Description:
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utf8_decode() outputs a random character when supplied with bad input.

When invalid sequences are added, utf8_decoded() usually replace the sequence with the character "?". But when a lonely highbit character is present in the end the output seem to be a random character.


Reproduce code:
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for($a=0;$a<20;$a++)printf("%02x ",utf8_decode(chr(0xE0)));


Expected result:
----------------
3f 3f 3f 3f 3f 3f 3f 3f 3f 3f 3f 3f 3f 3f 3f 3f 3f 3f 3f 3f

(utf8_decode() returns a question mark)

Actual result:
--------------
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
or
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09
or
05 05 05 05 05 05 05 05 05 05 05 05 05 05 05 05 05 05 05 05
or
02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02
or some other random value

It seem to differ more with individual runs:

$ for a in `seq 1 20`; do php -r 'printf("%02x ",utf8_decode(chr(0xE0)));';
done
08 00 00 02 00 00 00 00 00 05 00 00 00 05 00 00 07 00 09 00