Test string:

Contrary to popular belief, Lorem Ipsum is not simply random text. It has roots in a piece of classical Latin literature from 45 BC, making it over 2000 years old.

PHP: str_slice($s)            -> Contrary to popular belief, Lorem Ipsum is not simply random text. It has roots in a piece of classical Latin literature from 45 BC, making it over 2000 years old.
PHP: str_slice($s, 0, 0)      -> ""
PHP: str_slice($s, 1, 0)      -> ""
PHP: str_slice($s, -1, 0)     -> ""
PHP: str_slice($s, 1, 1)      -> ""
PHP: str_slice($s, -1, -1)    -> ""
PHP: str_slice($s, 0, -50)    -> Contrary to popular belief, Lorem Ipsum is not simply random text. It has roots in a piece of classical Latin lit
PHP: str_slice($s, 0, 50)     -> Contrary to popular belief, Lorem Ipsum is not sim
PHP: str_slice($s, 0, -10000) -> ""
PHP: str_slice($s, 0, 10000)  -> Contrary to popular belief, Lorem Ipsum is not simply random text. It has roots in a piece of classical Latin literature from 45 BC, making it over 2000 years old.
PHP: str_slice($s, 50)        -> ply random text. It has roots in a piece of classical Latin literature from 45 BC, making it over 2000 years old.
PHP: str_slice($s, 100, -40)  -> cal Latin literature fr
PHP: str_slice($s, -100, -30) -> xt. It has roots in a piece of classical Latin literature from 45 BC, 
PHP: str_slice($s, 0, 2)      -> Co
PHP: str_slice($s, 0, -2)     -> Contrary to popular belief, Lorem Ipsum is not simply random text. It has roots in a piece of classical Latin literature from 45 BC, making it over 2000 years ol
PHP: str_slice($s, 3, 4)      -> t
PHP: str_slice($s, 2)         -> ntrary to popular belief, Lorem Ipsum is not simply random text. It has roots in a piece of classical Latin literature from 45 BC, making it over 2000 years old.
PHP: str_slice($s, -2)        -> d.
PHP: str_slice($s, 2, -2)     -> ntrary to popular belief, Lorem Ipsum is not simply random text. It has roots in a piece of classical Latin literature from 45 BC, making it over 2000 years ol
PHP: str_slice($s, -5, -2)    ->  ol
PHP: str_slice($s, -5, 7)     -> ""
PHP: str_slice($s, -5, -7)    -> ""

Performance tests:

PHP: str_slice($s)            -> 0.004053 ms
PHP: str_slice($s, 0, 0)      -> 0.001907 ms
PHP: str_slice($s, 1, 0)      -> 0.001907 ms
PHP: str_slice($s, -1, 0)     -> 0.002861 ms
PHP: str_slice($s, 1, 1)      -> 0.004053 ms
PHP: str_slice($s, -1, -1)    -> 0.002861 ms
PHP: str_slice($s, 0, -50)    -> 0.002861 ms
PHP: str_slice($s, 0, 50)     -> 0.003099 ms
PHP: str_slice($s, 0, -10000) -> 0.004053 ms
PHP: str_slice($s, 0, 10000)  -> 0.002861 ms
PHP: str_slice($s, 50)        -> 0.003099 ms
PHP: str_slice($s, 100, -40)  -> 0.004053 ms
PHP: str_slice($s, -100, -30) -> 0.004053 ms
PHP: str_slice($s, 0, 2)      -> 0.002861 ms
PHP: str_slice($s, 0, -2)     -> 0.003099 ms
PHP: str_slice($s, 3, 4)      -> 0.002861 ms
PHP: str_slice($s, 2)         -> 0.003099 ms
PHP: str_slice($s, -2)        -> 0.003099 ms
PHP: str_slice($s, 2, -2)     -> 0.003815 ms
PHP: str_slice($s, -5, -2)    -> 0.004053 ms
PHP: str_slice($s, -5, 7)     -> 0.003099 ms
PHP: str_slice($s, -5, -7)    -> 0.004053 ms
PHP: str_slice Total Time     -> 0.07176ms