }
218
219    /** Reset the counter to its initial value. */
220    void reset() { counter = initialVal; }
221
222    /**
223     * Calculate saturation percentile of the current counter's value
224     * with regard to its maximum possible value.
225     *
226     * @return A value between 0.0 and 1.0 to indicate which percentile of
227     *         the maximum value the current value is.
228     */
229    double calcSaturation() const { return (double) counter / maxVal; }
230
231    /**
232     * Whether the counter has achieved its maximum value or not.
233     *
234     * @return True if the counter saturated.
235     */
236    bool isSaturated() const { return counter == maxVal; }
237
238    /**
239     * Saturate the counter.
240     *
241     * @return The value added to the counter to reach saturation.
242     */
243    uint8_t saturate()
244    {
245        const uint8_t diff = maxVal - counter;
246        counter = maxVal;
247        return diff;
248    }
249
250  private:
251    uint8_t initialVal;
252    uint8_t maxVal;
253    uint8_t counter;
254};
255
256#endif // __BASE_SAT_COUNTER_HH__
257