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/*
;-------------------------------------------------------------------------
; CKSUM.A51
;
; This computes the internet checksum on an 8051
;
; Call from C program: UINT cksum(UCHAR xdata * buf, UINT length);
; Where * buf is pointer to first char (must be in xdata space)
; and "length" is number of bytes (not words) to sum over
;-------------------------------------------------------------------------
*/
#include "net.h"
UINT cksum(UCHAR xdata *check,UINT length)
{
LONG sum=0;
UINT i;
UINT xdata *ptr;
ptr=(UINT xdata *)check;
for (i=0;i<(length)/2;i++)
{
sum+=*ptr++;
}
if (length&0x01)
{
sum=sum+((*ptr)&0xff00);
}
sum=(sum&0xffff)+((sum>>16)&0xffff);
if(sum&0xffff0000)
{
sum++;
}
return ( (UINT)((sum)&0xffff));
// return ( (UINT)(~((sum)&0xffff)));
}
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