Fix #4870: Handle large (pos and neg) counts in BigInteger.shift{Left,Right}.

sjrd · sjrd · commit baaf8c9bf430 · 2023-05-26T12:38:48.000+02:00
diff --git a/javalib/src/main/scala/java/math/BigInteger.scala b/javalib/src/main/scala/java/math/BigInteger.scala
@@ -130,6 +130,11 @@ object BigInteger {
       throw new IllegalArgumentException(errorMessage)
   }
 
+  private[math] def checkRangeBasedOnIntArrayLength(byteLength: Int): Unit = {
+    if (byteLength < 0 || byteLength >= ((Int.MaxValue + 1) >>> 5))
+      throw new ArithmeticException("BigInteger would overflow supported range")
+  }
+
   @inline
   private[math] final class QuotAndRem(val quot: BigInteger, val rem: BigInteger) {
     def toArray(): Array[BigInteger] = Array[BigInteger](quot, rem)
@@ -668,13 +673,13 @@ class BigInteger extends Number with Comparable[BigInteger] {
   def shiftLeft(n: Int): BigInteger = {
     if (n == 0 || sign == 0) this
     else if (n > 0) BitLevel.shiftLeft(this, n)
-    else BitLevel.shiftRight(this, -n)
+    else BitLevel.shiftRight(this, -n) // -n is interpreted as unsigned, so MinValue is fine
   }
 
   def shiftRight(n: Int): BigInteger = {
     if (n == 0 || sign == 0) this
     else if (n > 0) BitLevel.shiftRight(this, n)
-    else BitLevel.shiftLeft(this, -n)
+    else BitLevel.shiftLeft(this, -n) // -n is interpreted as unsigned, so MinValue is fine
   }
 
   def signum(): Int = sign
diff --git a/javalib/src/main/scala/java/math/BitLevel.scala b/javalib/src/main/scala/java/math/BitLevel.scala
@@ -220,10 +220,11 @@ private[math] object BitLevel {
    *  @return
    */
   def shiftLeft(source: BigInteger, count: Int): BigInteger = {
-    val intCount: Int = count >> 5
+    val intCount: Int = count >>> 5 // interpret count as unsigned to deal with -MinValue
     val andCount: Int = count & 31
     val offset = if (andCount == 0) 0 else 1
     val resLength: Int = source.numberLength + intCount + offset
+    BigInteger.checkRangeBasedOnIntArrayLength(resLength)
     val resDigits = new Array[Int](resLength)
     shiftLeft(resDigits, source.digits, intCount, andCount)
     val result = new BigInteger(source.sign, resLength, resDigits)
@@ -298,7 +299,7 @@ private[math] object BitLevel {
    *  @return
    */
   def shiftRight(source: BigInteger, count: Int): BigInteger = {
-    val intCount: Int = count >> 5
+    val intCount: Int = count >>> 5 // interpret count as unsigned to deal with -MinValue
     val andCount: Int = count & 31 // count of remaining bits
 
     if (intCount >= source.numberLength) {
diff --git a/test-suite/shared/src/test/scala/org/scalajs/testsuite/javalib/math/BigIntegerOperateBitsTest.scala b/test-suite/shared/src/test/scala/org/scalajs/testsuite/javalib/math/BigIntegerOperateBitsTest.scala
@@ -1029,6 +1029,19 @@ class BigIntegerOperateBitsTest {
     assertEquals(-1, result.signum())
   }
 
+  @Test def testShiftsWithLargeCounts_Issue4870(): Unit = {
+    val aNumber = new BigInteger(-1, Array[Byte](0, -82, 127, 15, 76, -97, 13, 30, 30))
+
+    assertThrows(classOf[ArithmeticException], aNumber.shiftLeft(Int.MaxValue))
+    assertThrows(classOf[ArithmeticException], aNumber.shiftRight(Int.MinValue))
+    assertThrows(classOf[ArithmeticException], aNumber.shiftRight(Int.MinValue + 1))
+
+    val minusOne = BigInteger.ONE.negate()
+    assertEquals(minusOne, aNumber.shiftRight(Int.MaxValue))
+    assertEquals(minusOne, aNumber.shiftLeft(Int.MinValue))
+    assertEquals(minusOne, aNumber.shiftLeft(Int.MinValue + 1))
+  }
+
   @Test def testTestBitException(): Unit = {
     val aBytes = Array[Byte](-1, -128, 56, 100, -2, -76, 89, 45, 91, 3, -15, 35, 26)
     val aSign = 1
