While it was dealing with C strings, some years back I was curious about Firefox's poor Sunspider showing, so I dove into both the benchmark and the code, deter

While it was dealing with C strings, some years back I was curious about Firefox's poor Sunspider showing, so I dove into both the benchmark and the code, determining that- a) SunSpider was overwhelmingly a benchmark measuring string concatenation performance. b) Firefox had slow string concatenation. The solution to b) was trivial -- whenever Firefox saw that you were doing str = str + something, it would realloc str to the new length of len(str)+len(something)+1 and then strcpy something to the tail of str. By changing the code slightly to trade a relatively small amount of memory (in most situations), making every realloc size to the next power-of-two greater than the new combined length, this improved SunSpider performance 20x+ because the vast majority of concatenations could be done in place.