openjdk-jdk11

That throws an exception though, while this code is trying to return 0. The java "fix" would be to add a charAtOrDefault(), but that doesn't seem to exist. The source of charAt is also interesting because it manually bounds checks while the array access into the underlying char[] has its own bounds check. I'm not sure why having the separate exception is better than letting the array access throw directly? https://github.com/AdoptOpenJDK/openjdk-jdk11/blob/19fb8f93c...

For reference, this is what String.substring(int, int) does[1] in Java: public String substring(int beginIndex, int endIndex) { int length = length(); checkBoundsBeginEnd(beginIndex, endIndex, length); ... Where checkBoundsBeginEnd[2] does: static void checkBoundsBeginEnd(int begin, int end, int length) { if (begin < 0 || begin > end || end > length) { throw new StringIndexOutOfBoundsException( "begin " + begin + ", end " + end + ", length " + length); } } (as it should, in my opinion). [1] https://github.com/AdoptOpenJDK/openjdk-jdk11/blob/f0ef2826d... [2] https://github.com/AdoptOpenJDK/openjdk-jdk11/blob/f0ef2826d...

I'm no Java ninja, but a few things jump out of https://github.com/AdoptOpenJDK/openjdk-jdk11/blob/19fb8f93c... : - at least one heap allocation for every line. After it finds the EOL it first uses 'new String' followed by '.toString() - the C++ version will almost certainly be backing on to memchr() behind the scenes, which will be using SIMD instructions where it makes sense (e.g. large enough scan size, probably true in this case). the Java version is a manual bytewise-coded loop. - the C++ version is reusing its output buffer, no reallocations assuming the same string length or less No idea about encodings in Java, maybe that is playing a role too