Re: Please help me make the .template files for Debian CDs smaller
On Fri, Mar 21, 2003 at 07:19:04PM -0700, Chris Tillman wrote:
> Another idea, would be to special case the jigdo code to check the file
> size first, and do something special if it's 1474560 or 2941920 bytes, or
> the other standard floppy sizes.
Well, there's no "something special" that can be done: jigdo-file
gets as input a finished CD/DVD image. At some unknown offset inside this
big file is a copy of the floppy image.
jigdo-file first creates a checksum of the first 1k of all files it wants
to find, then moves a 1k-sized "window" over the image, comparing the image
checksum of that window to the files' checksums.
Once the checksum of the start of a file matches, the subsequent data is
also compared. Such "possible future file matches" are held in a queue
whose size *must* be fixed because jigdo-file would get prohibitively slow
(O(imagesize^2) worst-case) if it were allowed to grow indefinitely.
There are a number of things I can fine-tune, though, such as the window
size and a certain heuristics inside jigdo-file. But the problem remains
very difficult, I'm not sure whether I'll be successful... for example,
increasing the window size to 4k would prevent it from finding all .debs
which are smaller than 4k.
|_) /| Richard Atterer | CS student at the Technische | GnuPG key:
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