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//===------------ mulhi3.S - int16 multiplication -------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// The corresponding C code is something like:
//
// int __mulhi3(int A, int B) {
// int S = 0;
// while (A != 0) {
// if (A & 1)
// S += B;
// A = ((unsigned int) A) >> 1;
// B <<= 1;
// }
// return S;
// }
//
// __mulhi3 has special ABI, as the implementation of libgcc, R25:R24 is used
// to return result, while Rtmp/R21/R22/R23 are clobbered.
//
//===----------------------------------------------------------------------===//
.text
.align 2
#ifdef __AVR_TINY__
.set __tmp_reg__, 16
.set __zero_reg__, 17
#else
.set __tmp_reg__, 0
.set __zero_reg__, 1
#endif
.globl __mulhi3
.type __mulhi3, @function
__mulhi3:
; Use Rzero:Rtmp to store the result.
clr __tmp_reg__
clr __zero_reg__ ; S = 0;
__mulhi3_loop:
clr r21
cp r24, r21
cpc r25, r21
breq __mulhi3_end ; while (A != 0) {
mov r21, r24
andi r21, 1
breq __mulhi3_loop_a ; if (A & 1)
add __tmp_reg__, r22
adc __zero_reg__, r23 ; S += B;
__mulhi3_loop_a:
lsr r25
ror r24 ; A = ((unsigned int) A) >> 1;
lsl r22
rol r23 ; B <<= 1;
rjmp __mulhi3_loop ; }
__mulhi3_end:
; Return the result via R25:R24.
mov r24, __tmp_reg__
mov r25, __zero_reg__
; Restore __zero_reg__ to 0.
clr __zero_reg__
ret ; return S;
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