| 1 | //===------------ mulhi3.S - int8 multiplication --------------------------===// |
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| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | // |
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| 9 | // The corresponding C code is something like: |
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| 10 | // |
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| 11 | // char __mulqi3(char A, char B) { |
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| 12 | // int S = 0; |
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| 13 | // while (A != 0) { |
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| 14 | // if (A & 1) |
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| 15 | // S += B; |
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| 16 | // B <<= 1; |
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| 17 | // A = ((unsigned char) A) >> 1; |
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| 18 | // } |
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| 19 | // return S; |
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| 20 | // } |
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| 21 | // |
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| 22 | // __mulqi3 has special ABI, as the implementation of libgcc, the result is |
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| 23 | // returned via R24, while Rtmp and R22 are clobbered. |
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| 24 | // |
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| 25 | //===----------------------------------------------------------------------===// |
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| 26 | |
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| 27 | .text |
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| 28 | .align 2 |
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| 29 | |
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| 30 | #ifdef __AVR_TINY__ |
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| 31 | .set __tmp_reg__, 16 |
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| 32 | #else |
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| 33 | .set __tmp_reg__, 0 |
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| 34 | #endif |
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| 35 | |
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| 36 | .globl __mulqi3 |
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| 37 | .type __mulqi3, @function |
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| 38 | |
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| 39 | __mulqi3: |
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| 40 | clr __tmp_reg__ ; S = 0; |
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| 41 | |
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| 42 | __mulqi3_loop: |
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| 43 | cpi r24, 0 |
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| 44 | breq __mulqi3_end ; while (A != 0) { |
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| 45 | sbrc r24, 0 ; if (A & 1) |
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| 46 | add __tmp_reg__, r22 ; S += B; |
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| 47 | add r22, r22 ; B <<= 1; |
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| 48 | lsr r24 ; A = ((unsigned char) A) >> 1; |
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| 49 | rjmp __mulqi3_loop ; } |
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| 50 | |
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| 51 | __mulqi3_end: |
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| 52 | mov r24, __tmp_reg__ |
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| 53 | ret ; return S; |
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| 54 | |
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