Add a custom codec test for com.epam.deltix.dfp.Decimal64 values through scala.BigDecimal as a possible workaround for #1046

Author: plokhotnyuk

build.sbt

@@ -176,6 +176,7 @@ lazy val `jsoniter-scala-macros` = crossProject(JVMPlatform, JSPlatform, NativeP
       )
       case _ => Seq()
     }) ++ Seq(
+      "com.epam.deltix" % "dfp" % "1.0.1" % Test,
       "org.scalatest" %%% "scalatest" % "3.2.17" % Test,
       "org.scala-lang.modules" %%% "scala-collection-compat" % "2.11.0" % Test
     )

jsoniter-scala-macros/jvm/src/test/scala/com/github/plokhotnyuk/jsoniter_scala/macros/JsonCodecMakerDecimal64Spec.scala

@@ -0,0 +1,46 @@
+package com.github.plokhotnyuk.jsoniter_scala.macros
+
+import com.epam.deltix.dfp.{Decimal64, Decimal64Utils}
+import com.github.plokhotnyuk.jsoniter_scala.core._
+import com.github.plokhotnyuk.jsoniter_scala.macros.JsonCodecMaker._
+
+class JsonCodecMakerDecimal64Spec extends VerifyingSpec {
+  import Decimal64Codec._
+
+  "Decimal64Codec" should {
+    "deserialize both numeric and string representation of numbers to canonized Decimal64 values" in {
+      verifyDeser(make[List[Decimal64]],
+        List(Decimal64.ONE_TENTH, Decimal64.MILLION, Decimal64.fromLong(4503599627370497L), Decimal64.parse("1.23456789e+309"), Decimal64.MAX_VALUE),
+        """[0.1,"001000000",4503599627370497,1.23456789e+309,"9999999999999999e+369"]""")
+    }
+    "serialize Decimal64 values into numeric or string representation depending on number of mantissa bits of canonized in-memory representation" in {
+      verifySer(make[List[Decimal64]],
+        List(Decimal64.ONE_TENTH, Decimal64.MILLION, Decimal64.fromLong(4503599627370497L), Decimal64.parse("1.23456789e+309"), Decimal64.MAX_VALUE),
+        """[0.1,1E+6,"4503599627370497","1.23456789E+309","9.999999999999999E+384"]""")
+    }
+  }
+}
+
+object Decimal64Codec {
+  implicit val codec: JsonValueCodec[Decimal64] = new JsonValueCodec[Decimal64] {
+    override def decodeValue(in: JsonReader, default: Decimal64): Decimal64 =
+      Decimal64.fromUnderlying(Decimal64Utils.canonize(Decimal64Utils.fromBigDecimal((if (in.isNextToken('"')) {
+        in.rollbackToken()
+        in.readStringAsBigDecimal(null)
+      } else {
+        in.rollbackToken()
+        in.readBigDecimal(null)
+      }).bigDecimal)))
+
+    override def encodeValue(x: Decimal64, out: JsonWriter): Unit = {
+      val cx = Decimal64Utils.canonize(Decimal64.toUnderlying(x))
+      val bd = new BigDecimal(Decimal64Utils.toBigDecimal(cx))
+      val m = Decimal64Utils.getUnscaledValue(cx)
+      val s = Decimal64Utils.getScale(cx)
+      if (m >= -4503599627370496L && m <= 4503599627370496L && s >= -256 && s <= 256) out.writeVal(bd)
+      else out.writeValAsString(bd)
+    }
+
+    override def nullValue: Decimal64 = null
+  }
+}