/* mc68020 rshift -- Shift right a low-level natural-number integer.
 *
 *      Copyright (C) 1996, 1998, 2001 Free Software Foundation, Inc.
 *       
 * This file is part of GnuPG.
 *
 * GnuPG is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * GnuPG is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 *
 * Note: This code is heavily based on the GNU MP Library.
 *	 Actually it's the same code with only minor changes in the
 *	 way the data is stored; this is to support the abstraction
 *	 of an optional secure memory allocation which may be used
 *	 to avoid revealing of sensitive data due to paging etc.
 *	 The GNU MP Library itself is published under the LGPL;
 *	 however I decided to publish this code under the plain GPL.
 */


#include "sysdep.h"
#include "asm-syntax.h"


/*******************
 * mpi_limb_t
 * mpihelp_rshift( mpi_ptr_t wp,	(sp + 4)
 *		   mpi_ptr_t up,	(sp + 8)
 *		   mpi_size_t usize,	(sp + 12)
 *		   unsigned cnt)	(sp + 16)
 */

#define res_ptr a1
#define s_ptr a0
#define s_size d6
#define cnt d4

	TEXT
	ALIGN
	GLOBL	C_SYMBOL_NAME(mpihelp_rshift)

C_SYMBOL_NAME(mpihelp_rshift:)
PROLOG(mpihelp_rshift)
	/* Save used registers on the stack.  */
	moveml	R(d2)-R(d6)/R(a2),MEM_PREDEC(sp)

	/* Copy the arguments to registers.  */
	movel	MEM_DISP(sp,28),R(res_ptr)
	movel	MEM_DISP(sp,32),R(s_ptr)
	movel	MEM_DISP(sp,36),R(s_size)
	movel	MEM_DISP(sp,40),R(cnt)

	moveql	#1,R(d5)
	cmpl	R(d5),R(cnt)
	bne	L(Rnormal)
	cmpl	R(res_ptr),R(s_ptr)
	bls	L(Rspecial)		/* jump if res_ptr >= s_ptr */
#if (defined (__mc68020__) || defined (__NeXT__) || defined(mc68020))
	lea	MEM_INDX1(res_ptr,s_size,l,4),R(a2)
#else /* not mc68020 */
	movel	R(s_size),R(d0)
	asll	#2,R(d0)
	lea	MEM_INDX(res_ptr,d0,l),R(a2)
#endif
	cmpl	R(s_ptr),R(a2)
	bls	L(Rspecial)		/* jump if s_ptr >= res_ptr + s_size */

L(Rnormal:)
	moveql	#32,R(d5)
	subl	R(cnt),R(d5)
	movel	MEM_POSTINC(s_ptr),R(d2)
	movel	R(d2),R(d0)
	lsll	R(d5),R(d0)		/* compute carry limb */

	lsrl	R(cnt),R(d2)
	movel	R(d2),R(d1)
	subql	#1,R(s_size)
	beq	L(Rend)
	lsrl	#1,R(s_size)
	bcs	L(R1)
	subql	#1,R(s_size)

L(Roop:)
	movel	MEM_POSTINC(s_ptr),R(d2)
	movel	R(d2),R(d3)
	lsll	R(d5),R(d3)
	orl	R(d3),R(d1)
	movel	R(d1),MEM_POSTINC(res_ptr)
	lsrl	R(cnt),R(d2)
L(R1:)
	movel	MEM_POSTINC(s_ptr),R(d1)
	movel	R(d1),R(d3)
	lsll	R(d5),R(d3)
	orl	R(d3),R(d2)
	movel	R(d2),MEM_POSTINC(res_ptr)
	lsrl	R(cnt),R(d1)

	dbf	R(s_size),L(Roop)
	subl	#0x10000,R(s_size)
	bcc	L(Roop)

L(Rend:)
	movel	R(d1),MEM(res_ptr) /* store most significant limb */

/* Restore used registers from stack frame.  */
	moveml	MEM_POSTINC(sp),R(d2)-R(d6)/R(a2)
	rts

/* We loop from most significant end of the arrays, which is only
   permissable if the source and destination don't overlap, since the
   function is documented to work for overlapping source and destination.  */

L(Rspecial:)
#if (defined (__mc68020__) || defined (__NeXT__) || defined(mc68020))
	lea	MEM_INDX1(s_ptr,s_size,l,4),R(s_ptr)
	lea	MEM_INDX1(res_ptr,s_size,l,4),R(res_ptr)
#else /* not mc68000 */
	movel	R(s_size),R(d0)
	asll	#2,R(d0)
	addl	R(s_size),R(s_ptr)
	addl	R(s_size),R(res_ptr)
#endif

	clrl	R(d0)			/* initialize carry */
	eorw	#1,R(s_size)
	lsrl	#1,R(s_size)
	bcc	L(LR1)
	subql	#1,R(s_size)

L(LRoop:)
	movel	MEM_PREDEC(s_ptr),R(d2)
	roxrl	#1,R(d2)
	movel	R(d2),MEM_PREDEC(res_ptr)
L(LR1:)
	movel	MEM_PREDEC(s_ptr),R(d2)
	roxrl	#1,R(d2)
	movel	R(d2),MEM_PREDEC(res_ptr)

	dbf	R(s_size),L(LRoop)
	roxrl	#1,R(d0)		/* save cy in msb */
	subl	#0x10000,R(s_size)
	bcs	L(LRend)
	addl	R(d0),R(d0)		/* restore cy */
	bra	L(LRoop)

L(LRend:)
/* Restore used registers from stack frame.  */
	moveml	MEM_POSTINC(sp),R(d2)-R(d6)/R(a2)
	rts
EPILOG(mpihelp_rshift)




