sub.c

SecuDe是一个由安全应用程序接口组成,对验证机制、证件处理、PEM、X.400报文处理和密钥管理提供支持。SecuDe提供DES、 RSA杂凑函数、密钥生成以及数字签名的生成和核实等多种密码机制。

/********************************************************************
 * Copyright (C) 1991, GMD. All rights reserved.                    *
 *                                                                  *
 *                                                                  *
 *                         NOTICE                                   *
 *                                                                  *
 *    Acquisition, use, and distribution of this module             *
 *    and related materials are subject to restrictions             *
 *    mentioned in each volume of the documentation.                *
 *                                                                  *
 ********************************************************************/

/*
 *	L_NUMBER subtraction

 *
 */
 
#include	"arithmetic.h"

/*	A - B	*/
void _sub(Ap,Bp,Diff)
register L_NUMBER *Ap, *Bp, *Diff;
{
	register L_NUMBER	*opA = Ap, *Dp = Diff;
	register int	cnt, carry = 1;
	int	residual;

	if (lngofln(Ap)<lngofln(Bp)) ALU_exception(carry);
	
	cnt = lngofln(Bp); residual = lngofln(Ap) - lngofln(Bp);
	
	for ( ; cnt > 0; cnt--)
		carry = cadd( *++Ap, ~(*++Bp), ++Diff, carry );
		
	for(  ; !carry && (residual>0); residual-- )
		carry = cadd( *++Ap, ~(0), ++Diff, 0 );

	if(Diff != Ap)  for(  ; residual>0 ; residual-- )  *++Diff = *++Ap;

	if (carry) /* OK */;
	else	ALU_exception(carry);
	
	cnt = lngofln(opA);
	Diff = Dp + cnt;
	for (; (Diff>Dp) && !*Diff; Diff--) cnt--;

	lngofln(Dp) = cnt;
	
	return;
}