diff options
Diffstat (limited to 'bip-0158.mediawiki')
| -rw-r--r-- | bip-0158.mediawiki | 18 |
1 files changed, 9 insertions, 9 deletions
diff --git a/bip-0158.mediawiki b/bip-0158.mediawiki index bf2e856..2062c6e 100644 --- a/bip-0158.mediawiki +++ b/bip-0158.mediawiki @@ -65,11 +65,10 @@ For each block, compact filters are derived containing sets of items associated with the block (eg. addresses sent to, outpoints spent, etc.). A set of such data objects is compressed into a probabilistic structure called a ''Golomb-coded set'' (GCS), which matches all items in the set with probability -1, and matches other items with probability <code>2^(-P)</code> for some -integer parameter <code>P</code>. We also introduce parameter <code>M</code> -which allows filter to uniquely tune the range that items are hashed onto -before compressing. Each defined filter also selects distinct parameters for P -and M. +1, and matches other items with probability <code>1/M</code> for some +integer parameter <code>M</code>. The encoding is also parameterized by +<code>P</code>, the bit length of the remainder code. Each filter defined +specifies values for <code>P</code> and <code>M</code>. At a high level, a GCS is constructed from a set of <code>N</code> items by: # hashing all items to 64-bit integers in the range <code>[0, N * M)</code> @@ -88,8 +87,8 @@ one is able to select both Parameters independently, then more optimal values can be selected<ref>https://gist.github.com/sipa/576d5f09c3b86c3b1b75598d799fc845</ref>. Set membership queries against the hash outputs will have a false positive rate -of <code>2^(-P)</code>. To avoid integer overflow, the -number of items <code>N</code> MUST be <2^32 and <code>M</code> MUST be <2^32. +of <code>M</code>. To avoid integer overflow, the number of items <code>N</code> +MUST be <2^32 and <code>M</code> MUST be <2^32. The items are first passed through the pseudorandom function ''SipHash'', which takes a 128-bit key <code>k</code> and a variable-sized byte vector and produces @@ -189,9 +188,10 @@ golomb_decode(stream, P: uint) -> uint64: ==== Set Construction ==== -A GCS is constructed from three parameters: +A GCS is constructed from four parameters: * <code>L</code>, a vector of <code>N</code> raw items -* <code>P</code>, which determines the false positive rate +* <code>P</code>, the bit parameter of the Golomb-Rice coding +* <code>M</code>, the target false positive rate * <code>k</code>, the 128-bit key used to randomize the SipHash outputs The result is a byte vector with a minimum size of <code>N * (P + 1)</code> |