Fix overflow conditions in prefetch plugin

[moonchen]

In the prefetch plugin:

1. Specify integer size limitations in README.
2. Specify underflow/overflow behavior in README.
3. Modify evaluate() to handle integer size and under/overflow conditions.
4. Refactor and add unit tests.

This PR addresses #8569.

[masaori335]

@ezelkow1 please add Mo (@moonchen) to the ci list too.

[ywkaras]

I and others are having trouble running the prefetch plugin ( #8216 ). @moonchen can you provide, as an example, a line from your remap.config file? I'd like to write an Au test case for prefetch and run it with a build including this change.

[ywkaras]

Missing end-of-line.

[moonchen]

Thanks. Added an eol.

[ywkaras]

Did you mean 64 not 32?

Also have you tried https://restructuredtext.documatt.com/element/superscript.html ?

[moonchen]

I chose 32-bit operands and 64-bit results here so that addition doesn't ever overflow. That way there doesn't need to be a special rule for handling overflows when adding.

Thanks for pointing out the superscript element. I've changed the exponent to a superscript.

[moonchen]

I and others are having trouble running the prefetch plugin ( #8216 ). @moonchen can you provide, as an example, a line from your remap.config file? I'd like to write an Au test case for prefetch and run it with a build including this change.

I'm testing using these rules:

map http://example.com http://origin.com \
    @plugin=cachekey.so @pparam=--remove-all-params=true \
    @plugin=prefetch.so \
        @pparam=--front=true \
        @pparam=--fetch-policy=simple \
        @pparam=--fetch-path-pattern=/(.*-)(\d+)(.*)/$1{$2+2}$3/ \
        @pparam=--fetch-count=3

Compared to the example in the docs, I added --front=true.

[ywkaras]

Merging this for Mo Chen since he's not yet a committer.

[zwoop]

Cherry-picked to v9.2.x