More efficient reading of BigInt and BigDecimal values with 37+ digit mantissa

Author: plokhotnyuk

jsoniter-scala-core/js/src/main/scala/com/github/plokhotnyuk/jsoniter_scala/core/JsonReader.scala

@@ -2802,11 +2802,13 @@ final class JsonReader private[jsoniter_scala](
       pos += 9
       first = Math.max(first - 1, 0)
       var i = last
-      while (i >= first) {
+      while ({
         x += (magnitude(i) & 0xFFFFFFFFL) * 1000000000
         magnitude(i) = x.toInt
-        x >>>= 32
         i -= 1
+        i >= first
+      }) {
+        x >>>= 32
       }
     }
     val bs = new Array[Byte](last + 1 << 2)

jsoniter-scala-core/jvm/src/main/scala/com/github/plokhotnyuk/jsoniter_scala/core/JsonReader.scala

@@ -2847,13 +2847,18 @@ final class JsonReader private[jsoniter_scala](
       first = Math.max(first - 8, 0)
       var i = last
       val q = 1000000000000000000L
-      while (i >= first) {
-        val m = ByteArrayAccess.getLong(magnitude, i)
-        val p = m * q
-        x += p
+      var m, mq = 0L
+      while ({
+        m = ByteArrayAccess.getLong(magnitude, i)
+        mq = m * q
+        x += mq
         ByteArrayAccess.setLong(magnitude, i, x)
-        x = Math.multiplyHigh(m, q) + (m >> 63 & q) + ((~x & p) >>> 63) // FIXME: Use Math.unsignedMultiplyHigh after dropping of JDK 17 support
         i -= 8
+        i >= first
+      }) {
+        x = (~x & mq) >>> 63
+        x += Math.multiplyHigh(m, q)
+        x += m >> 63 & q
       }
     }
     var i = 0

jsoniter-scala-core/native/src/main/scala/com/github/plokhotnyuk/jsoniter_scala/core/JsonReader.scala

@@ -2844,13 +2844,17 @@ final class JsonReader private[jsoniter_scala](
       first = Math.max(first - 8, 0)
       var i = last
       val q = 1000000000000000000L
-      while (i >= first) {
-        val m = ByteArrayAccess.getLong(magnitude, i)
-        val p = m * q
-        x += p
+      var m, mq = 0L
+      while ({
+        m = ByteArrayAccess.getLong(magnitude, i)
+        mq = m * q
+        x += mq
         ByteArrayAccess.setLong(magnitude, i, x)
-        x = NativeMath.unsignedMultiplyHigh(m, q) + ((~x & p) >>> 63)
         i -= 8
+        i >= first
+      }) {
+        x = (~x & mq) >>> 63
+        x += NativeMath.unsignedMultiplyHigh(m, q)
       }
     }
     var i = 0