fix: construct BigInt with lower bit first

src/main/scala/uvm/refimpl/itpr/IRBuilderCommInstExecutor.scala

@@ -24,8 +24,10 @@ object IRBuilderCommInstExecutor {
 
   def unsignedLongSeqToBigInt(nums: Seq[Long]): BigInt = {
     var bigNum = BigInt(0)
+    var i = 0
     for (num <- nums) {
-      bigNum = (bigNum << 64) | (BigInt(num) & 0xffffffffffffffffL)
+      bigNum = bigNum | ((BigInt(num) & 0xffffffffffffffffL) << 64 * i)
+      i += 1
     }
     bigNum
   }

src/main/scala/uvm/refimpl/nat/NativeMemoryAccessHelper.scala

@@ -22,13 +22,15 @@ object NativeMemoryAccessHelper {
     val str = theMemory.getString(base, len.toInt, StandardCharsets.US_ASCII)
     str
   }
-  
+
   def unsignedLongSeqToBigInt(nums: Seq[Long]): BigInt = {
-      var bigNum = BigInt(0)
-      for (num <- nums) {
-        bigNum = (bigNum << 64) | (BigInt(num) & 0xffffffffffffffffL)
-      }
-      bigNum
+    var bigNum = BigInt(0)
+    var i = 0
+    for (num <- nums) {
+      bigNum = bigNum | ((BigInt(num) & 0xffffffffffffffffL) << 64 * i)
+      i += 1
+    }
+    bigNum
   }
 
   def readIntArray(base: Long, len: Long): IndexedSeq[Int] = {