70 lines
1.8 KiB
NASM
70 lines
1.8 KiB
NASM
; ***************************************************************************
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; copyright : (C) 2025 by Martin Preuss
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; email : martin@libchipcard.de
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;
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; ***************************************************************************
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; * This file is part of the project "AqHome". *
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; * Please see toplevel file COPYING of that project for license details. *
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; ***************************************************************************
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#ifndef COMMON_MULTIPLY_H
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#define COMMON_MULTIPLY_H
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; ---------------------------------------------------------------------------
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; @routine Utils_Mulu16x16_32
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;
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; Multiplies two unsigned 16 bit values resulting in one 32 bit value.
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; This is a rather simple but reasonable fast routine working just like you would
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; when doing multiplications with pen and paper.
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;
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; R19:R18:R17:R16 = R21:R20 * R23:R22
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;
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; TODO: adapt for signed values
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;
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; @param R21:R20 16 bit value A
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; @param R23:R22 16 bit value B
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; @return R19:R18:R17:R16 32 bit result
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; @clobbers R16, R17, R18, R19, R20, R21, R22, R23, R24, R25, R26
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Utils_Mulu16x16_32:
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clr r19
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clr r18
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clr r17
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clr r16
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clr r25
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clr r24
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ldi r26, 16 ; 16 bit multiplicator
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Utils_Mulu16x16_32_loop:
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lsr r23
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ror r22
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brcc Utils_Mulu16x16_32_noadd ; current digit in B is 0, don't add shifted A to result
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add r16, r22
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adc r17, r23
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adc r18, r24
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adc r19, r25
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; brcs Utils_Mulu16x16_32_overflow ; can't happen
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Utils_Mulu16x16_32_noadd:
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dec r26
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breq Utils_Mulu16x16_32_done
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lsl r20
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rol r21
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rol r24
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rol r25
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; brcs Utils_Mulu16x16_32_overflow ; can't happen
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rjmp Utils_Mulu16x16_32_loop
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Utils_Mulu16x16_32_done:
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clc
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ret
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;Utils_Mulu16x16_32_overflow: ; never reached. Multiplying 2 16 bit values can't overflow 32 bit
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; sec
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; ret
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; @end
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#endif ; COMMON_MULTIPLY_H
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