--- /dev/null
+; Copyright (C) 2017 Free Software Foundation, Inc.
+; Contributed by Sebastian Perta.
+;
+; This file 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 3, or (at your option) any
+; later version.
+;
+; This file 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.
+;
+; Under Section 7 of GPL version 3, you are granted additional
+; permissions described in the GCC Runtime Library Exception, version
+; 3.1, as published by the Free Software Foundation.
+;
+; You should have received a copy of the GNU General Public License and
+; a copy of the GCC Runtime Library Exception along with this program;
+; see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
+; <http://www.gnu.org/licenses/>.
+
+
+#include "vregs.h"
+
+ .text
+
+START_FUNC ___adddi3
+
+ movw hl, sp ; use HL-based addressing (allows for direct addw)
+
+ movw ax, [hl+4]
+ addw ax, [hl+12]
+ movw r8, ax
+
+ mov a, [hl+6] ; middle bytes of the result are determined using 8-bit
+ addc a, [hl+14] ; ADDC insns which both account for and update the carry bit
+ mov r10, a ; (no ADDWC instruction is available)
+ mov a, [hl+7]
+ addc a, [hl+15]
+ mov r11, a
+
+ mov a, [hl+8]
+ addc a, [hl+16]
+ mov r12, a
+ mov a, [hl+9]
+ addc a, [hl+17]
+ mov r13, a
+
+ movw ax, [hl+10]
+ sknc ; account for the possible carry from the
+ incw ax ; latest 8-bit operation
+ addw ax, [hl+18]
+ movw r14, ax
+
+ ret
+
+END_FUNC ___adddi3