1//===------------ mulhi3.S - int16 multiplication -------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// The corresponding C code is something like:
10//
11// int __mulhi3(int A, int B) {
12//   int S = 0;
13//   while (A != 0) {
14//     if (A & 1)
15//       S += B;
16//     A = ((unsigned int) A) >> 1;
17//     B <<= 1;
18//   }
19//   return S;
20// }
21//
22// __mulhi3 has special ABI, as the implementation of libgcc, R25:R24 is used
23// to return result, while Rtmp/R21/R22/R23 are clobbered.
24//
25//===----------------------------------------------------------------------===//
26
27	.text
28	.align 2
29
30#ifdef __AVR_TINY__
31	.set __tmp_reg__, 16
32	.set __zero_reg__, 17
33#else
34	.set __tmp_reg__, 0
35	.set __zero_reg__, 1
36#endif
37
38	.globl __mulhi3
39	.type  __mulhi3, @function
40
41__mulhi3:
42	; Use Rzero:Rtmp to store the result.
43	clr   __tmp_reg__
44	clr   __zero_reg__                 ; S = 0;
45
46__mulhi3_loop:
47	clr   r21
48	cp    r24, r21
49	cpc   r25, r21
50	breq  __mulhi3_end                 ; while (A != 0) {
51
52	mov   r21, r24
53	andi  r21, 1
54	breq  __mulhi3_loop_a              ;   if (A & 1)
55	add   __tmp_reg__, r22
56	adc   __zero_reg__, r23            ;     S += B;
57
58__mulhi3_loop_a:
59	lsr   r25
60	ror   r24                          ;   A = ((unsigned int) A) >> 1;
61	lsl   r22
62	rol   r23                          ;   B <<= 1;
63	rjmp  __mulhi3_loop                ; }
64
65__mulhi3_end:
66	; Return the result via R25:R24.
67	mov   r24, __tmp_reg__
68	mov   r25, __zero_reg__
69	; Restore __zero_reg__ to 0.
70	clr   __zero_reg__
71	ret                                ; return S;
72