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be1a215538
Previously, `mb_check_encoding` did an awful lot of unneeded work. In order to determine whether a string was valid or not, it would convert the whole string into wchar (code points), which required dynamically allocating a (potentially large) buffer. Then it would turn right around and convert that big 'ol buffer of code points back to the original encoding again. Finally, it would check whether any invalid bytes were detected during that long and onerous process. The thing is, mbstring _already_ has machinery for detecting whether a string is valid in a certain encoding or not, and it doesn't require copying any data around or allocating buffers. Better yet, it can fail fast when an invalid byte is found. Why not use it? It's sure a lot faster! Further, the legacy code was also badly broken. Why? Because aside from checking whether illegal characters were detected, it would also check whether the conversion to and from wchars was lossless. But, some encodings have more than one valid encoding for the same character. In such cases, it is not possible to make the conversion to and from wchars lossless for every valid character. So `mb_check_encoding` would actually reject good strings in a lot of encodings!