From b5dd6e10657cffc4f1b1631297af9308555499f2 Mon Sep 17 00:00:00 2001
From: Michael Raitza <git@spacefrogg.net>
Date: Sun, 9 Feb 2020 01:24:19 +0100
Subject: [PATCH] Start implementation as a sub class to trees

---
 cb/cb.factor | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)
 create mode 100644 cb/cb.factor

diff --git a/cb/cb.factor b/cb/cb.factor
new file mode 100644
index 0000000..3ad0957
--- /dev/null
+++ b/cb/cb.factor
@@ -0,0 +1,63 @@
+! Copyright (C) 2020 Michael Raitza
+! See http://factorcode.org/license.txt for BSD license.
+!
+! * Crit-bit trees
+! ** Rationale
+! Critbit trees are described in [[https://cr.yp.to/critbit.html][djb's crit-bit tree]]. They are an evolution of
+! PATRICIA trees showing that fast insertion, deletion, exact searching and suffix
+! searching is possible with this data structure.
+
+! The strength of this datastructure, according to its author, lies in its simple
+! design and its optimisation to be machine parsable using machine word-sized
+! operations where possible. Like PATRICIA trees, crit-bit trees are
+! prefix-compressed, with internal nodes storing next decision point (the critical
+! bit) in a length field (encoded as an integer and a mask) and two successor
+! pointers. Arbitrary data objects make up its leaves.
+
+USING: accessors kernel math sequences serialize trees trees.private ;
+IN: trees.cb;
+
+TUPLE: cb < tree ;
+
+: <cb> ( -- tree ) cb new-tree ; inline
+
+<PRIVATE
+
+TUPLE: cb-node < node byte# bits ;
+
+: <cb-node> ( byte# bits key value -- node )
+    cb-node new-node
+    >>bits
+    >>byte# ; inline
+
+! 0 = left
+! 1 = right
+: direction ( byte bits -- direction )
+    bitor 1 + -8 shift ; inline
+
+: key-side ( byte bits -- side )
+    direction 0 = -1 1 ? ;
+
+: get-byte-at ( byte# key -- byte/0 )
+    object>bytes ?nth [ 0 ] unless* ;
+
+! ** Insertion
+! Explain...
+
+DEFER: cb-set
+
+: cb-insert ( value key node -- node taller? created? )
+    2dup [ byte#>> ] [ bits>> ] bi
+    [ swap get-byte-at ] dip key-side [
+        node-link cb-set
+    ] with-side ;
+
+! Implement this and cb-insert using SYMBOL for current key bytes while
+! traversing the tree.
+: (cb-set) ( value key node -- node taller? created? )
+    ;
+
+: cb-set ( value key node -- node taller? created? )
+    [ (cb-set) ] [ swap [ [ 0 get-byte-at 0xfe ] keep ] dip <cb-node> t t ] if* ;
+
+PRIVATE>