chunk_generator.hh revision 6227 
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 */
57class 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        assert(totalSize >= 0);
87
88        // set up initial chunk.
89        curAddr = startAddr;
90
91        if (chunkSize == 0) //Special Case, if we see 0, assume no chuncking
92        {
93            nextAddr = startAddr + totalSize;
94        }
95        else
96        {
97            // nextAddr should be *next* chunk start
98            nextAddr = roundUp(startAddr, chunkSize);
99            if (curAddr == nextAddr) {
100                // ... even if startAddr is already chunk-aligned
101                nextAddr += chunkSize;
102            }
103        }
104
105        // how many bytes are left between curAddr and the end of this chunk?
106        unsigned left_in_chunk = nextAddr - curAddr;
107        curSize = std::min(totalSize, left_in_chunk);
108        sizeLeft = totalSize - curSize;
109    }
110
111    /** Return starting address of current chunk. */
112    Addr addr() const { return curAddr; }
113    /** Return size in bytes of current chunk. */
114    unsigned size() const { return curSize; }
115
116    /** Number of bytes we have already chunked up. */
117    unsigned complete() const { return curAddr - startAddr; }
118
119    /**
120     * Are we done?  That is, did the last call to next() advance
121     * past the end of the region?
122     * @return True if yes, false if more to go.
123     */
124    bool done() const { return (curSize == 0); }
125
126    /**
127     * Advance generator to next chunk.
128     * @return True if successful, false if unsuccessful
129     * (because we were at the last chunk).
130     */
131    bool
132    next()
133    {
134        if (sizeLeft == 0) {
135            curSize = 0;
136            return false;
137        }
138
139        curAddr = nextAddr;
140        curSize = std::min(sizeLeft, chunkSize);
141        sizeLeft -= curSize;
142        nextAddr += curSize;
143        return true;
144    }
145};
146
147#endif // __BASE__CHUNK_GENERATOR_HH__
148