The following is from README
gpicker is a program that allows you to quickly and conveniently pick file in a (possibly very large) project. You type significant letters of file name (typically from the start of words) and gpicker provides you with a list of files you most likely mean to pick. The program filters and orders project's list of files in real-time as you type.
It was inspired by class finding facility of IntelliJ IDEA and 'Command-T' feature of TextMate, but it's in many ways much better. It is language-agnostic and supports matching directory names too. Read on for details.
It is usable as a standalone program, but it was created to be used by editors/IDEs. Currently only Emacs intergration is provided. See comments on top of gpicker.el for installation notes. This README describes general usage concepts.
To place 'correct' matches on top gpicker uses sophisticated scoring heuristics. Scoring is implemented by efficient dynamic programming algorithm which makes filtration and ordering very fast. The scoring details are described below.
Don't judge gpicker's performance by first run. gpicker scans project for list of files on every start. This can take a while on first run. But subsequent runs will hit OS's directory entries cache and will start almost instantly.
Real-time filtration should be snappy on most, but largest projects. At least if your CPU is not very old.
When I want to pick 'vendor/rails/activerecord/lib/active_record/base.rb' inside rails project I can type 'ba' or 'bas'. But it won't be displayed on top, because rails has several files named base.rb in different directories. I can type 'ar/ba' (or even 'ar/b'). This will match 'ar' against directory name and 'ba' against basename and will place 'correct' file on top.
To pick source of java.lang.ClassLoader class inside openjdk I can try 'cload'. There a many matches and correct file is not in top 5 (but it's in top 10). I can try placing emphasis on start of words by capitalizing them - 'cLoa' or 'CLoa'. But that removes only one extra match. I can add directory name pattern to better convey my intention. 'lan/cLo' is sufficient to find correct file on second place. It can be selected via arrow keys now. And 'cl/la/cLo' (added another part of directory - 'classes') or 'lan/cLo.j' (added extension) is enough to place it first. 'clloderj' works too. Notice skipped 'a' from 'loader'.
There are two ways to emphasize start of words. One is capitalizing first letters. 'aRe' or 'AR' will give large score to 'active_record', 'active-record', 'active.record' and 'ActiveRecord'.
Second way is placing matching delimiters before first letter. 'b.r' will give large score for 'base.rb', because match of 'r' after delimiter is considered start of the word. Delimiters '_' and '-' are interchangeable. So association_proxy.rb can be matched with 'a-pro' and with 'a_pro' (and with 'aPro' of course). That was done because '-' is easier to type.
Empty basename patterns can be used to browse list of files in some directory. For example 'are/con-ad/' can be used to see contents of vendor/rails/activerecord/lib/active_record/connection_adapters/.
Only matching entries pass through filter. In simple words, there is a match between given pattern and name if and only if it is possible to transform name to pattern by removing characters from it without changing order of remaining characters.
Matching is case insensitive, though capital letters both in pattern and in name are additionally treated as word starts. Letters after delimiters also count as word starts.
Smart ordering of matches is based on matches' scores. Scoring rules are quite simple. Each character match is given some score and those are summed for total match score. Match on word start is given 0x100000 points if matching pattern character is on word start too, and 0x201 points otherwise. Match is given 0x400 points if it's adjacent to previous match. And all other matches are given 0 points.
The idea is that 'proper' word start matches are most precious. All other matches score significantly less. Among those substring matches score about twice as much as non-proper word start matches. And completely wild matches do not score at all.
If there are several matches for given name then the scoring algorithm picks leftmost (or rightmost, for directory name matches) with maximal score.
Directory names and basenames are scored separately and directory name score is considered only when basename scores are equal.
For typically short patterns it's not unlikely to have a group of names with maximal score. So great attention is given to ordering names with equal scores. Current ordering heuristic takes compactness of match into account (minimization of last matching character index) and length of names. See code in filtration.c for exact details.