Add Pigeon::Helpers.lipmaa in preparation for lipmaa backlinking

README.md

@@ -53,11 +53,11 @@ Eg: `pigeon identity show` becomes `./pigeon-cli show`.
  - [X] Message.ingest should be the only code path to message authoring.
  - [X] Don't allow any type of whitespace in `kind` or `string` keys. Write a test for this.
  - [X] Run Flog / Flay and friends to find duplications. Will aid in port to other languages.
- - [ ] Make all methods private except those required for the CLI.
- - [ ] Make CLI names consistent with API names. Eg: find vs. read.
+ - [X] Make all methods private except those required for the CLI.
  - [ ] Add Lipmaa links like the Bamboo folks do.
- - [ ] Create regexes in ::Lexer using strings and Regexp.new() for cleaner regexes.
  - [ ] Make the switch to LevelDB, RocksDB, [UNQLite](https://unqlite.org/features.html) or similar (currently using Ruby PStore).
+ - [ ] Make CLI names consistent with API names. Eg: find vs. read.
+ - [ ] Create regexes in ::Lexer using strings and Regexp.new() for cleaner regexes.
  - [ ] Need a way of importing / exporting a feeds blobs. (see "Bundle Brainstorming" below)
  - [ ] Need a way of adding peers messages / gossip to bundles. (see "Bundle Brainstorming" below)
  - [ ] Add mandatory `--since=` arg to `bundle create`

dist/pigeon.rb

@@ -83,6 +83,28 @@ module Pigeon
       "X" => 0b11101, "Y" => 0b11110, "Z" => 0b11111,
     }.freeze
 
+    def self.lipmaa(n)
+      m, po3, x = 1, 3, n
+      # find k such that (3^k - 1)/2 >= n
+      while (m < n)
+        po3 *= 3
+        m = (po3 - 1) / 2
+      end
+      po3 /= 3
+      # find longest possible backjump
+      if (m != n)
+        while x != 0
+          m = (po3 - 1) / 2
+          po3 /= 3
+          x %= m
+        end
+        if (m != po3)
+          po3 = m
+        end
+      end
+      return n - po3
+    end
+
     # http://www.crockford.com/wrmg/base32.html
     def self.b32_encode(string)
       string