On Thu, 29 Sep 2022 22:14:24 GMT, Joe Darcy <da...@openjdk.org> wrote:
> While the floating-point == operation is *not* an equivalence relation, there
> are useful equivalence relations that can be defined over floating-point
> values. Text is added to java.lang.Double to discuss and name those relations.
src/java.base/share/classes/java/lang/Double.java line 157:
> 155: * Under this relation, {@code +0.0} and {@code -0.0} are distinguished
> 156: * from each other and every bit pattern encoding a NaN is distinguished
> 157: * form other bit patterns encoding a NaN.
s/form/from
src/java.base/share/classes/java/lang/Double.java line 180:
> 178: * of equivalence to test the behavior of {@linkplain StrictMath math
> 179: * libraries}.
> 180: * </dd>
This list deserves to include the not-quite-equivalence relation `==`. Suggest:
- numerical equivalence
- {@code +0.0} and {@code -0.0} are equivalent to each other.
- infinite numbers of the same sign are equivalent to each other
The two floating point numbers represent the same mathematical finite value or
signed infinity.
Expressions implementing this ER include `x == y`, `x > y | x < y`, etc.
Numerical equivalence does not apply to NaN, as NaN violates the reflexive
property required of all equivalences, but on the domain of all non-NaNs,
numerical equivalence is in fact an equivalence relation.
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PR: https://git.openjdk.org/jdk/pull/10498
