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/* mc68020 rshift -- Shift right a low-level natural-number integer.
*
* Copyright (C) 1996, 1998, 2001, 2002 Free Software Foundation, Inc.
*
* This file is part of Libgcrypt.
*
* Libgcrypt is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* Libgcrypt 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser 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.
*/
#include "sysdep.h"
#include "asm-syntax.h"
/*******************
* mpi_limb_t
* _gcry_mpih_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(_gcry_mpih_rshift)
C_SYMBOL_NAME(_gcry_mpih_rshift:)
PROLOG(_gcry_mpih_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(_gcry_mpih_rshift)
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