WDL/chunkalloc.h

   1 #ifndef _WDL_CHUNKALLOC_H_
   2 #define _WDL_CHUNKALLOC_H_
   3
   4 #include "wdltypes.h"
   5
   6 class WDL_ChunkAlloc
   7 {
   8   struct _hdr
   9   {
  10     struct _hdr *_next;
  11     char data[16];
  12   };
  13
  14   _hdr *m_chunks;
  15   int m_chunksize, m_chunkused;
  16
  17   public:
  18
  19     WDL_ChunkAlloc(int chunksize=65500) { m_chunks=NULL; m_chunkused=0; m_chunksize=chunksize>16?16:chunksize; }
  20     ~WDL_ChunkAlloc() { Free(); }
  21
  22     void Free()
  23     {
  24       _hdr *a = m_chunks;
  25       m_chunks=0;
  26       m_chunkused=0;
  27       while (a) { _hdr *f=a; a=a->_next; free(f); }
  28     }
  29
  30     void *Alloc(int sz, int align=0)
  31     {
  32       if (sz<1) return NULL;
  33
  34       if (align < 1 || (align & (align-1))) align=1;
  35
  36       if (m_chunks)
  37       {
  38         int use_sz=sz;
  39         char *p = m_chunks->data + m_chunkused;
  40         int a = ((int) (INT_PTR)p) & (align-1);
  41         if (a)
  42         {
  43           use_sz += align-a;
  44           p += align-a;
  45         }
  46         if (use_sz <= m_chunksize - m_chunkused)
  47         {
  48           m_chunkused += use_sz;
  49           return p;
  50         }
  51       }
  52
  53       // we assume that malloc always gives at least 8 byte alignment, and our _next ptr may offset that by 4,
  54       // so no need to allocate extra if less than 4 bytes of alignment requested
  55       int use_align = (align>=4 ? align : 0);
  56       int alloc_sz=sz+use_align;
  57       if (alloc_sz < m_chunksize)
  58       {
  59         // if existing chunk has less free space in it than we would at chunksize, allocate chunksize
  60         if (!m_chunks || m_chunkused > alloc_sz) alloc_sz=m_chunksize;
  61       }
  62       _hdr *nc = (_hdr *)malloc(sizeof(_hdr) + alloc_sz - 16);
  63       if (!nc) return NULL;
  64
  65       int use_sz=sz;
  66       char *ret = nc->data;
  67       int a = ((int) (INT_PTR)ret) & (align-1);
  68       if (a)
  69       {
  70         use_sz += align-a;
  71         ret += align-a;
  72       }
  73
  74       if (m_chunks && (m_chunksize-m_chunkused) >= (alloc_sz - use_sz))
  75       {
  76         // current chunk has as much or more free space than our chunk, put our chunk on the list second
  77         nc->_next = m_chunks->_next;
  78         m_chunks->_next=nc;
  79       }
  80       else
  81       {
  82         // push our chunk to the top of the list
  83         nc->_next = m_chunks;
  84         m_chunks=nc;
  85         m_chunkused = alloc_sz >= m_chunksize ? use_sz : m_chunksize;
  86       }
  87
  88       return ret;
  89     }
  90
  91 };
  92
  93 #endif