算法错误

Question

I have a script:

function convert($src, $srcAlphabet = '0123456789', $dstAlphabet =
    'qwertyuiopasdfghjklzxcvbnm')
{
    $srcBase = strlen($srcAlphabet);
    $dstBase = strlen($dstAlphabet);

    $wet = $src;
    $val = 0;
    $mlt = 1;

    while($l = strlen($wet))
    {
        $digit = $wet[$l - 1];
        $val += $mlt * strpos($srcAlphabet, $digit);
        $wet = substr($wet, 0, $l - 1);
        $mlt *= $srcBase;
    }

    $wet = $val;
    $dst = '';

    while($wet >= $dstBase)
    {
        $digitVal = $wet % $dstBase;
        $digit = $dstAlphabet[$digitVal];
        $dst = $digit . $dst;
        $wet /= $dstBase;
    }

    $digit = $dstAlphabet[$wet];
    $dst = $digit . $dst;

    return $dst;
}

for($i = 0; $i < 10000; $i++)
{
    echo $i . ' = ' . convert(substr(' ' . $i, 1)) . '<br>';
}

It works fine, however the result is strange... it looks like that:

0 = q
1 = w
2 = e
3 = r
4 = t
5 = y
6 = u
7 = i
8 = o
9 = p
10 = a
11 = s
12 = d
13 = f
14 = g
15 = h
16 = j
17 = k
18 = l
19 = z
20 = x
21 = c
22 = v
23 = b
24 = n
25 = m
26 = wq
...
...
676 = wqq
677 = wqw
678 = wqe
...

but 26 should be qq, 676 should be qqq, 677 = qwq, 678 = qqe etc.

why it's starting from w instead of q (except for 0)?

Answer 1

If you change

$wet /= $dstBase;

to

$wet = $wet / $dstBase - 1;

your code will give the correct result. However, as Soren noted, using PHP functionality you can accomplish things much easier.