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 #include <assert.h>
  11
  12 /*****************************************************************************
  13
  14     NAME */
  15 #include <proto/arossupport.h>
  16
  17         ULONG CalcChecksum (
  18
  19 /*  SYNOPSIS */
  20         APTR  memory,
  21         ULONG size)
  22
  23 /*  FUNCTION
  24         Calculate a checksum for a given area of memory.
  25
  26     INPUTS
  27         memory - Start here
  28         size - This many bytes. Must be a multiple of sizeof(ULONG)
  29
  30     RESULT
  31         The checksum for the memory. If you store the checksum somewhere
  32         in the area and run CalcChecksum() again, the result will be 0.
  33         To achieve this, you must set the place, where the checksum will
  34         be placed later, to 0 before you call the function.
  35
  36     NOTES
  37         This function is not part of a library and may thus be called
  38         any time.
  39
  40     EXAMPLE
  41         ULONG mem[512];
  42
  43         mem[0] = 0; // Store checksum here
  44         mem[0] = CalcChecksum (mem, sizeof (mem));
  45
  46         if (CalcChecksum (mem, sizeof (mem))
  47             printf ("Something is wrong !!\n");
  48         else
  49             printf ("Data is unchanged.\n");
  50
  51     BUGS
  52
  53     SEE ALSO
  54         exec.library/SumKickData(), exec.library/SumLibrary()
  55
  56     INTERNALS
  57         The function uses the DOS way: sum all the ULONGs and return the
  58         negative result. Not very safe, but then it's quite fast :)
  59
  60     HISTORY
  61         26-10-95    digulla created
  62
  63 ******************************************************************************/
  64 {
  65     ULONG   sum;
  66     ULONG * lptr;
  67
  68     assert (memory);
  69     assert ((size&(sizeof(ULONG)-1))==0);
  70
  71     for (sum=0, lptr=(ULONG *)memory; size>0; size-=sizeof(ULONG))
  72         sum += *lptr ++;
  73
  74     return -sum;
  75 } /* CalcChecksum */
  76