Base-52 for DMM conversion

ID:142546
 
Apr 27 2008, 9:11 am (Edited on Apr 27 2008, 9:17 am)
Code:
mob/verb/test_symbol_index(index as num)
    var/symbols_length = (index == 1 ? 1 : round(log(52,index-1)) + 1)
    . = ""
    for(var/i = symbols_length-1, i >= 0, i--)
        var/base_symbol = round((index-1) / (52**i))
        usr << base_symbol
        if(base_symbol < 26)
            if(base_symbol == -1) . += "Z" //bugfix hack
            else . += ascii2text(base_symbol+97)
        else . += ascii2text(base_symbol+39)
        index %= 52**i
    usr << .


Problem description:
DMM files store map symbols in base-52, "numbered" from [a-zA-Z].

If you'll note the comment above, I had to apply a hack to the system because for the even multiples of 52**n (except 52!), the system produces a -1 result for every symbol after the first.

Could anyone help me fix this so I don't need the hack? I'm not sure I understand why it's coming up in the first place.


The procedure is intended to take an integer greater than zero and convert it into the DMM-format base-52.
Apr 27 2008, 11:57 am (Edited on Apr 27 2008, 7:10 pm)
I have this in pif_MapLoader's source. Here's the code I use. Unfortunately, it has a nested loop, but it's never shown significant slowdown for me.
#define num2letter(x) ascii2text((x) + 96 - ((x) > 26 && 58))

proc/combinations(x)
    var/list/combinations[0]

    var/amount = round(log(52, x)) + 1
    if(52 ** (amount) == x) amount ++

    var/list/num[amount]
    for(var/a = 1 to num.len) num[a] = 1

    for(var/a = 1 to x)
        var/string
        for(var/e in num) string = "[num2letter(e)][string]"
        combinations += string

        count_list(num)

    for(var/a = 1 to combinations.len) condition[condition[a]] = combinations[a]