I’m writing a routine that takes a string and formats it as quoted printable. And it’s got to be as fast as possible. My first attempt copied characters from one stringbuffer to another encoding and line wrapping along the way. Then I thought it might be quicker to just modify the original stringbuffer rather than copy all that data which is mostly identical. Turns out the inserts are far worse than copying, the second version (with the stringbuffer inserts) was 8 times slower, which makes sense, as it must be moving a lot of memory.
What I was hoping for was some kind of gap buffer data structure so the inserts wouldn’t involve physically moving all the characters in the rest of the stringbuffer.
So any suggestions about the fastest way to rip through a string inserting characters every once in a while?
Suggestions to use the standard mimeutils library are not helpful because I’m also dot escaping the string so it can be dumped out to an smtp server in one shot.
So taking the advice of some of the other answers here I’ve been writing many versions of this function, seeing what goes quickest and for future reference if anybody can gain from what I found:
1) The slowest: stringbuffer.append() but we knew that.
2) Almost twice as fast: stringbuilder.append(). locks are very expensive it seems.
3) another 20% faster is…. copying from one char[] to another.
4) and finally, coming in three times faster than even that… a JNI call to the exact same code compiled in C that copies from one char array to another.
You may consider #4 cheating, but cheaters win. It is by far the fastest way to go.
There is a risk of the GetCharArrayElements call causing the java char array to be copied so it can be handed to the C program, but I can’t tell if that’s happening, and it’s still wicked fast compared to any java implementation.