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This is an archived, read-only copy of the United-TI subforum , including posts and topic from May 2003 to April 2012. If you would like to discuss any of the topics in this forum, you can visit Cemetech's z80 Assembly subforum. Some of these topics may also be directly-linked to active Cemetech topics. If you are a Cemetech member with a linked United-TI account, you can link United-TI topics here with your current Cemetech topics.

This forum is locked: you cannot post, reply to, or edit topics. Z80 & 68k Assembly => z80 Assembly
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United-TI Archives -> Z80 & 68k Assembly
 
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AHBAD_ALVIN


Advanced Newbie


Joined: 18 Sep 2010
Posts: 74
Posted: 06 Oct 2010 05:22:21 pm    Post subject:
Hello, I have a quick question...

For my parser, I want to change decimal numbers written in ASCII code to pure hex code. I know this is possible, as Axe and the OS do this quite frequently. How exactly do I do this quickly and memory efficiently?
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calc84maniac


Elite


Joined: 22 Jan 2007
Posts: 770
Posted: 06 Oct 2010 08:24:00 pm    Post subject:
Here is a z80 routine I whipped up, which will read ASCII digits pointed to by DE into a binary number in HL, stopping when a non-digit character is reached.

Code:

;Start with 0
  ld hl,0
digitLoop:
;Read character and make sure it is a digit
  ld a,(de)
  sub '0'
  cp 10
  jr nc,notADigit
;Increment pointer
  inc de
;Multiply HL by 10
  ld b,h
  ld c,l
  add hl,hl
  add hl,hl
  add hl,bc
  add hl,hl
;Add the digit value in A to HL
  add a,l
  ld l,a
  jr nc,digitLoop
  inc h
  jr digitLoop
notADigit:

Edit: Made it actually stop where the non-digit was found instead of the character afterward.

Last edited by Guest on 06 Oct 2010 08:25:12 pm; edited 1 time in total
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AHBAD_ALVIN


Advanced Newbie


Joined: 18 Sep 2010
Posts: 74
Posted: 07 Oct 2010 04:21:12 am    Post subject:
calc84maniac wrote:

Here is a z80 routine I whipped up, which will read ASCII digits pointed to by DE into a binary number in HL, stopping when a non-digit character is reached.

Code:

;Start with 0
  ld hl,0
digitLoop:
;Read character and make sure it is a digit
  ld a,(de)
  sub '0'
  cp 10
  jr nc,notADigit
;Increment pointer
  inc de
;Multiply HL by 10
  ld b,h
  ld c,l
  add hl,hl
  add hl,hl
  add hl,bc
  add hl,hl
;Add the digit value in A to HL
  add a,l
  ld l,a
  jr nc,digitLoop
  inc h
  jr digitLoop
notADigit:

Edit: Made it actually stop where the non-digit was found instead of the character afterward.

Thanks for your help! Smile
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AHBAD_ALVIN


Advanced Newbie


Joined: 18 Sep 2010
Posts: 74
Posted: 07 Oct 2010 12:41:44 pm    Post subject:
Oh, and I just improved it some while fooling around with Mimas during my history class. But of course, this is only a minor addition so that it only reads five digits of a number (next addition will to make it only accept numbers less than 65353).


Code:

;Start with 0
  db DD
  ld l,5
  ld hl,0
digitLoop:
;push the a register and then compare to IXL
  dec ix
  push af 
  ld a,0
  db DD
  cp l
  jr z,notADigit 
  pop af
;Read character and make sure it is a digit
  ld a,(de)
  sub '0'
  cp 10
  jr nc,notADigit
;Increment pointer
  inc de
;Multiply HL by 10
  ld b,h
  ld c,l
  add hl,hl
  add hl,hl
  add hl,bc
  add hl,hl
;Add the digit value in A to HL
  add a,l
  ld l,a
  jr nc,digitLoop
  inc h
  jr digitLoop
notADigit:
  ret
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