Validate ascii string by ORing all bytes and check if 7-th bit is 0.
Compared with original std::any_of(), which checks ascii string byte
by byte, this new approach validates input in 8 bytes and two
independent streams. Performance is much higher for normal cases,
though slightly slower when string is very short. See table below.
Speed(MB/s) of ascii string validation
+---------------+-------------+---------+
| String length | std::any_of | u64 x 2 |
+---------------+-------------+---------+
| 9 bytes | 1691 | 1635 |
+---------------+-------------+---------+
| 31 bytes | 2923 | 3181 |
+---------------+-------------+---------+
| 129 bytes | 3377 | 15110 |
+---------------+-------------+---------+
| 1039 bytes | 3357 | 31815 |
+---------------+-------------+---------+
| 16385 bytes | 3448 | 47983 |
+---------------+-------------+---------+
| 1048576 bytes | 3394 | 31391 |
+---------------+-------------+---------+
Signed-off-by: Yibo Cai <yibo.cai@arm.com>
Message-Id: <1544669646-31881-1-git-send-email-yibo.cai@arm.com>
422987ab04