RFR: 8368349: Add library notes discussing abs and IEEE 754 operations

[Raffaello Giulietti]

On Tue, 23 Sep 2025 03:02:32 GMT, Joe Darcy <darcy at openjdk.org> wrote:

> Add apiNote linking {Math, StrictMath}.abs to the IEEE 754 abs operation.

I checked 754-2008, which requires a 0 sign bit, and 754-1985 (reaffirmed in 1990), which in the annex on recommended functions reads

> Copysign(x,y) returns x with the sign of y. Hence, abs(x) = copysign(x,1.0), even it x is NaN.

So it seems that hardware that does not behave this way is not compliant.
I'm curious what other platforms specify.

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PR Comment: https://git.openjdk.org/jdk/pull/27443#issuecomment-3324890959