implement lzss encoding

1 files changed, 36 insertions, 0 deletions

diff --git a/src/lzsschain.nim b/src/lzsschain.nim
new file mode 100644
index 0000000..8203cb8
--- /dev/null
+++ b/src/lzsschain.nim
@@ -0,0 +1,36 @@
+# 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, tables, sugar
+import polyfill, integers, lzssnode
+
+const maxChainByteLength = 32_000 * wordBitLength
+
+type LzssChain* =
+  SinglyLinkedList[LzssNode]
+
+proc lzssChain*(): LzssChain =
+  initSinglyLinkedList[LzssNode]()
+
+proc decode*(lzssChain: LzssChain): seq[uint8] =
+  result = newSeqOfCap[uint8](maxChainByteLength)
+  for node in lzssChain.items:
+    case node.kind:
+      of character:
+        result.add(node.character)
+      of reference:
+        let absolutePos = result.len - node.relativePos
+        result.add(result.toOpenArray(absolutePos, absolutePos + node.length - 1))