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C02/include/old/stdlib.asm

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2018-01-28 18:30:49 +00:00
; C02 library stdlib.h02 assembly language subroutines
; Requires
; external zero page locations strlo and strhi
; and external locations random, temp0, and temp1.
;Return Absolute Value of Accumulator
abs: CMP #$80 ;If Negative (High Bit Set)
BCC absx ; Carry will Already be Set
EOR #$FF ; One's Complement
ADC #$00 ; and Increment (Carry set by CMP)
absx: RTS
;Multiply A times Y
;Uses temp0, temp1
;Affects A,N,Z,C
mult: STA temp0 ;Store Multiplicand
STY temp1 ;Store Multiplier
;Multiply temp0 times temp1
multt: LDA #$00 ;Initialize Accumulator
BEQ multe ;Enter Loop
multa: CLC
ADC temp0 ;Add Multiplicand
multl: ASL temp0 ;Shift Multiplicand Left
multe: LSR temp1 ;Shift Multiplier Right
BCS multa ;If Bit Shifted Out, Add Multiplicand
BNE multl ;Loop if Any 1 Bits Left
RTS
;Divide A by Y
;Used temp0,temp1
;Affects A,X,N,Z,C
div: STA temp0 ;Store Dividend
STY temp1 ;Store Divisor
;Divide temp0 by temp1
divt: LDA #$00 ;Clear Accumulator
LDX #$07 ;Load Loop Counter
CLC
divl: ROL temp0 ;Shift Bit Out of Dividend
ROL ; into Accumulator
CMP temp1 ;If Accumulator
BCC divs ; >= Divisor
SBC temp1 ;Subtract Divisor
divs: DEX ;Decrement Counter
BPL divl ; and Loop
ROL temp0 ;Shift Result into Dividend
LDA temp0 ;Load Result into Accumulator
RTS
;Generate Pseudo-Random Number
;Uses random
;Affects A,N,Z,C
rand: LDA random ;Load Last Result
BNE randl ;If Zero
ADC #$01 ; Set to 1
randl: ASL ;Shift the Seed
BCC randx ;If a one was shifted out
EOR #$1D ; Twiddle the bite
randx: STA random ;Save the Seed
RTS
;Seed Pseudo-Random Number Generator
rands: STA random ;Store Seed
RTS
;Convert ASCII to Byte
;Uses temp0, temp1
;Affects A,X,Y,N,Z,C
atoc: STX strlo ;Save String Pointer
STY strhi
LDY #$00 ;Initialize Index Into String
STY temp0 ;Initialize Result
atocl: LDA (strlo),Y ;Get Next Character
CMP #$30 ;If Less Than '0'
BCC atocx ; Exit
CMP #$3A ;If Greater Than '9'
BCS atocx ; Exit
AND #$0F ;Convert to Binary Nybble
STA temp1 ; and Save It
LDA temp0 ;Load Result
ASL ;Multiply by 5 by
ASL ; Multiplying by 4
ADC temp0 ; And Adding Itself
ASL ;Multiply that by 2
ADC temp1 ;Add Saved Nybble
STA temp0 ; and Store Result
INY ;Increment Index
BPL atocl ; and Loop
atocx: LDA temp0 ;Load Result
RTS ;And Return
;Convert Byte to ASCII
;Uses strlo, strhi, temp0, temp1, temp2
;Affects A,X,Y,N,Z
ctoa: STX strlo ;Save Pointer in Store Index
STY strhi
JSR cvbcd ;Convert Accumulator to BCD
LDY #$00 ;Set String Offset to 0
LDA temp2 ;Get High Byte
BEQ ctoa1 ;If Not Zero
JSR ntoa ; Convert Low Nybble
ctoa1: LDA temp1 ;Get Low Byte
LSR ;Shift High Nybble
LSR ; into Low Nybble
LSR
LSR
BNE ctoa2 ;If Not Zero
CMP temp2 ; and High Byte
BEQ ctoa3 ; not Zero
ctoa2: JSR ntoa ; Convert It
ctoa3: LDA temp1 ;Get Low Byte
JSR ntoa ;Convert It
LDA #$00
BEQ ctoax ;Terminate String
ntoa: AND #$0F ;Strip High Nybble
ORA #$30 ;Convert to ASCII digit
ctoax STA (strlo),Y ;Store in String
INY ;and Increment Offset
RTS
;Convert Binary Number in Accumulator to Binary Coded Decimal
;Uses temp0
;Returns BCD in temp1,temp and A,X = 0
cvbcd: STA temp0 ;Save Binary Value
LDA #0 ;Clear BCD Bytes
STA temp1
STA temp2
LDX #8 ;Process 8 bits of Binary
SEI ;Disable Interupts
SED ;Set Decimal Mode
cvbcdl: ASL temp0 ;Shift High Bit Into Carry
LDA temp1 ;Add BCD Low Byte to Itself
ADC temp1 ; Plus Bit Shifted out of Binary
STA temp1 ; Effectively Multiplying It by 2
LDA temp2 ;Add BCD High Byte to Itself
ADC temp2 ; Plus Bit Shifted out of Low Byte
STA temp2 ; Effectively Multiplying It by 2
DEX ;Decrement Counter and
BNE cvbcdl ; Process Next Bit
CLD ;Clear Decimal Mode
CLI ;Enable Interrupts
RTS