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src/hoard/src/heaplayers/slopheap.h
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00001 // -*- C++ -*-
00002 
00003 /*
00004 
00005 Heap Layers: An Extensible Memory Allocation Infrastructure
00006   
00007 Copyright (C) 2000-2003 by Emery Berger
00008 http://www.cs.umass.edu/~emery
00009 emery@cs.umass.edu
00010   
00011 This program is free software; you can redistribute it and/or modify
00012 it under the terms of the GNU General Public License as published by
00013 the Free Software Foundation; either version 2 of the License, or
00014 (at your option) any later version.
00015   
00016 This program is distributed in the hope that it will be useful,
00017 but WITHOUT ANY WARRANTY; without even the implied warranty of
00018 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00019 GNU General Public License for more details.
00020   
00021 You should have received a copy of the GNU General Public License
00022 along with this program; if not, write to the Free Software
00023 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
00024 
00025 */
00026 
00027 
00028 #ifndef _SLOPHEAP_H_
00029 #define _SLOPHEAP_H_
00030 
00042 namespace HL {
00043   
00044   template <class SuperHeap, int SLOP = 16>
00045   class SlopHeap : public SuperHeap {
00046   public:
00047     SlopHeap (void)
00048       : remaining (0),
00049         ptr (NULL)
00050     {}
00051   
00052     inline void * malloc (const size_t nbytes) {
00053 
00054       // Put the usual case up front.
00055       if (nbytes <= remaining) {
00056         remaining -= nbytes;
00057         char * p = ptr;
00058         ptr += nbytes;
00059         return (void *) p;
00060       }
00061     
00062       //
00063       // We don't have enough space to satisfy the current
00064       // request, so get more memory.
00065       //
00066 
00067       return getMoreMemory(nbytes);
00068     }
00069   
00070     inline void clear (void) {
00071       ptr = NULL;
00072       remaining = 0;
00073       SuperHeap::clear ();
00074     }
00075 
00076     inline void free (void *) {}
00077 
00078   private:
00079 
00080     // Disabled.
00081     inline int remove (void *);
00082 
00083     void * getMoreMemory (size_t nbytes) {
00084       char * newptr = (char *) SuperHeap::malloc (nbytes + SLOP);
00085 
00086       if (newptr == NULL) {
00087         return NULL;
00088       }
00089 
00090       //
00091       // If this new memory is contiguous with the previous one,
00092       // reclaim the "slop".
00093       //
00094     
00095       if ((ptr != NULL) && (ptr + remaining + SLOP == newptr)) {
00096         remaining += SLOP;
00097       } else {
00098         ptr = newptr;
00099         remaining = 0;
00100       }
00101       char * p = ptr;
00102       ptr += nbytes;
00103 
00104       return (void *) p;
00105     }
00106 
00107     char * ptr;
00108     size_t remaining;
00109 
00110   };
00111   
00112 }
00113 
00114 #endif
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