\ ========== Copyright Header Begin ==========================================
\ 
\ Hypervisor Software File: occhksum.fth
\ 
\ Copyright (c) 2006 Sun Microsystems, Inc. All Rights Reserved.
\ 
\  - Do no alter or remove copyright notices
\ 
\  - Redistribution and use of this software in source and binary forms, with 
\    or without modification, are permitted provided that the following 
\    conditions are met: 
\ 
\  - Redistribution of source code must retain the above copyright notice, 
\    this list of conditions and the following disclaimer.
\ 
\  - Redistribution in binary form must reproduce the above copyright notice,
\    this list of conditions and the following disclaimer in the
\    documentation and/or other materials provided with the distribution. 
\ 
\    Neither the name of Sun Microsystems, Inc. or the names of contributors 
\ may be used to endorse or promote products derived from this software 
\ without specific prior written permission. 
\ 
\     This software is provided "AS IS," without a warranty of any kind. 
\ ALL EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, 
\ INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A 
\ PARTICULAR PURPOSE OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN 
\ MICROSYSTEMS, INC. ("SUN") AND ITS LICENSORS SHALL NOT BE LIABLE FOR 
\ ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR 
\ DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES. IN NO EVENT WILL SUN 
\ OR ITS LICENSORS BE LIABLE FOR ANY LOST REVENUE, PROFIT OR DATA, OR 
\ FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE 
\ DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY, 
\ ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE, EVEN IF 
\ SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
\ 
\ You acknowledge that this software is not designed, licensed or
\ intended for use in the design, construction, operation or maintenance of
\ any nuclear facility. 
\ 
\ ========== Copyright Header End ============================================
id: @(#)occhksum.fth 2.13 99/01/05
purpose: Internet checksum (one's complement of 16-bit words)
copyright: Copyright 1990-1997 Sun Microsystems, Inc.  All Rights Reserved

\ Generate the ones complement checksum of count 16-bit words
\ starting at addr.

headerless
\ Assumes that the buffer is not so long that the high word can overflow
: (oc-checksum) ( accumulator addr count -- checksum )
   2dup + >r  bounds  do  i  be-w@ +  /w  +loop  ( current checksum)
   \ Subtract the extra byte at the end
   r> dup  1 and  if  c@  -  else  drop  then
;

: oc-checksum  ( accumulator addr count -- checksum )
   (oc-checksum)                       ( checksum' )
   lwsplit + lwsplit +                 ( checksum" )
   invert  h# 0.ffff and               ( checksum )
   \ Return ffff if the checksum is 0
   ?dup 0=  if  h# 0.ffff  then        ( checksum )
;
headers