65 lines
1.9 KiB
NASM
65 lines
1.9 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_DIVIDE_H
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#define COMMON_DIVIDE_H
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; ---------------------------------------------------------------------------
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; @routine Utils_Divu16_16_16
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;
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; Divides two unsigned 16 bit values resulting in one 16 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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; R17:R16 = R21:R20 / R23:R22
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; R19:R18 = R21:R20 mod R23:R22
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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 R17:R16 16 bit result
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; @return R19:R18 16 bit remainder
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; @clobbers R25
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Utils_Divu16_16_16:
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mov r16, r20 ; r17:r16=result (intitially: dividend)
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mov r17, r21
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clr r18 ; r19:r18=remainder
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clr r19
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ldi r25, 16 ; 16 bits to divide
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Utils_Divu16_16_16_loop:
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lsl r16 ; shift 0 bit into result
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rol r17
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rol r18
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rol r19
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sub r18, r22 ; try to subtract divisor from value
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sbc r19, r23
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brcs Utils_Divu16_16_16_nofit ; jmp if dividend < divisor
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ori r16, 1 ; otherwise set bit in result
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rjmp Utils_Divu16_16_16_loop_end
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Utils_Divu16_16_16_nofit:
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add r18, r22 ; undo subtraction
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adc r19, r23
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; r17:r16=result
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Utils_Divu16_16_16_loop_end:
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dec r25
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brne Utils_Divu16_16_16_loop
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ret
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; @end
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#endif
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