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86 lines
1.4 KiB
ArmAsm
86 lines
1.4 KiB
ArmAsm
;
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; Oliver Schmidt, 2012-10-16
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;
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; unsigned char __fastcall__ _syschdir (const char* name);
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;
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.export __syschdir
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.import curunit, initcwd
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.importzp ptr1, tmp1, tmp2
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;--------------------------------------------------------------------------
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; __syschdir
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.proc __syschdir
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; Save name
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sta ptr1
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stx ptr1+1
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; Process first character
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ldy #0
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lda (ptr1),y
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beq err
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jsr getdigit
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bcs err
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tax
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; Process second character
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iny
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lda (ptr1),y
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beq done
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jsr getdigit
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bcs err
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stx tmp1 ; First digit
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sta tmp2 ; Second digit
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; Multiply first digit by 10
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ldx #8
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@L0: asl
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asl tmp1
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bcc @L1
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clc
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adc #10
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@L1: dex
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bne @L0
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; Add second digit to product
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clc
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adc tmp2
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tax
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; Process third character
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iny
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lda (ptr1),y
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bne err
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; Success, update cwd
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done: stx curunit
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jmp initcwd ; Returns with A = 0
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err: lda #9 ; "Ilegal device"
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rts
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.endproc
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;--------------------------------------------------------------------------
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; getdigit
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.proc getdigit
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sec
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sbc #'0'
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bcs @L0
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sec
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rts
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@L0: cmp #10
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rts
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.endproc |