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

[joe darcy]

On 5/7/2018 10:45 PM, Martin Buchholz wrote:
> Thanks for doing this - wordsmithing is hard.
>
> Maybe
>
> The unsigned
> * right shift operator ({@code >>>}) is omitted, as this operation 
> only makes sense with a fixed word size.

How about

The unsigned right shift operator ({@code >>>}) is omitted since this 
operation only makes sense for a fixed sized word and not for a 
representation conceptually having an infinite number of leading virtual 
sign bits.

-Joe

>
> On Mon, May 7, 2018 at 9:47 PM, joe darcy <joe.darcy at oracle.com 
> <mailto:joe.darcy at oracle.com>> wrote:
>
>     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/
>     <http://cr.openjdk.java.net/%7Edarcy/8202563.0/>
>         CSR: https://bugs.openjdk.java.net/browse/JDK-8202761
>     <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.
>       *
>       * <p>Semantics of arithmetic operations exactly mimic those of
>     Java's integer
>     - * arithmetic operators, as defined in <i>The Java Language
>     Specification</i>.
>     + * arithmetic operators, as defined in <i>The Java™ 
>     Language Specification</i>.
>       * 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.
>       *
>       * <p>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.
>       *
>       * <p>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.
>       *
>       * <p>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<sup>{@code Integer.MAX_VALUE}</sup> (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<sup>500000000</sup>.
>       *
>       * @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<sup>{@code Integer.MAX_VALUE}</sup> (exclusive) to
>       * +2<sup>{@code Integer.MAX_VALUE}</sup> (exclusive).
>       *
>
>
>