JDK 11 RFR of JDK-8202563: BigInteger/BigDecimal not immune to overflow, contrary to spec (original) (raw)

joe darcy joe.darcy at oracle.com
Tue May 8 04:47:28 UTC 2018

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Hello,

Over in BigInteger, 2^Integer.MAX_VALUE just isn't as effectively infinite as it used to be. Please review the spec changes and CSR below to clarify that the range of BigInteger is "arbitrarily large" but not "infinite":

JDK-8202563: BigInteger/BigDecimal not immune to overflow, contrary to spec webrev: http://cr.openjdk.java.net/~darcy/8202563.0/ CSR: https://bugs.openjdk.java.net/browse/JDK-8202761

Patch below.

Thanks,

-Joe

--- old/src/java.base/share/classes/java/math/BigInteger.java 2018-05-07 21:39:33.679361845 -0700 +++ new/src/java.base/share/classes/java/math/BigInteger.java 2018-05-07 21:39:33.139361869 -0700 @@ -52,18 +52,15 @@ * and a few other miscellaneous operations. * *

Semantics of arithmetic operations exactly mimic those of Java's integer

- arithmetic operators, as defined in The Java Language Specification.

- arithmetic operators, as defined in The Java™ Language Specification. * For example, division by zero throws an {@code ArithmeticException}, and * division of a negative by a positive yields a negative (or zero) remainder.

- All of the details in the Spec concerning overflow are ignored, as
- BigIntegers are made as large as necessary to accommodate the results of an
- operation. * *
  Semantics of shift operations extend those of Java's shift operators * to allow for negative shift distances. A right-shift with a negative * shift distance results in a left shift, and vice-versa. The unsigned * right shift operator ({@code >>>}) is omitted, as this operation makes
- little sense in combination with the "infinite word size" abstraction

- little sense in combination with the arbitrarily large abstraction * provided by this class. * *
  Semantics of bitwise logical operations exactly mimic those of Java's @@ -84,8 +81,8 @@ * extended so that it contains the designated bit. None of the single-bit * operations can produce a BigInteger with a different sign from the * BigInteger being operated on, as they affect only a single bit, and the

- "infinite word size" abstraction provided by this class ensures that there
- are infinitely many "virtual sign bits" preceding each BigInteger.

- arbitrarily large abstraction provided by this class ensures that conceptually
- there are infinitely many "virtual sign bits" preceding each BigInteger. * *
  For the sake of brevity and clarity, pseudo-code is used throughout the * descriptions of BigInteger methods. The pseudo-code expression @@ -105,13 +102,18 @@ * +2^{{@code Integer.MAX_VALUE}} (exclusive) * and may support values outside of that range. *
- An {@code ArithmeticException} is thrown when a BigInteger
- constructor or method would generate a value outside of the
- supported range.
- * The range of probable prime values is limited and may be less than * the full supported positive range of {@code BigInteger}. * The range must be at least 1 to 2^500000000. * * @implNote

- BigInteger constructors and operations throw {@code ArithmeticException} when
- the result is out of the supported range of

- In the reference implementation, BigInteger constructors and
- operations throw {@code ArithmeticException} when the result is out
- of the supported range of * -2^{{@code Integer.MAX_VALUE}} (exclusive) to * +2^{{@code Integer.MAX_VALUE}} (exclusive). *

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