/* mc68020 __mpn_rshift -- Shift right a low-level natural-number integer.

Copyright (C) 1996, 1998 Free Software Foundation, Inc.

This file is part of the GNU MP Library.

The GNU MP Library 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.

The GNU MP Library 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 the GNU MP Library; see the file COPYING.LIB.  If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */

/*
  INPUT PARAMETERS
  res_ptr       (sp + 4)
  s_ptr         (sp + 8)
  s_size        (sp + 16)
  cnt           (sp + 12)
*/

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

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

        TEXT
ENTRY(__mpn_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(Lnormal)
        cmpl    R(res_ptr),R(s_ptr)
        bls     L(Lspecial)             /* 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(Lspecial)             /* jump if s_ptr >= res_ptr + s_size */

L(Lnormal:)
        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(Lend)
        lsrl    #1,R(s_size)
        bcs     L(L1)
        subql   #1,R(s_size)

L(Loop:)
        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(L1:)
        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(Loop)
        subl    #0x10000,R(s_size)
        bcc     L(Loop)

L(Lend:)
        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
   permissible if the source and destination don't overlap, since the
   function is documented to work for overlapping source and destination.  */

L(Lspecial:)
#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(LL1)
        subql   #1,R(s_size)

L(LLoop:)
        movel   MEM_PREDEC(s_ptr),R(d2)
        roxrl   #1,R(d2)
        movel   R(d2),MEM_PREDEC(res_ptr)
L(LL1:)
        movel   MEM_PREDEC(s_ptr),R(d2)
        roxrl   #1,R(d2)
        movel   R(d2),MEM_PREDEC(res_ptr)

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

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