54 lines
1.4 KiB
ArmAsm
54 lines
1.4 KiB
ArmAsm
//===------------ mulhi3.S - int8 multiplication --------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// The corresponding C code is something like:
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//
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// char __mulqi3(char A, char B) {
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// int S = 0;
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// while (A != 0) {
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// if (A & 1)
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// S += B;
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// B <<= 1;
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// A = ((unsigned char) A) >> 1;
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// }
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// return S;
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// }
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//
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// __mulqi3 has special ABI, as the implementation of libgcc, the result is
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// returned via R24, while Rtmp and R22 are clobbered.
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//
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//===----------------------------------------------------------------------===//
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.text
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.align 2
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#ifdef __AVR_TINY__
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.set __tmp_reg__, 16
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#else
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.set __tmp_reg__, 0
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#endif
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.globl __mulqi3
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.type __mulqi3, @function
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__mulqi3:
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clr __tmp_reg__ ; S = 0;
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__mulqi3_loop:
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cpi r24, 0
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breq __mulqi3_end ; while (A != 0) {
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sbrc r24, 0 ; if (A & 1)
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add __tmp_reg__, r22 ; S += B;
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add r22, r22 ; B <<= 1;
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lsr r24 ; A = ((unsigned char) A) >> 1;
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rjmp __mulqi3_loop ; }
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__mulqi3_end:
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mov r24, __tmp_reg__
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ret ; return S;
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