Re: [SLUG] Numeric Storage Format

From: Ian C. Blenke (icblenke@nks.net)
Date: Fri Dec 29 2006 - 02:27:07 EST

Eben King wrote:
>> nstr = "57";
>> ch = nstr[0] - '0';
>> number = 10 * ch + nstr[1] - '0';
>
> So in memory it'd be '5' '7' NUL = 0x35 0x37 0x00, right?

The source ASCII string, nstr, is "57", which would be 0x35 0x37 0x00 as
a null terminated string, correct.

>> Okay, now after all the explanation, what is this storage format
>> *called*? It's not BCD, and it's not packed decimal. I'd like to know
>> what it's called, so I can look up references on it.
>
> I'd call it "stored as an ASCII string" m'self, but ICBW.

I think he is saying that he is converting from an ASCII string to this
format. The format is a binary representation of the number, by
subtracting the value of an ASCII "0", ie:

    0x35 0x37 0x00

becomes

    0x05 0x07
or
    number=10 * 0x05 + 0x07
so that
    number=57

ie, an integer representation of the string.

The question boils down to how to handle negative numbers: one's
complement or two's complement. I'll wager that it is the latter.

- Ian


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