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         APTR ReAllocVec (
  18
  19 /*  SYNOPSIS */
  20         APTR  oldmem,
  21         ULONG newsize,
  22         ULONG requirements)
  23
  24 /*  FUNCTION
  25         Change the size of an AllocVec:ed part of memory. The memory must
  26         have been allocated by AllocVec(). If you reduce the
  27         size, the old contents will be lost. If you enlarge the size,
  28         the new contents will be undefined.
  29
  30     INPUTS
  31         oldmen - What you got from AllocVec().
  32         newsize - The new size.
  33         requirements - The (new) requirements.
  34                 Note that if no new block of memory is allocated, the
  35                 requirements are not considered.
  36
  37     RESULT
  38         A pointer to the allocated memory or NULL. If you don't need the
  39         memory anymore, you can pass this pointer to FreeVec().
  40
  41     NOTES
  42         If you get NULL, the memory at oldmem will not have been freed and
  43         can still be used.
  44         Note that if no new block of memory is allocated, the requirements
  45         are not considered.
  46
  47         This function must not be used in a shared library or in a
  48         threaded application. (???)
  49
  50
  51     EXAMPLE
  52
  53     BUGS
  54
  55     SEE ALSO
  56         exec.library/AllocVec(), exec.library/FreeVec(), exec.library/CopyMem()
  57
  58     INTERNALS
  59
  60     HISTORY
  61
  62 ******************************************************************************/
  63 {
  64 //    AROS_LIBFUNC_INIT
  65     UBYTE * mem, * newmem;
  66     ULONG oldsize;
  67
  68     if (!oldmem)
  69         return AllocVec (newsize, requirements);
  70
  71     mem = (UBYTE *)oldmem - AROS_ALIGN(sizeof(ULONG));
  72     oldsize = *((ULONG *)mem) - sizeof(ULONG);
  73
  74     /* Reduce or enlarge the memory ? */
  75     if (newsize < oldsize)
  76     {
  77         /* Don't change anything for small changes */
  78         if ((oldsize - newsize) < REALLOC_MINDECREASE)
  79             newmem = oldmem;
  80         else
  81             goto copy;
  82     }
  83     else if (newsize == oldsize) /* Keep the size ? */
  84         newmem = oldmem;
  85     else
  86     {
  87         /* It is likely that if memory is ReAllocVec:ed once it will
  88            be ReAllocVec:ed again, so don't be too stingy with memory */
  89         if ((newsize - oldsize) < REALLOC_MININCREASE)
  90             newsize = oldsize + REALLOC_MININCREASE;
  91 copy:
  92         newmem = AllocVec(newsize, requirements);
  93
  94         if (newmem)
  95         {
  96             CopyMem (oldmem, newmem, newsize);
  97             FreeVec (oldmem);
  98         }
  99     }
 100
 101     return newmem;
 102 //    AROS_LIBFUNC_EXIT
 103 } /* ReAllocVec */