better way to generate a permutation?

I'm putting the polish on pnmstega/pnmdestega. Currently they spend the largest part of their time generating the permuted list of bit positions to use for storing the data bits. Not surprising, I knew the first version would be slow - it actually mallocs an array, fills it with numbers, and shuffles them. Now I'm looking for suggestions on better methods. I looked in Knuth, Sedgewick, and Schneier, and didn't find anything. Send email if you've got an idea. Something with a bit vector might work. --- Jef