refs #35 minimal serialization of simple types in bit-effective format

lynglib/src/commonMain/kotlin/net/sergeych/lynon/LynonDecoder.kt

@@ -0,0 +1,45 @@
+package net.sergeych.lynon
+
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.obj.Obj
+import net.sergeych.lyng.obj.ObjClass
+
+open class LynonDecoder(private val bin: BitInput) {
+
+    val cache = mutableListOf<Obj>()
+
+    fun unpackObject(scope: Scope, type: ObjClass): Obj {
+        return if( bin.getBit() == 0 ) {
+            // unpack and cache
+            val cached = bin.getBool()
+            type.deserialize(scope, this).also {
+                if( cached ) cache.add(it)
+            }
+        }
+        else {
+            // get cache reference
+            val size = sizeInBits(cache.size)
+            val id = bin.getBitsOrNull(size)?.toInt() ?: scope.raiseError("Invalid object id: unexpected end of stream")
+            if( id >= cache.size ) scope.raiseError("Invalid object id: $id should be in 0..<${cache.size}")
+            cache[id]
+        }
+    }
+
+    fun unpackBinaryData(): ByteArray? {
+        val size = bin.unpackUnsigned()
+        return bin.getBytes(size.toInt())
+    }
+
+    fun unpackBoolean(): Boolean {
+        return bin.getBit() == 1
+    }
+
+    fun unpackDouble(): Double {
+        return Double.fromBits(bin.getBits(64).toLong())
+    }
+
+    fun unpackSigned(): Long {
+        return bin.unpackSigned()
+    }
+
+}