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diff --git a/ports/sysdeps/m68k/m680x0/add_n.S b/ports/sysdeps/m68k/m680x0/add_n.S
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+/* mc68020 __mpn_add_n -- Add two limb vectors of the same length > 0 and store
+ sum in a third limb vector.
+
+Copyright (C) 1992, 1994, 1996, 1998, 2012 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. If not, see <http://www.gnu.org/licenses/>. */
+
+/*
+ INPUT PARAMETERS
+ res_ptr (sp + 4)
+ s1_ptr (sp + 8)
+ s2_ptr (sp + 16)
+ size (sp + 12)
+*/
+
+#include "sysdep.h"
+#include "asm-syntax.h"
+
+ TEXT
+ENTRY(__mpn_add_n)
+/* Save used registers on the stack. */
+ movel R(d2),MEM_PREDEC(sp)
+ cfi_adjust_cfa_offset (4)
+ movel R(a2),MEM_PREDEC(sp)
+ cfi_adjust_cfa_offset (4)
+ cfi_rel_offset (R(d2), 4)
+ cfi_rel_offset (R(a2), 0)
+
+/* Copy the arguments to registers. Better use movem? */
+ movel MEM_DISP(sp,12),R(a2)
+ movel MEM_DISP(sp,16),R(a0)
+ movel MEM_DISP(sp,20),R(a1)
+ movel MEM_DISP(sp,24),R(d2)
+
+ eorw #1,R(d2)
+ lsrl #1,R(d2)
+ bcc L(L1)
+ subql #1,R(d2) /* clears cy as side effect */
+
+L(Loop:)
+ movel MEM_POSTINC(a0),R(d0)
+ movel MEM_POSTINC(a1),R(d1)
+ addxl R(d1),R(d0)
+ movel R(d0),MEM_POSTINC(a2)
+L(L1:) movel MEM_POSTINC(a0),R(d0)
+ movel MEM_POSTINC(a1),R(d1)
+ addxl R(d1),R(d0)
+ movel R(d0),MEM_POSTINC(a2)
+
+ dbf R(d2),L(Loop) /* loop until 16 lsb of %4 == -1 */
+ subxl R(d0),R(d0) /* d0 <= -cy; save cy as 0 or -1 in d0 */
+ subl #0x10000,R(d2)
+ bcs L(L2)
+ addl R(d0),R(d0) /* restore cy */
+ bra L(Loop)
+
+L(L2:)
+ negl R(d0)
+
+/* Restore used registers from stack frame. */
+ movel MEM_POSTINC(sp),R(a2)
+ cfi_adjust_cfa_offset (-4)
+ cfi_restore (R(a2))
+ movel MEM_POSTINC(sp),R(d2)
+ cfi_adjust_cfa_offset (-4)
+ cfi_restore (R(d2))
+
+ rts
+END(__mpn_add_n)