RFR: 8313564: Fix -Wconversion warnings in classfile code [v4]

[Coleen Phillimore]

On Thu, 3 Aug 2023 19:47:42 GMT, Dean Long <dlong at openjdk.org> wrote:

>> I put the cast in because prefetch_data_size() returns uint and I'm narrowing it to int which has a lower positive range.  I assume checked_cast would find that.
>
> OK, so you caught it by inspection and are fixing it proactively :-)

Yeah heading off these -Wsign-conversion warnings :)

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PR Review Comment: https://git.openjdk.org/jdk/pull/15111#discussion_r1283734384