bdiff: don't check border condition in loop
This is pretty much a copy of d500ddae7494, just to a different loop.
The condition `p == plast` (`plast == a + len - 1`) was only true on
the final iteration of the loop. So it was wasteful to check for it
on every iteration. We decrease the iteration count by 1 and add an
explicit check for `p == plast` after the loop.
Again, we see modest wins.
From the mozilla-unified repository:
$ perfbdiff -m 3041e4d59df2
! wall 0.035502 comb 0.040000 user 0.040000 sys 0.000000 (best of 100)
! wall 0.030480 comb 0.030000 user 0.030000 sys 0.000000 (best of 100)
$ perfbdiff 0e9928989e9c --alldata --count 100
! wall 4.097394 comb 4.100000 user 4.100000 sys 0.000000 (best of 3)
! wall 3.597798 comb 3.600000 user 3.600000 sys 0.000000 (best of 3)
The 2nd example throws a total of ~3.3GB of data at bdiff. This
change increases the throughput from ~811 MB/s to ~924 MB/s.
" Vim syntax file
" Language: Mercurial unified tests
" Author: Steve Losh (steve@stevelosh.com)
"
" Place this file in ~/.vim/syntax/ and add the following line to your
" ~/.vimrc to enable:
" au BufNewFile,BufRead *.t set filetype=hgtest
"
" If you want folding you'll need the following line as well:
" let hgtest_fold=1
"
" You might also want to set the starting foldlevel for hgtest files:
" autocmd Syntax hgtest setlocal foldlevel=1
if exists("b:current_syntax")
finish
endif
syn include @Shell syntax/sh.vim
syn match hgtestComment /^[^ ].*$/
syn region hgtestOutput start=/^ [^$>]/ start=/^ $/ end=/\v.(\n\n*[^ ])\@=/me=s end=/^ [$>]/me=e-3 end=/^$/ fold containedin=hgtestBlock
syn match hgtestCommandStart /^ \$ / containedin=hgtestCommand
syn region hgtestCommand start=/^ \$ /hs=s+4,rs=s+4 end=/^ [^>]/me=e-3 end=/^ $/me=e-2 containedin=hgtestBlock contains=@Shell keepend
syn region hgtestBlock start=/^ /ms=e-2 end=/\v.(\n\n*[^ ])\@=/me=s end=/^$/me=e-1 fold keepend
hi link hgtestCommandStart Keyword
hi link hgtestComment Normal
hi link hgtestOutput Comment
if exists("hgtest_fold")
setlocal foldmethod=syntax
endif
syn sync match hgtestSync grouphere NONE "^$"
syn sync maxlines=200
" It's okay to set tab settings here, because an indent of two spaces is specified
" by the file format.
setlocal tabstop=2 softtabstop=2 shiftwidth=2 expandtab
let b:current_syntax = "hgtest"