add huffman decoder

3 files changed, 80 insertions, 3 deletions

diff --git a/src/huffmandecoder.nim b/src/huffmandecoder.nim
new file mode 100644
index 0000000..4df712a
--- /dev/null
+++ b/src/huffmandecoder.nim
@@ -0,0 +1,34 @@
+# gzip-like LZSS compressor
+# Copyright (C) 2018  Pacien TRAN-GIRARD
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+import huffmantree, bitreader
+
+type HuffmanDecoder*[T: SomeUnsignedInt] = object
+  tree: HuffmanTreeNode[T]
+
+proc decoder*[T](tree: HuffmanTreeNode[T]): HuffmanDecoder[T] =
+  HuffmanDecoder[T](tree: tree)
+
+proc decode*[T](decoder: HuffmanDecoder[T], bitReader: BitReader): T =
+  proc walk(node: HuffmanTreeNode[T]): T =
+    case node.kind:
+      of branch:
+        case bitReader.readBool():
+          of false: walk(node.left)
+          of true: walk(node.right)
+      of leaf:
+        node.value
+  walk(decoder.tree)
diff --git a/src/huffmantree.nim b/src/huffmantree.nim
index c57b55c..44c9990 100644
--- a/src/huffmantree.nim
+++ b/src/huffmantree.nim
@@ -24,12 +24,12 @@ type HuffmanTreeNodeKind* = enum
   leaf
 
 type HuffmanTreeNode*[T: SomeUnsignedInt] = ref object
-  case kind: HuffmanTreeNodeKind
+  case kind*: HuffmanTreeNodeKind
     of branch:
-      left, right: HuffmanTreeNode[T]
+      left*, right*: HuffmanTreeNode[T]
       maxChildValue: T
     of leaf:
-      value: T
+      value*: T
   weight: int
 
 proc huffmanBranch*[T](left, right: HuffmanTreeNode[T]): HuffmanTreeNode[T] =
diff --git a/tests/thuffmandecoder.nim b/tests/thuffmandecoder.nim
new file mode 100644
index 0000000..d4d81b4
--- /dev/null
+++ b/tests/thuffmandecoder.nim
@@ -0,0 +1,43 @@
+# gzip-like LZSS compressor
+# Copyright (C) 2018  Pacien TRAN-GIRARD
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+import unittest, streams
+import bitreader, bitwriter
+import huffmantree, huffmandecoder
+
+suite "huffdecoder":
+  let tree = huffmanBranch(
+    huffmanLeaf(1'u),
+    huffmanBranch(
+      huffmanLeaf(2'u),
+      huffmanLeaf(3'u)))
+
+  test "decode":
+    let stream = newStringStream()
+    defer: stream.close()
+    let bitWriter = stream.bitWriter()
+    bitWriter.writeBool(true)  # 2
+    bitWriter.writeBool(false)
+    bitWriter.writeBool(false) # 1
+    bitWriter.writeBool(true)  # 3
+    bitWriter.writeBool(true)
+    bitWriter.flush()
+    stream.setPosition(0)
+    let bitReader = stream.bitReader()
+    let decoder = tree.decoder()
+    check decoder.decode(bitReader) == 2'u
+    check decoder.decode(bitReader) == 1'u
+    check decoder.decode(bitReader) == 3'u