cshift.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。

/*
 *  SecuDE Release 4.1 (GMD)
 */
/********************************************************************
 * 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.                *
 *                                                                  *
 ********************************************************************/

/*
 *	shift(OPa,exp2b,result)
 */


#include "arithmetic.h"


void	_shift(A,exp2b,S)
L_NUMBER	A[],S[];
int		exp2b;
{
	register	int wordshift;
	register	int bitshift;
	register	int left = exp2b>0;
	register	int right = exp2b<0;
	register L_NUMBER   cnt;
	register L_NUMBER   *Ap;
	register L_NUMBER   *Sp;
	register 	int WLmBITS;
	register L_NUMBER	dH;
	register L_NUMBER	dL;

	if (right){
		bitshift = (-exp2b) & (WLNG-1);	WLmBITS = WLNG - bitshift;
		wordshift = (-exp2b) >>SWBITS;

		cnt = lngofln(A) - wordshift;
		if (cnt<=0) { lngofln(S) = 0; return; }

		Sp = S;
		Ap = A + wordshift;
		lngofln(S) = cnt;
		dH = dL = *++Ap;
		for ( ; cnt>1 ; cnt-- ) {
			dH = *++Ap;
			if(bitshift){
				*++Sp = (dH<<WLmBITS) | (dL>>bitshift);
				dL = dH;
			} else	*++Sp = dH;
		}

		dH >>= bitshift;
		if (dH) *++Sp = dH;
		else	lngofln(S)--;

		return;
	}

	if (left) {
		cnt = lngofln(A);
		bitshift = (exp2b) & (WLNG-1);	WLmBITS = WLNG - bitshift;
		wordshift = (exp2b) >>SWBITS;

		lngofln(S) = wordshift + cnt;
		Sp = S + lngofln(S);
		Ap = A + cnt;
		dH = dL = *Ap;
/* sparc arch can't handle shifs with word length !!! */
		if (bitshift) {
			if (dL >>= WLmBITS){ lngofln(S)++; *(Sp+1) = dL; }
		}
		else    dL = 0;

		for( ; cnt>1; cnt--){
			dL = *--Ap;
			if(bitshift)
				*Sp-- = (dH<<bitshift) | (dL>>WLmBITS);
			else	*Sp-- = dH;
			dH = dL;
		}
		*Sp-- = dH<<bitshift;

		for( ; Sp > S; Sp--) *Sp = 0;

		return;
	}

	trans(A,S); 
	return;
}