Björn Steinbrink wrote: > Using ":syn sync fromstart" on platforms where "long" is 64bits wide > breaks the state cache, causing vim to be very very slow on large files. > > How to reproduce: > :syntax on > :help :syn-sync > :syn sync fromstart > <scroll up using j> > > Here's what happens: > > When ":syn sync fromstart" is used, vim sets minlines to MAXLNUM, which > is defined as the largest positive signed 32 bit number, 0x7fffffff. > > When the help buffer is opened, vim jumps to line 3826 and there is > either no valid state yet or it is too far away from this line (I didn't > check which case it is, as it doesn't matter), so in syntax.c:559, we > find that our current state is invalid and thus do: > > syn_sync(wp, lnum, last_valid); > first_stored = current_lnum + syn_block->b_syn_sync_minlines; > > syn_sync() will set current_lnum to 1, so we sync from the start. And > b_syn_sync_minlines is 0x7fffffff. > > Now, on a platform where long is 32bits, the addition happens to > overflow[1], i.e. we get some large negative value, but on a platform > with 64bit "long"s, no such overflow happens and we get a large positive > number. > > Then, a few lines further down, we check whether the current state is > valid, starting with line 583: > > /* If we parsed at least "minlines" lines or started at a valid > * state, the current state is considered valid. */ > if (current_lnum >= first_stored) > > With 32bit longs, first_stored overflowed, so it's negative and the > check always succeeds. With 64bit longs, first_stored is a large > positive number, and the check will (practically) never succeed, so the > state is never stored in the cache. > > The patch below[2] is a quick hack that eliminates the problem, but > spreads knowledge about the MAXLNUM "shortcut" for the fromstart syncing > through the code, so IMHO that's not an acceptable solution, but I > currently lack time and knowledge to come up with anything more useful.
When setting to "minlines" to half of 0x7fffffff it should also work properly. Thus checking for a specific value is only half a solution. I think it will work to check if we start at the first line. Then it's also correct when "minlines" is something like 1000 and displaying around line 500. We can start storing states right away, because it's always correct for line 1. I made a patch that does this, please verify if it works in your situation. -- hundred-and-one symptoms of being an internet addict: 195. Your cat has its own home page. /// Bram Moolenaar -- b...@moolenaar.net -- http://www.Moolenaar.net \\\ /// sponsor Vim, vote for features -- http://www.Vim.org/sponsor/ \\\ \\\ an exciting new programming language -- http://www.Zimbu.org /// \\\ help me help AIDS victims -- http://ICCF-Holland.org /// -- You received this message from the "vim_dev" maillist. Do not top-post! Type your reply below the text you are replying to. For more information, visit http://www.vim.org/maillist.php
