Bitwise IO: Difference between revisions
Content added Content deleted
Puppydrum64 (talk | contribs) No edit summary |
Puppydrum64 (talk | contribs) |
||
Line 23:
<br><br>
=={{header|6502 Assembly}}==
===Storing Bytes As ASCII Strings===
This routine converts a byte to a sequence of ASCII zeroes and ones, and stores them in a null-terminated string. Works in Easy6502.
Multiple bytes can be stored this way simply by loading a new value in the accumulator and calling the subroutine again. Since Y is still pointed at the null terminator, no re-adjustment of <code>z_BC</code> or Y is necessary.
<lang 6502asm>define StringRam $1200 ;not actually used in the code, but it's here for clarity.
define z_BC $00 ;fake Z80-style register for pseudo-16-bit operations.
Line 69 ⟶ 71:
1200: 30 30 30 30 31 31 31 31 00
</pre>
===Compressing a String of ASCII Zeroes and Ones===
Building on the above, the process can be reversed. The output of the first function becomes the input of the second. Some of the above is repeated, this is to show the two working in sequence.
<lang 6502asm>define StringRam $1200
define BitRam $1400
define z_BC $00
define z_C $00
define z_B $01
define z_DE $02
define z_E $02
define z_D $03
define tempMath $04
define tempBitMask $05
define tempY $06
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
LDA #0
TAX
TAY ;clear data regs (not needed on Easy6502 but it's a good practice at the start of a program on real hardware)
loop_clearRam:
STA $1200,x
STA $1400,x
inx
bne loop_clearRam
lda #$12
sta z_B
lda #$00
sta z_C
lda #$0F
jsr Hex2BinAscii ;store first string
lda #$FF
jsr Hex2BinAscii ; store second string
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
LDA #$12
STA z_B
LDA #$00
STA z_C ; get address of string Ram (this step isn't necessary as they're already loaded but it's here for clarity)
LDA #$14
STA z_D
LDA #$00
STA z_E ; get address of destination
LDY #$00
STY tempY ; the indices into StringRam and BitRam are different.
jsr CompressBits
brk
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
Hex2BinAscii:
; this procedure is the same as the above example.
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
CompressBits:
; takes a stream of ascii zeroes and ones,
; and packs them into a series of bytes.
LDX #8 ; repeat 8 times.
LDA #0
STA tempMath ;zero out tempMath
;;;;;;;;;;;;;;;;;;;;;;;;;
loop_CompressBits:
LDA (z_BC),y
beq Terminated ; if the value read the null terminator, we are done.
AND #$0F ; returns either 0 or 1 in bit 0. There is no error checking for invalid input at the moment.
ror ; accumulator is rotated into the carry flag.
rol tempMath ; the carry is shifted into the bottom of tempMath.
; repeating this with each successive ascii bit representation
; will preserve the order of the bits. It's hard to explain without drawing a picture
; but trust me it just works.
iny ; next Y
dex
bne loop_CompressBits
;;;;;;;;;;;;;;;;;;;;;;;;;
; loop overhead
tya
pha ; backup source index.
ldy tempY
lda tempMath
sta (z_DE),y
inc tempY ; increment destination index
pla
tay ; restore source index
jmp CompressBits ; back to top
;;;;;;;;;;;;;;;;;;;;;;;;;
Terminated:
rts</lang>
{{out}}
<pre>
1400: 0f ff
</pre>
=={{header|Ada}}==
| |||