Fix scala-js#4088: Avoid an Int overflow in BigDecimal.toString(). (#…

…1837)

javalib/src/main/scala/java/math/Conversion.scala

@@ -284,10 +284,10 @@ private[math] object Conversion {
         result = (48 + (prev - v * 10)).toChar + result
       } while (v != 0)
 
-      val exponent = resLengthInChars - currentChar - scale - 1
+      val exponent: Long = resLengthInChars - currentChar - scale.toLong - 1
 
-      if (scale > 0 && exponent >= -6) {
-        val index = exponent + 1
+      if (scale > 0 && exponent >= -6L) {
+        val index = exponent.toInt + 1
         if (index > 0) {
           // special case 1
           result = result.substring(0, index) + "." + result.substring(index)
@@ -299,16 +299,15 @@ private[math] object Conversion {
           result = "0." + result
         }
       } else if (scale != 0) {
-        var result1 = exponent.toString
-        if (exponent > 0)
-          result1 = '+' + result1
-        result1 = 'E' + result1
+        val exponentStr =
+          if (exponent > 0) "E+" + exponent
+          else "E" + exponent
 
         result =
           if (resLengthInChars - currentChar > 1)
-            result(0) + "." + result.substring(1) + result1
+            result.substring(0, 1) + "." + result.substring(1) + exponentStr
           else
-            result + result1
+            result + exponentStr
       }
 
       if (negNumber) '-' + result

unit-tests/src/test/scala/java/math/BigDecimalToStringSuite.scala

@@ -0,0 +1,68 @@
+// Ported from Scala.js original and adapted for Scala Native.
+// BigDecimalToStringTesT.scala, commit 3851c2d, dated: 2020-06-19.
+//     https://raw.githubusercontent.com/scala-js/scala-js/\
+//         83056e39d54c4546a11372add54abb1ece6c5df1/test-suite/\
+//         shared/src/test/scala/org/scalajs/testsuite/\
+//         javalib/math/BigDecimalToStringTest.scala
+
+/*
+ * Scala.js (https://www.scala-js.org/)
+ *
+ * Copyright EPFL.
+ *
+ * Licensed under Apache License 2.0
+ * (https://www.apache.org/licenses/LICENSE-2.0).
+ *
+ * See the NOTICE file distributed with this work for
+ * additional information regarding copyright ownership.
+ */
+
+package java.math
+
+object BigDecimalToStringSuite extends tests.Suite {
+
+  test("testToStringWithCornerCaseScales") {
+    val bigIntOne = BigInteger.valueOf(1)
+
+    assertEquals("1", new BigDecimal(bigIntOne, 0).toString())
+
+    assertEquals("0.01", new BigDecimal(bigIntOne, 2).toString())
+    assertEquals("0.000001", new BigDecimal(bigIntOne, 6).toString())
+    assertEquals("1E-7", new BigDecimal(bigIntOne, 7).toString())
+    assertEquals("1E-2147483647",
+                 new BigDecimal(bigIntOne, 2147483647).toString())
+
+    assertEquals("1E+1", new BigDecimal(bigIntOne, -1).toString())
+    assertEquals("1E+2", new BigDecimal(bigIntOne, -2).toString())
+    assertEquals("1E+15", new BigDecimal(bigIntOne, -15).toString())
+    assertEquals("1E+2147483647",
+                 new BigDecimal(bigIntOne, -2147483647).toString())
+    assertEquals(
+      "1E+2147483648",
+      new BigDecimal(bigIntOne, -2147483648).toString()
+    ) // Scala.js Issue #4088
+
+    val bigInt123 = BigInteger.valueOf(123)
+
+    assertEquals("123", new BigDecimal(bigInt123, 0).toString())
+
+    assertEquals("1.23", new BigDecimal(bigInt123, 2).toString())
+    assertEquals("0.000123", new BigDecimal(bigInt123, 6).toString())
+    assertEquals("0.00000123", new BigDecimal(bigInt123, 8).toString())
+    assertEquals("1.23E-7", new BigDecimal(bigInt123, 9).toString())
+    assertEquals("1.23E-2147483645",
+                 new BigDecimal(bigInt123, 2147483647).toString())
+
+    assertEquals("1.23E+3", new BigDecimal(bigInt123, -1).toString())
+    assertEquals("1.23E+4", new BigDecimal(bigInt123, -2).toString())
+    assertEquals("1.23E+17", new BigDecimal(bigInt123, -15).toString())
+    assertEquals(
+      "1.23E+2147483649",
+      new BigDecimal(bigInt123, -2147483647).toString()
+    ) //  Scala.js Issue #4088
+    assertEquals(
+      "1.23E+2147483650",
+      new BigDecimal(bigInt123, -2147483648).toString()
+    ) //  Scala.js Issue #4088
+  }
+}