text: /* qud_cksm.c */
  /* Copyright (C) 1993 Eric Young - see README for more details */
  /* From "Message Authentication"  R.R. Jueneman, S.M. Matyas, C.H. Meyer
   * IEEE Communications Magazine Sept 1985 Vol. 23 No. 9 p 29-40
   * This module in only based on the code in this paper and is
   * almost definitely not the same as the MIT implementation.
   */
  #include "des_locl.h"
  
  /* bug fix for dos - 7/6/91 - Larry hughes@logos.ucs.indiana.edu */
  #define B0(a)	(((unsigned long)(a)))
  #define B1(a)	(((unsigned long)(a))<<8)
  #define B2(a)	(((unsigned long)(a))<<16)
  #define B3(a)	(((unsigned long)(a))<<24)
  
  /* used to scramble things a bit */
  /* Got the value MIT uses via brute force :-) 2/10/90 eay */
  #define NOISE	((unsigned long)83653421)
  
  unsigned long des_quad_cksum(input,output,length,out_count,seed)
  des_cblock *input;
  des_cblock *output;
  long length;
  int out_count;
  des_cblock *seed;
  	{
  	unsigned long z0,z1,t0,t1;
  	int i;
  	long l=0;
  	unsigned char *cp;
  	unsigned char *lp;
  
  	if (out_count < 1) out_count=1;
  	lp=(unsigned char *)output;
  
  	z0=B0((*seed)[0])|B1((*seed)[1])|B2((*seed)[2])|B3((*seed)[3]);
  	z1=B0((*seed)[4])|B1((*seed)[5])|B2((*seed)[6])|B3((*seed)[7]);
  
  	for (i=0; ((i<4)&&(i<out_count)); i++)
  		{
  		cp=(unsigned char *)input;
  		l=length;
  		while (l > 0)
  			{
  			if (l > 1)
  				{
  				t0= (unsigned long)(*(cp++));
  				t0|=(unsigned long)B1(*(cp++));
  				l--;
  				}
  			else
  				t0= (unsigned long)(*(cp++));
  			l--;
  			/* add */
  			t0+=z0;
  			t0&=0xffffffff;
  			t1=z1;
  			/* square, well sort of square */
  			z0=((((t0*t0)&0xffffffff)+((t1*t1)&0xffffffff))
  				&0xffffffff)%0x7fffffff; 
  			z1=((t0*((t1+NOISE)&0xffffffff))&0xffffffff)%0x7fffffff;
  			}
  		if (lp != NULL)
  			{
  			/* I believe I finally have things worked out.
  			 * The MIT library assumes that the checksum
  			 * is one huge number and it is returned in a
  			 * host dependant byte order.
  			 */
  			static unsigned long l=1;
  			static unsigned char *c=(unsigned char *)&l;
  
  			if (c[0])
  				{
  				l2c(z0,lp);
  				l2c(z1,lp);
  				}
  			else
  				{
  				lp=output[out_count-i-1];
  				l2n(z1,lp);
  				l2n(z0,lp);
  				}
  			}
  		}
  	return(z0);
  	}
  
  