mirror of
https://github.com/Michaelangel007/apple2_print_uint16.git
synced 2024-12-28 13:30:55 +00:00
91 lines
2.0 KiB
ArmAsm
91 lines
2.0 KiB
ArmAsm
; Michael Pohoreski
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; Optimized from printm
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; Thanks to qkumba for optimizations
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; F8 ROM Entry Points
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COUT = $FDED
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SCRN2 = $F879
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ORG $800
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LDA #$12
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LDX #$34
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JMP PrintUint16
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; Print unsigned 16-bit integer
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; A=High byte
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; X=Low byte
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; Also see: Applesoft LINPRT @ ED24
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; ======================================================================
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PrintUint16
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STX _temp+0
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STA _temp+1
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LDA #0
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STA _bcd+0
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STA _bcd+1
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STA _bcd+2
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Dec2BCD
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LDX #16 ; 16 bits
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SED ; "Double Dabble"
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_Dec2BCD ; https://en.wikipedia.org/wiki/Double_dabble
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ASL _temp+0
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ROL _temp+1
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LDY #$FD ; $00-$FD=-3 bcd[0] bcd[1] bcd[2] bcd[3]
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_DoubleDabble ; Y=FD Y=FE Y=FF Y=00
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LDA _bcd-$FD,Y
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ADC _bcd-$FD,Y
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STA _bcd-$FD,Y
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INY
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BNE _DoubleDabble
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DEX
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BNE _Dec2BCD
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CLD ; X=0 = output length
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DecWidth
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LDY #3 ; maximum 6 digits output
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BCD2Chars
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LDA _bcd-1,Y
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JSR HexA ; print 0, 1, or 2 hex digits
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DEY
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BNE BCD2Chars
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TXA
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CPX #0 ; Handle special case input = $0000 of no output
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BEQ _HaveLeadingDigit
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_PrintDone
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RTS
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; Converts A to high ASCII digits, stores chars in _output
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; @return: A will be bottom nibble in high ASCII
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HexA
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PHA
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JSR SCRN2+2 ; LSR x4 == 0>> 4
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JSR _HexNib
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PLA
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AND #$F
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_HexNib
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BNE _HaveLeadingDigit ; If have leading zero and no output yet ...
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CPX #0 ; ... then skip storing it
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BEQ _HexAsciiDone
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_HaveLeadingDigit
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CMP #$A ; n < 10 ?
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BCC _Hex2Asc
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ADC #6 ; n += 6 $A -> +6 + (C=1) = $11
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_Hex2Asc
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ADC #'0' + $80 ; inverse=remove #$80
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PutChar
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JSR COUT
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INX ; X = output string length
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_HexAsciiDone
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RTS
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_bcd ds 4 ; 6 chars for printing dec
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_temp db 0,0
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