On Thu, Sep 10, 2020 at 08:17:32AM -0700, Junio C Hamano wrote: > Junio C Hamano <gitster@xxxxxxxxx> writes: > > > Of course none of the above becomes unnecessary if we scan the whole > > string for SP before the main loop in quote-c-style-counted, but the > > function was written to process the input in a single pass and such > > a change defeats its design. If we need to do it in two passes, we > > can have the caller do so anyway, at least for now. That thinking > > lead to the final organization of the series, with two steps that > > used to be preparatory for passing the flag down thru to the bottom > > layer rebased out as a discardable appendix at the end. > > Actually, this made me realize that another variant is possible. > It might be easier to read, or it might not. Since I cannot tell > without actually writing one, let's see ... Vger seems to be delivering slowly and out-of-order the last day or two, so I got rather confused to receive this after seeing your v2. :) > I don't know if this is easier to follow or not. I do think so > right now but that is only because it is still fresh in my brain. I do think it is easier to read than the original. One minor nit with your analysis, though: the current code is actually two-pass already. One pass finds the next quoted character, but then we have to take another pass to copy it into place. That second pass can be done with a memcpy(), which helps. If you know you are quoting, you can do a true single-pass character-by-character. But of course part of our task is to find out _if_ we are quoting. And even if that were not the case, on modern processors it is not always true that single-pass is going to be faster. This code is definitely not such a hot-spot that it's worth doing that kind of micro-optimization. Aside: We _do_ have spots where that is not true. When I looked at replacing xdiff's hash the sticking point was that we compute the newlines _and_ hash in a single pass. Most "fast" hash functions are optimized to take bigger sequences of data, but splitting out the newline-finding eliminated any gains. -Peff
