implement lzss block

4 files changed, 134 insertions, 0 deletions

diff --git a/src/lzsshuffman/lzsshuffmandecoder.nim b/src/lzsshuffman/lzsshuffmandecoder.nim
new file mode 100644
index 0000000..cd71914
--- /dev/null
+++ b/src/lzsshuffman/lzsshuffmandecoder.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 lists
+import ../bitio/bitreader
+import ../lzss/listpolyfill, ../lzss/lzssnode, ../lzss/lzsschain
+import ../huffman/huffmantree, ../huffman/huffmandecoder
+import lzsshuffmansymbol
+
+proc readChain*(bitReader: BitReader, symbolDecoder, positionDecoder: HuffmanDecoder[uint16], maxDataByteLength: int): LzssChain =
+  var chain = lzssChain()
+  var (symbol, byteCursor) = (symbolDecoder.decode(bitReader).Symbol, 0)
+  while not symbol.isEndMarker():
+    if byteCursor > maxDataByteLength: raise newException(IOError, "lzss block too long")
+    if symbol.isCharacter():
+      chain.append(lzssCharacter(symbol.uint8))
+    else:
+      let position = positionDecoder.decode(bitReader)
+      chain.append(unpackLzssReference(symbol, position))
+    (symbol, byteCursor) = (symbolDecoder.decode(bitReader).Symbol, byteCursor + 1)
+  chain
diff --git a/src/lzsshuffman/lzsshuffmanencoder.nim b/src/lzsshuffman/lzsshuffmanencoder.nim
new file mode 100644
index 0000000..ea89f85
--- /dev/null
+++ b/src/lzsshuffman/lzsshuffmanencoder.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 lists
+import ../bitio/bitwriter
+import ../lzss/listpolyfill, ../lzss/lzssnode, ../lzss/lzsschain, ../lzss/lzssencoder
+import ../huffman/huffmantree, ../huffman/huffmantreebuilder, ../huffman/huffmanencoder
+import lzsshuffmansymbol
+
+proc writeSymbol(bitWriter: BitWriter, encodedSymbol: tuple[bitLength: int, value: uint16]) =
+  bitWriter.writeBits(encodedSymbol.bitLength, encodedSymbol.value)
+
+proc writeChain*(lzssChain: LzssChain, symbolEncoder, positionEncoder: HuffmanEncoder[uint16, uint16], bitWriter: BitWriter) =
+  for node in lzssChain.items:
+    case node.kind:
+      of character:
+        bitWriter.writeSymbol(symbolEncoder.encode(node.character))
+      of reference:
+        bitWriter.writeSymbol(symbolEncoder.encode(shiftLzssLength(node.length)))
+        bitWriter.writeSymbol(positionEncoder.encode(node.relativePos.uint16))
+  bitWriter.writeSymbol(symbolEncoder.encode(endSymbol))
diff --git a/src/lzsshuffman/lzsshuffmanstats.nim b/src/lzsshuffman/lzsshuffmanstats.nim
new file mode 100644
index 0000000..037ce5f
--- /dev/null
+++ b/src/lzsshuffman/lzsshuffmanstats.nim
@@ -0,0 +1,32 @@
+# 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 tables, lists
+import ../lzss/lzssnode, ../lzss/lzsschain
+import lzsshuffmansymbol
+
+proc aggregateStats*(chain: LzssChain): tuple[symbolTable, positionTable: CountTableRef[uint16]] =
+  var (symbolTable, positionTable) = (newCountTable[uint16](), newCountTable[uint16]())
+  for node in chain.items:
+    case node.kind:
+      of character:
+        symbolTable.inc(node.character)
+      of reference:
+        symbolTable.inc(shiftLzssLength(node.length))
+        positionTable.inc(node.relativePos.uint16)
+  symbolTable.inc(endSymbol)
+  if positionTable.len < 1: positionTable.inc(0) # ensure non-empty tree
+  (symbolTable, positionTable)
diff --git a/src/lzsshuffman/lzsshuffmansymbol.nim b/src/lzsshuffman/lzsshuffmansymbol.nim
new file mode 100644
index 0000000..cfd3fe4
--- /dev/null
+++ b/src/lzsshuffman/lzsshuffmansymbol.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 lists
+import ../lzss/lzssnode, ../lzss/lzssencoder
+
+type Symbol* = uint16
+
+const endSymbol* = 256.Symbol
+
+proc isEndMarker*(symbol: Symbol): bool =
+  symbol == endSymbol
+
+proc isCharacter*(symbol: Symbol): bool =
+  symbol < endSymbol
+
+proc unpackLzssReference*(symbol: Symbol, position: uint16): LzssNode =
+  lzssReference(symbol.int - endSymbol.int - 1 + matchGroupLength, position.int)  
+
+proc shiftLzssLength*(length: int): uint16 =
+  (length + endSymbol.int + 1 - matchGroupLength).uint16