src/base/chunk_generator.hh

   1 /*
   2  * Copyright (c) 2001-2005 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: Steve Reinhardt
  29  */
  30
  31 #ifndef __BASE__CHUNK_GENERATOR_HH__
  32 #define __BASE__CHUNK_GENERATOR_HH__
  33
  34 /**
  35  * @file
  36  * Declaration and inline definition of ChunkGenerator object.
  37  */
  38
  39 #include <algorithm>
  40
  41 #include "base/intmath.hh"
  42 #include "base/types.hh"
  43
  44 /**
  45  * This class takes an arbitrary memory region (address/length pair)
  46  * and generates a series of appropriately (e.g. block- or page-)
  47  * aligned chunks covering the same region.
  48  *
  49  * Example usage:
  50
  51 \code
  52     for (ChunkGenerator gen(addr, size, chunkSize); !gen.done(); gen.next()) {
  53         doSomethingChunky(gen.addr(), gen.size());
  54     }
  55 \endcode
  56  */
  57 class ChunkGenerator
  58 {
  59   private:
  60     /** The starting address of the current chunk. */
  61     Addr curAddr;
  62     /** The starting address of the next chunk (after the current one). */
  63     Addr nextAddr;
  64     /** The size of the current chunk (in bytes). */
  65     unsigned  curSize;
  66     /** The number of bytes remaining in the region after the current chunk. */
  67     unsigned  sizeLeft;
  68     /** The start address so we can calculate offset in writing block. */
  69     const Addr startAddr;
  70     /** The maximum chunk size, e.g., the cache block size or page size. */
  71     const unsigned chunkSize;
  72
  73   public:
  74     /**
  75      * Constructor.
  76      * @param _startAddr The starting address of the region.
  77      * @param totalSize The total size of the region.
  78      * @param _chunkSize The size/alignment of chunks into which
  79      *    the region should be decomposed.
  80      */
  81     ChunkGenerator(Addr _startAddr, unsigned totalSize, unsigned _chunkSize)
  82         : startAddr(_startAddr), chunkSize(_chunkSize)
  83     {
  84         // chunkSize must be a power of two
  85         assert(chunkSize == 0 || isPowerOf2(chunkSize));
  86
  87         // set up initial chunk.
  88         curAddr = startAddr;
  89
  90         if (chunkSize == 0) //Special Case, if we see 0, assume no chuncking
  91         {
  92             nextAddr = startAddr + totalSize;
  93         }
  94         else
  95         {
  96             // nextAddr should be *next* chunk start
  97             nextAddr = roundUp(startAddr, chunkSize);
  98             if (curAddr == nextAddr) {
  99                 // ... even if startAddr is already chunk-aligned
 100                 nextAddr += chunkSize;
 101             }
 102         }
 103
 104         // how many bytes are left between curAddr and the end of this chunk?
 105         unsigned left_in_chunk = nextAddr - curAddr;
 106         curSize = std::min(totalSize, left_in_chunk);
 107         sizeLeft = totalSize - curSize;
 108     }
 109
 110     /** Return starting address of current chunk. */
 111     Addr addr() const { return curAddr; }
 112     /** Return size in bytes of current chunk. */
 113     unsigned size() const { return curSize; }
 114
 115     /** Number of bytes we have already chunked up. */
 116     unsigned complete() const { return curAddr - startAddr; }
 117
 118     /**
 119      * Are we done?  That is, did the last call to next() advance
 120      * past the end of the region?
 121      * @return True if yes, false if more to go.
 122      */
 123     bool done() const { return (curSize == 0); }
 124
 125     /**
 126      * Is this the last chunk?
 127      * @return True if yes, false if more to go.
 128      */
 129     bool last() const { return (sizeLeft == 0); }
 130
 131     /**
 132      * Advance generator to next chunk.
 133      * @return True if successful, false if unsuccessful
 134      * (because we were at the last chunk).
 135      */
 136     bool
 137     next()
 138     {
 139         if (sizeLeft == 0) {
 140             curSize = 0;
 141             return false;
 142         }
 143
 144         curAddr = nextAddr;
 145         curSize = std::min(sizeLeft, chunkSize);
 146         sizeLeft -= curSize;
 147         nextAddr += curSize;
 148         return true;
 149     }
 150 };
 151
 152 #endif // __BASE__CHUNK_GENERATOR_HH__