Standards (was [BitTorrent] Back to Merkle Hash Trees...)

Martin Nilsson yahoo at
Wed Feb 9 00:21:57 EST 2005

Justin Cormack wrote:
> Doing the maths, a 4G file with 64k pieces/chunks will have 64k of them,
> which means a bitmap is 8k, which is smaller than a request (64k) so
> thats not a huge transfer. you will get 64k have messages (worst case)
> which is 512k. These figures are per peer.

Many times (seeds and recently started peers) it is also possible to 
apply high compression to the bitmap. Recursively divide the bitmap into 
two parts and make a binary tree. Then encode the the tree from the top with

00 - subtree all zeroes
01 - two nodes follows
10 - unencoded subtree follows
11 - subtree all ones

/Martin Nilsson

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