fix: compression edge case

[dictcp]

the condition to do compression is incorrent since previous refactoring. according to docs

https://secure.php.net/manual/en/memcached.configuration.php#ini.memcached.compression-factor

Store compressed if: plain_len > comp_len * factor

https://github.com/php-memcached-dev/php-memcached/blob/master/memcached.ini#L93

store compressed if: plain_len > comp_len * factor

hence, the condition (to early exit, without compression) should be
if (ZSTR_LEN(payload) < (compressed_size * compression_factor))

---

PR includes

• fix to the compression_factor formula (whether to compress or not),
• correctly unset MEMC_VAL_COMPRESSION_{FASTLZ,ZLIB} flags flags properly when plain-text is sent

[dick9gag]

@krakjoe @mkoppanen

could you help to review the PR and accept it if it looks good to you?

it fixes some problem due to incorrect compression flag set

[sodabrew]

@dictcp Could I ask you to rebase this against master, as the php7 branch has been merged?

[dictcp]

@sodabrew rebased and target to merge to master branch.

[sodabrew]

Thanks for the rebase! The doc link says

store uncompressed if plain_len > comp_len * factor

But the code is:
if (ZSTR_LEN(payload) < (compressed_size * MEMC_G(compression_factor)))

One of those two expressions has the comparison operator flipped!?

[dictcp]

it should be

Store compressed if: plain_len > comp_len * factor

https://secure.php.net/manual/en/memcached.configuration.php#ini.memcached.compression-factor

store compressed if: plain_len > comp_len * factor

https://github.com/php-memcached-dev/php-memcached/blob/master/memcached.ini#L93

hence, the condition (to early exit, without compression) should be
if (ZSTR_LEN(payload) < (compressed_size * compression_factor))

[sodabrew]

Nit: should your change be payload <= compressed * factor?

Could I bug you to update the docs in this PR as you've described?

[dictcp]

@sodabrew push commit and update the description of the PR. sounds good to you?
(no sure what you means by "update the docs", do you mean I should update the ChangeLog, or leaving a good description on on PR sounds good)

[sodabrew]

Thank you!