Calculates the sha1 hash of filename using the US Secure Hash Algorithm 1, and returns that hash. The hash is a 40-character hexadecimal number. Upon failure, FALSE is returned. If the optional raw_output is set to TRUE, then the sha1 digest is instead returned in raw binary format with a length of 20.
Note: The optional raw_output parameter was added in PHP 5.0.0 and defaults to FALSE
See also sha1(), crc32(), and md5_file()