src/cpu/pred/sat_counter.hh

   1 /*
   2  * Copyright (c) 2005-2006 The Regents of The University of Michigan
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met: redistributions of source code must retain the above copyright
   8  * notice, this list of conditions and the following disclaimer;
   9  * redistributions in binary form must reproduce the above copyright
  10  * notice, this list of conditions and the following disclaimer in the
  11  * documentation and/or other materials provided with the distribution;
  12  * neither the name of the copyright holders nor the names of its
  13  * contributors may be used to endorse or promote products derived from
  14  * this software without specific prior written permission.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  17  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  18  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  19  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  20  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  21  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  22  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  26  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  *
  28  * Authors: Kevin Lim
  29  */
  30
  31 #ifndef __CPU_PRED_SAT_COUNTER_HH__
  32 #define __CPU_PRED_SAT_COUNTER_HH__
  33
  34 #include "base/logging.hh"
  35 #include "base/types.hh"
  36
  37 /**
  38  * Private counter class for the internal saturating counters.
  39  * Implements an n bit saturating counter and provides methods to
  40  * increment, decrement, and read it.
  41  * @todo Consider making this something that more closely mimics a
  42  * built in class so you can use ++ or --.
  43  */
  44 class SatCounter
  45 {
  46   public:
  47     /**
  48      * Constructor for the counter.
  49      */
  50     SatCounter()
  51         : initialVal(0), counter(0)
  52     { }
  53
  54     /**
  55      * Constructor for the counter.
  56      * @param bits How many bits the counter will have.
  57      */
  58     SatCounter(unsigned bits)
  59         : initialVal(0), maxVal((1 << bits) - 1), counter(0)
  60     { }
  61
  62     /**
  63      * Constructor for the counter.
  64      * @param bits How many bits the counter will have.
  65      * @param initial_val Starting value for each counter.
  66      */
  67     SatCounter(unsigned bits, uint8_t initial_val)
  68         : initialVal(initial_val), maxVal((1 << bits) - 1),
  69           counter(initial_val)
  70     {
  71         // Check to make sure initial value doesn't exceed the max
  72         // counter value.
  73         if (initial_val > maxVal) {
  74             fatal("BP: Initial counter value exceeds max size.");
  75         }
  76     }
  77
  78     /**
  79      * Sets the number of bits.
  80      */
  81     void setBits(unsigned bits) { maxVal = (1 << bits) - 1; }
  82
  83     void reset() { counter = initialVal; }
  84
  85     /**
  86      * Increments the counter's current value.
  87      */
  88     void increment()
  89     {
  90         if (counter < maxVal) {
  91             ++counter;
  92         }
  93     }
  94
  95     /**
  96      * Decrements the counter's current value.
  97      */
  98     void decrement()
  99     {
 100         if (counter > 0) {
 101             --counter;
 102         }
 103     }
 104
 105     /**
 106      * Read the counter's value.
 107      */
 108     uint8_t read() const
 109     { return counter; }
 110
 111   private:
 112     uint8_t initialVal;
 113     uint8_t maxVal;
 114     uint8_t counter;
 115 };
 116
 117 #endif // __CPU_PRED_SAT_COUNTER_HH__