compiler/alib/reallocvec.c

   1 /*
   2     Copyright © 1995-2003, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: New Exec pendant of ANSI C function realloc() using AllocVec()
   6     Lang: english
   7 */
   8
   9 #define REALLOC_MININCREASE 1024
  10 #define REALLOC_MINDECREASE 4096
  11
  12 /*****************************************************************************
  13
  14     NAME */
  15 #include <proto/exec.h>
  16
  17 //      AROS_LH3(APTR, AllocVec,
  18         APTR ReAllocVec (
  19
  20 /*  SYNOPSIS */
  21         APTR  oldmem,
  22         ULONG newsize,
  23         ULONG requirements)
  24 //      AROS_LHA(APTR,  oldmem,       A0),
  25 //      AROS_LHA(ULONG, byteSize,     D0),
  26 //      AROS_LHA(ULONG, requirements, D1),
  27 /*  SYNOPSIS */
  28 //      struct ExecBase *, SysBase, 1xx, Exec)
  29
  30 /*  FUNCTION
  31         Change the size of an AllocVec:ed part of memory. The memory must
  32         have been allocated by AllocVec(). If you reduce the
  33         size, the old contents will be lost. If you enlarge the size,
  34         the new contents will be undefined.
  35
  36     INPUTS
  37         oldmen - What you got from AllocVec().
  38         newsize - The new size.
  39         requirements - The (new) requirements.
  40                 Note that if no new block of memory is allocated, the
  41                 requirements are not considered.
  42
  43     RESULT
  44         A pointer to the allocated memory or NULL. If you don't need the
  45         memory anymore, you can pass this pointer to FreeVec().
  46
  47     NOTES
  48         If you get NULL, the memory at oldmem will not have been freed and
  49         can still be used.
  50         Note that if no new block of memory is allocated, the requirements
  51         are not considered.
  52
  53         This function must not be used in a shared library or in a
  54         threaded application. (???)
  55
  56
  57     EXAMPLE
  58
  59     BUGS
  60
  61     SEE ALSO
  62         AllocVec(), FreeVec(), CopyMem()
  63
  64     INTERNALS
  65
  66     HISTORY
  67
  68 ******************************************************************************/
  69 {
  70 //    AROS_LIBFUNC_INIT
  71     UBYTE * mem, * newmem;
  72     ULONG oldsize;
  73
  74     if (!oldmem)
  75         return AllocVec (newsize, requirements);
  76
  77     mem = (UBYTE *)oldmem - AROS_ALIGN(sizeof(ULONG));
  78     oldsize = *((ULONG *)mem) - sizeof(ULONG);
  79
  80     /* Reduce or enlarge the memory ? */
  81     if (newsize < oldsize)
  82     {
  83         /* Don't change anything for small changes */
  84         if ((oldsize - newsize) < REALLOC_MINDECREASE)
  85             newmem = oldmem;
  86         else
  87             goto copy;
  88     }
  89     else if (newsize == oldsize) /* Keep the size ? */
  90         newmem = oldmem;
  91     else
  92     {
  93         /* It is likely that if memory is ReAllocVec:ed once it will
  94            be ReAllocVec:ed again, so don't be too stingy with memory */
  95         if ((newsize - oldsize) < REALLOC_MININCREASE)
  96             newsize = oldsize + REALLOC_MININCREASE;
  97 copy:
  98         newmem = AllocVec(newsize, requirements);
  99
 100         if (newmem)
 101         {
 102             CopyMem (oldmem, newmem, newsize);
 103             FreeVec (oldmem);
 104         }
 105     }
 106
 107     return newmem;
 108 //    AROS_LIBFUNC_EXIT
 109 } /* ReAllocVec */