sat_counter.hh revision 13960:e1ab93677110 
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    /**
60     * Constructor for the counter. The explicit keyword is used to make
61     * sure the user does not assign a number to the counter thinking it
62     * will be used as a counter value when it is in fact used as the number
63     * of bits.
64     *
65     * @param bits How many bits the counter will have.
66     * @param initial_val Starting value for the counter.
67     */
68    explicit SatCounter(unsigned bits, uint8_t initial_val = 0)
69        : initialVal(initial_val), maxVal((1 << bits) - 1),
70          counter(initial_val)
71    {
72        fatal_if(bits > 8*sizeof(uint8_t),
73                 "Number of bits exceeds counter size");
74        fatal_if(initial_val > maxVal,
75                 "Saturating counter's Initial value exceeds max value.");
76    }
77
78    /** Pre-increment operator. */
79    SatCounter&
80    operator++()
81    {
82        if (counter < maxVal) {
83            ++counter;
84        }
85        return *this;
86    }
87
88    /** Post-increment operator. */
89    SatCounter
90    operator++(int)
91    {
92        SatCounter old_counter = *this;
93        ++*this;
94        return old_counter;
95    }
96
97    /** Pre-decrement operator. */
98    SatCounter&
99    operator--()
100    {
101        if (counter > 0) {
102            --counter;
103        }
104        return *this;
105    }
106
107    /** Post-decrement operator. */
108    SatCounter
109    operator--(int)
110    {
111        SatCounter old_counter = *this;
112        --*this;
113        return old_counter;
114    }
115
116    /**
117     * Read the counter's value.
118     */
119    operator uint8_t() const { return counter; }
120
121    /** Reset the counter to its initial value. */
122    void reset() { counter = initialVal; }
123
124  private:
125    uint8_t initialVal;
126    uint8_t maxVal;
127    uint8_t counter;
128};
129
130#endif // __BASE_SAT_COUNTER_HH__
131