compiler/arossupport/calcchecksum.c

   1 /*
   2     Copyright © 1995-2001, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Calculate a checksum for a given area of memory
   6     Lang: english
   7 */
   8
   9 #include <aros/system.h>
  10
  11 /*****************************************************************************
  12
  13     NAME */
  14 #include <proto/arossupport.h>
  15
  16         ULONG CalcChecksum (
  17
  18 /*  SYNOPSIS */
  19         APTR  memory,
  20         ULONG size)
  21
  22 /*  FUNCTION
  23         Calculate a checksum for a given area of memory.
  24
  25     INPUTS
  26         memory - Start here
  27         size - This many bytes. Must be a multiple of sizeof(ULONG)
  28
  29     RESULT
  30         The checksum for the memory. If you store the checksum somewhere
  31         in the area and run CalcChecksum() again, the result will be 0.
  32         To achieve this, you must set the place, where the checksum will
  33         be placed later, to 0 before you call the function.
  34
  35     NOTES
  36         This function is not part of a library and may thus be called
  37         any time.
  38
  39     EXAMPLE
  40         ULONG mem[512];
  41
  42         mem[0] = 0; // Store checksum here
  43         mem[0] = CalcChecksum (mem, sizeof (mem));
  44
  45         if (CalcChecksum (mem, sizeof (mem))
  46             printf ("Something is wrong !!\n");
  47         else
  48             printf ("Data is unchanged.\n");
  49
  50     BUGS
  51
  52     SEE ALSO
  53         exec.library/SumKickData(), exec.library/SumLibrary()
  54
  55     INTERNALS
  56         The function uses the DOS way: sum all the ULONGs and return the
  57         negative result. Not very safe, but then it's quite fast :)
  58
  59     HISTORY
  60         26-10-95    digulla created
  61
  62 ******************************************************************************/
  63 {
  64     ULONG   sum;
  65     ULONG * lptr;
  66
  67     for (sum=0, lptr=(ULONG *)memory; size>0; size-=sizeof(ULONG))
  68         sum += *lptr ++;
  69
  70     return -sum;
  71 } /* CalcChecksum */
  72