## Roadmap

See the sections below for details

* Tests for simple solver
* Extend cube and moves to include centers
* More complex optimal solvers, pruning tables
* Benchmarks
* Multithreading (build-time option number of threads)
* Other optimizations
* NISS
* Move manipulation utilities
* Coordinate solvers and other steps
* More output formats
* Adapters for other languages (at least python)
* More documentation (or keep all in cube.h?)
* Rename to libnissy
* Release 1.0

## Solving

### Simple (slow, light) solver

* Decide on API for solve() (see above)
* solve generic becomes private, use cube_fast_t instead of cube_t
* write simple solver based on generic
* tests: solve full cube (max 7-8 moves?)
* benchmarks

### Coordinates

TODO: specify in the comments that coordinates return 0 if solved

* [done] eo
* co
* ep
* epsep
* cp
* cpsep
* cphtr

What about symcoord?

### More solvers

* solve_light: first based on solve_generic, then optimize; benchmark
  to see up to what length it works best (7 moves? 10 moves?)

### Implement the following solvers:

* Slow: basic solver without any table.
* H48: one-bit-per-entry table + fallback, 48 symmetries and so on.
  See planner.
* nxopt31: mostly for comparison.
* other nxopt solvers: make generic and take the type as parameter.
* Step solver: take a coordinate function and a moveset as a parameter.

### New method:

* 48 symmetries, cocsep (or chtr, or similar) + epsep + some EO
* 1 bit per entry + fallback
* store necessary stuff (e.g. ttrep) all interleaved in the same table

### Other considerations:

* Reconsider going corners-first, so there is no need to sumco()

### Pruning tables

* ptable should contain some extra data at the beginning:
  an integer (size)
  a checksum
  some summary info, maybe even in text form

## Optimizations

### General things

* Trans: don't do full compose, for some trans composing perm is enough.
  Split out sumco() as a separate function and refactor, optimize.
* Use multi-move (up to 4/5 moves at once)
* CO is the worst part of moving, transforming and inverting. Try basing
  everything on representing the cube without CO and apply it only at the
  end to check that it is actually solved.
* see if vcube's method to flip all corners is better
* find a better way for computing the inverse?
* Improve avx2 instructions in general

### Threading

* THREADS build time option for the number of threads. If set to one,
  do not include any threading library or code. Try detecting at build
  time, or set to a sane default (e.g. 8? 16?) for generic builds.
* pthread or threads.h? I am more familiar with pthread, but threads.h
  is standard (from C11, so it requires switching to it from C99).
  Does using threads.h help in any way (e.g. building on Windows)?

## Improvements and other things

* Rename to libnissy (prefix public functions with nissy_?)
* add centers (and moves...)
* for CO: move to bits 5 and 6, no need for padding bit
* manipulate move sequences (invert, unniss, cleanup, mirror / transform...)
* NISS: Add mask to moves (e.g. U | NISS where NISS = 32 or something);
  adapt readmoves and writemoves.
* Consider adding centers and other moves (for avx2: centers in the
  same lane as corners, numbered from 9 to 14)
* More I/O:
  nissy
  ascii art (color = 1 letter)
  twizzle binary https://www.experiments.cubing.net/cubing.js/spec/binary/
  reid?
* print ptables (or layout data in such a way that can be printed
  easily, e.g. first bytes are null-terminated strig and can be
  printed by user)

## "Front-end"

* Write adapter code for other languages:
  python
  hare
  rust, go
  dart ffi, js
  java
* add also example code (e.g. an optimal solver) in examples/

## More documentation?

* Add documentation comments inside cube.c?
* Copy this to cube.c

Transformations can be either simple rotations or a rotation composed
with a mirroring.  A composed rotation + mirror is obtained by applying
the corresponding rotation to the solved cube mirrored along the M plane.

For example, to apply the transformation RBm (mirrored RB) to a cube C:
	1. Apply a mirror along the M plane to the solved cube
	2. Rotate the mirrored cube with z' y2
	3. Apply the cube C to the transformed solved cube
	4. Apply the transformations of step 1a and 1b in reverse