On Wed, May 6, 2009 at 11:42 PM, Todd B. removed_email_address@domain.invalid

wrote:

something. According to what I’ve read so far, base64 is not, and

base62 is, except for that paper written in a scientific journal that

I don’t have access to (but, for the summary, of course). I suppose

that is what the OP wanted anyway.

No, it’s a number base transformation. Here’s an example using base 7

(as being easier to work with than 62 :)):

letting n = 1250, and using # as a divmod operator:

1250 # 7 = 178, 4

178 # 7 = 25, 3

25 # 7 = 3, 4

3 # 7 = 0, 3 <-- we have reached n=0, so the loop terminates

so 1250[base 10] = 3434 [base 7]

If you think about it, base 10 works the same way:

1250 # 10 = 125, 0

125 # 10 = 12, 5

12 # 10 = 1, 2

1 # 10 = 0, 1

so 1250[base 10] = 1250[base 10]

To go the other way, you repeatedly add the least significant digit

and multiply by the base

so 3434[7]

start with 0, and read the digits in forward order

(0 * 7) + 3 = 3

3 * 7 + 4 = 25

24 * 7 + 3 = 178

178 * 7 + 4 = 1250 <— et voila!

martin

martin