How to convert ascii number to binary in MC68k

Question

I have to write a program that requires 20 user inputted numbers from 0-100 to find the average of the numbers and categorize them as failing or passing but it saves the input as ascii in memory and I have to change it from ascii to binary. I know that ascii numbers are 30-39 in hex but I am unsure about how to implement it in MC68K like if i input 93 as a number then it would be saved as 3933 but how do I convert it to binary?

Subtract '0'? (Which, as you already know, is `0x30` in hex.) — Jongware, Apr 06 '14 at 21:33
doesnt work because 3933 in hex is way larger than 93. So I have to convert it so that it gives the value 93. — user1869703, Apr 06 '14 at 21:45
But every single *digit* is entered in ASCII. So you have to subtract 0x30 from every digit as well. (You'll end up with a series of 'pure' binary digits, which you then need to combine into a single binary number. Basic arithmetic, I'm afraid.) — Jongware, Apr 06 '14 at 21:47
Yes, I know that 3933 split up as 39 33 can each be subtracted by 30 to get 93 but that isn't what i'm asking for. Say I input 93 and that is saved as 3933 but I want it to give me the hex value of "5D" — user1869703, Apr 06 '14 at 22:02
Um, you lost me there. If you have a list of correct (binary) values, you can combine them in the *usual* way to get a total of '93' (which is your '5D'). — Jongware, Apr 06 '14 at 22:05
So in easy68k it'll save as a 3933 but it is all in hex. if i only subtract then itll give me 93 in hex which is 147 in decimal. — user1869703, Apr 06 '14 at 22:08
Losing you even more. I'm going to log off until you clarify your question. Are you confusing "binary" with "hex"? Your last statement suggests you need to, or *think* you need to, enter and/or convert from *hex* input. — Jongware, Apr 06 '14 at 23:55
In easy68k The values are stored as Hex. So if I have 3933 and I only subtract 30 then it will remain as a hex. So I will have to do a subroutine that will do more than just subtract because I need it as exactly "5D". It will not convert the "93" by just subtracting because sure i can subtract 0x30 but itll only leave me with more hex values. — user1869703, Apr 07 '14 at 07:07
As has already been mentioned, you need to subtract `0x30` from each byte, then you combine these by multiplying each byte with increasing powers of 10 and adding the results. — Michael, Apr 07 '14 at 08:00
Oh. I realized i was multiplying the first one by ten as well. thats why it wasnt working. — user1869703, Apr 08 '14 at 01:30
Not sure if i can help, but first seperate a half byte (Nibble) and if the value is greater then ASCII "9", then simple add the value of 7 for to convert to an ASCII of A - F, if you want hexadecimal output. — Dirk Wolfgang Glomp, Apr 08 '14 at 19:44

turboscrew · Answer 1 · 2014-04-07T21:54:08.387

0

  clear number
loop:
  get highest digit character not dealt with yet
  compare digit character to '0' ; that's character 0, not value 0
  blo done
  compare digit character to '9'
  bhi done
  multiply number by 0x0a ; 10 in decimal
  subtract 0x30 from the character
  add to number
  jmp loop
cone:
  ...

edited Apr 07 '14 at 21:54

answered Apr 07 '14 at 21:48

turboscrew

676
4
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score 0 · Answer 2 · answered Apr 09 '14 at 11:09

Here's how I would do it:

str_to_int:
    ; Converts a decimal signed 0-terminated string in a0 into an integer in d0.
    ; Stops on the first non-decimal character. Does not handle overflow.
    ; Trashes other registers with glee.
    moveq #0, d3
.signed:
    cmpi.b #'-',(a0)     ; Check for leading '-'.
    bne.s  .convert
    bchg   #0,d3
    addq.l #1,a0
    bra.s  .signed
.convert:
    moveq.l #0,d0
    moveq.l #0,d1
.digit:
    move.v (a0)+,d1
    beq.s  .done
    subi.b #'0',d1       ; Convert to integer.
    bmi.s  .done         ; If < 0, digit wasn't valid.
    cmpi.b #'9'-'0',d1
    bgt.s  .done         ; If larger than 9, done.
    muls.l #10,d0
    add.l  d1,d0
    bra.s  .digit
.done:
    tst.b  d3
    bne.s  .signed
    rts
.signed:
    neg.l  d0
    rts

Note: the above is untested assembly code for a processor I haven't touched in ... quite a while. Hopefully it can at least be inspirational. Back in the day, of course nobody would have dared use muls here, but it's instructional. Pardon the pun.

How to convert ascii number to binary in MC68k

2 Answers2