RFR: 8346914: UB issue in scalbnA

[Fredrik Bredberg]

On Thu, 5 Jun 2025 13:54:49 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> I'm suprised that is even valid TBH. It strikes me as a numerical oxymoron.
>
>>"If the destination type is unsigned, the resulting value is the least unsigned integer congruent to the source integer (modulo 2n where n is the number of bits used to represent the unsigned type). [ Note: In a two’s complement representation, this conversion is conceptual and there is no change in the bit pattern (if there is no truncation). —end note ]
> 
> So this is OK.

The hard part for me is that when I see `-54u` , I need to make sure it's return type is `unsigned`, which is not immediately obvious to me. Reading what the standard say about the built-in unary minus operator I find: _"The type of the result is the type of the promoted type of expression."_ Which means that the return type of `-54u` really is `unsigned`. But I do agree with David, it looks like a numerical oxymoron.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25656#discussion_r2129118383