61 lines
1.7 KiB
NASM
61 lines
1.7 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_DIVIDE8_H
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#define COMMON_DIVIDE8_H
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; ---------------------------------------------------------------------------
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; @routine Utils_Divu8_8_8
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;
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; Divides two unsigned 8 bit values resulting in one 8 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 divisions with pen and paper.
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;
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; R16 = R18 / R19
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; R17 = R18 mod R19
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; TODO: adapt for signed values
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;
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; @param R18 8 bit value A
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; @param R19 8 bit value B
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; @return R16 8 bit result
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; @return R17 8 bit remainder
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; @clobbers R25
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Utils_Divu8_8_8:
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mov r16, r18 ; r16=result (intitially: dividend)
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clr r17 ; r17=remainder
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ldi r25, 8 ; 8 bits to divide
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Utils_Divu8_8_8_loop:
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lsl r16 ; shift 0 bit into result
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rol r17
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sub r17, r19 ; try to subtract divisor from value
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brcs Utils_Divu8_8_8_nofit ; jmp if dividend < divisor
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ori r16, 1 ; otherwise set bit in result
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rjmp Utils_Divu8_8_8_loop_end
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Utils_Divu8_8_8_nofit:
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add r17, r19 ; undo subtraction
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; r16=result
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Utils_Divu8_8_8_loop_end:
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dec r25
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brne Utils_Divu8_8_8_loop
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ret
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; @end
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#endif
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