sysdeps/m68k/rshift.S

   1 /* mc68020 __mpn_rshift -- Shift right a low-level natural-number integer.
   2
   3 Copyright (C) 1996, 1998 Free Software Foundation, Inc.
   4
   5 This file is part of the GNU MP Library.
   6
   7 The GNU MP Library is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU Lesser General Public License as published by
   9 the Free Software Foundation; either version 2.1 of the License, or (at your
  10 option) any later version.
  11
  12 The GNU MP Library is distributed in the hope that it will be useful, but
  13 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  14 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  15 License for more details.
  16
  17 You should have received a copy of the GNU Lesser General Public License
  18 along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
  19 the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  20 MA 02111-1307, USA. */
  21
  22 /*
  23   INPUT PARAMETERS
  24   res_ptr       (sp + 4)
  25   s_ptr         (sp + 8)
  26   s_size        (sp + 16)
  27   cnt           (sp + 12)
  28 */
  29
  30 #include "sysdep.h"
  31 #include "asm-syntax.h"
  32
  33 #define res_ptr a1
  34 #define s_ptr a0
  35 #define s_size d6
  36 #define cnt d4
  37
  38         TEXT
  39 ENTRY(__mpn_rshift)
  40 /* Save used registers on the stack.  */
  41         moveml  R(d2)-R(d6)/R(a2),MEM_PREDEC(sp)
  42
  43 /* Copy the arguments to registers.  */
  44         movel   MEM_DISP(sp,28),R(res_ptr)
  45         movel   MEM_DISP(sp,32),R(s_ptr)
  46         movel   MEM_DISP(sp,36),R(s_size)
  47         movel   MEM_DISP(sp,40),R(cnt)
  48
  49         moveql  #1,R(d5)
  50         cmpl    R(d5),R(cnt)
  51         bne     L(Lnormal)
  52         cmpl    R(res_ptr),R(s_ptr)
  53         bls     L(Lspecial)             /* jump if res_ptr >= s_ptr */
  54 #if (defined (__mc68020__) || defined (__NeXT__) || defined(mc68020))
  55         lea     MEM_INDX1(res_ptr,s_size,l,4),R(a2)
  56 #else /* not mc68020 */
  57         movel   R(s_size),R(d0)
  58         asll    #2,R(d0)
  59         lea     MEM_INDX(res_ptr,d0,l),R(a2)
  60 #endif
  61         cmpl    R(s_ptr),R(a2)
  62         bls     L(Lspecial)             /* jump if s_ptr >= res_ptr + s_size */
  63
  64 L(Lnormal:)
  65         moveql  #32,R(d5)
  66         subl    R(cnt),R(d5)
  67         movel   MEM_POSTINC(s_ptr),R(d2)
  68         movel   R(d2),R(d0)
  69         lsll    R(d5),R(d0)             /* compute carry limb */
  70
  71         lsrl    R(cnt),R(d2)
  72         movel   R(d2),R(d1)
  73         subql   #1,R(s_size)
  74         beq     L(Lend)
  75         lsrl    #1,R(s_size)
  76         bcs     L(L1)
  77         subql   #1,R(s_size)
  78
  79 L(Loop:)
  80         movel   MEM_POSTINC(s_ptr),R(d2)
  81         movel   R(d2),R(d3)
  82         lsll    R(d5),R(d3)
  83         orl     R(d3),R(d1)
  84         movel   R(d1),MEM_POSTINC(res_ptr)
  85         lsrl    R(cnt),R(d2)
  86 L(L1:)
  87         movel   MEM_POSTINC(s_ptr),R(d1)
  88         movel   R(d1),R(d3)
  89         lsll    R(d5),R(d3)
  90         orl     R(d3),R(d2)
  91         movel   R(d2),MEM_POSTINC(res_ptr)
  92         lsrl    R(cnt),R(d1)
  93
  94         dbf     R(s_size),L(Loop)
  95         subl    #0x10000,R(s_size)
  96         bcc     L(Loop)
  97
  98 L(Lend:)
  99         movel   R(d1),MEM(res_ptr) /* store most significant limb */
 100
 101 /* Restore used registers from stack frame.  */
 102         moveml  MEM_POSTINC(sp),R(d2)-R(d6)/R(a2)
 103         rts
 104
 105 /* We loop from most significant end of the arrays, which is only
 106    permissible if the source and destination don't overlap, since the
 107    function is documented to work for overlapping source and destination.  */
 108
 109 L(Lspecial:)
 110 #if (defined (__mc68020__) || defined (__NeXT__) || defined(mc68020))
 111         lea     MEM_INDX1(s_ptr,s_size,l,4),R(s_ptr)
 112         lea     MEM_INDX1(res_ptr,s_size,l,4),R(res_ptr)
 113 #else /* not mc68000 */
 114         movel   R(s_size),R(d0)
 115         asll    #2,R(d0)
 116         addl    R(s_size),R(s_ptr)
 117         addl    R(s_size),R(res_ptr)
 118 #endif
 119
 120         clrl    R(d0)                   /* initialize carry */
 121         eorw    #1,R(s_size)
 122         lsrl    #1,R(s_size)
 123         bcc     L(LL1)
 124         subql   #1,R(s_size)
 125
 126 L(LLoop:)
 127         movel   MEM_PREDEC(s_ptr),R(d2)
 128         roxrl   #1,R(d2)
 129         movel   R(d2),MEM_PREDEC(res_ptr)
 130 L(LL1:)
 131         movel   MEM_PREDEC(s_ptr),R(d2)
 132         roxrl   #1,R(d2)
 133         movel   R(d2),MEM_PREDEC(res_ptr)
 134
 135         dbf     R(s_size),L(LLoop)
 136         roxrl   #1,R(d0)                /* save cy in msb */
 137         subl    #0x10000,R(s_size)
 138         bcs     L(LLend)
 139         addl    R(d0),R(d0)             /* restore cy */
 140         bra     L(LLoop)
 141
 142 L(LLend:)
 143 /* Restore used registers from stack frame.  */
 144         moveml  MEM_POSTINC(sp),R(d2)-R(d6)/R(a2)
 145         rts
 146 END(__mpn_rshift)