The engine of Nissy, including the H48 optimal solver

Warning: this library is work in progress, breaking changes can happen without notice.

This repository contains the core functionality for future versions of nissy.

H48 is an experimental Rubik’s cube solver. It is heavily inspired by nxopt and vcube, but it uses a different set of pruning tables that were developed independently.

Building

First run the configuration script to detect the system configuration. This is going to select a C compiler and architecture-specific optimizations.

$ ./configure.sh

These settings can be overridden, for example:

$ THREADS=3 CC=gcc ./configure.sh   # Use 3 threads and compile with gcc

All the configuration-time options are described in the configure.sh script.

Once the configuration is done, you can build with make

$ make

Running tests

This project includes a suite of “unit” test. They can be run with:

$ make test

To run only a subset of the tests, set the TEST variable to a regular expression that matches only the name of the tests you want to run:

$ TEST=coord make test

Each subfolder of the test folder contains a test. A test can consist of multiple test cases (.in files). Running a test means compiling and running the corresponding test against each test case. When a test case is run, the .in file is read a the output of the program is compared to the corresponding .out filei using diff(1). If the two differ, the difference is printed out and no other test is run.

The results of the last test case run is saved in test/last.out (standard output, the results compared with the .out files) and test/last.err (standard error).

Tests are always run in debug mode: this means that optimizations are disabled and some extra logging is enabled.

See the test folder and test/test.sh for details.

Running “tools”

In the tools folder there are some small programs that test various functionality of the H48 library. They work similarly to test, but they are not run in debug mode by default.

To run a tool you must select it with the environment variable TOOL. For example the command:

TOOL=stats make tool

Will run the statstablesh48 tool.

To pass some arguments to a tool, use the TOOLARGS variable:

TOOL=gendata TOOLARGS="h48 0;2;20" make tool

Like for tests, the value of the TOOL variable can be any regular expression matching the name of the tool. Unlike tests, one and only one tool will be selected for each run. The content of the TOOLARGS variable is used directly as command line arguments for the chosen tool.

Each tool run is automatically timed, so these tools can be used as benchmark. The output as well as the time of the run are saved to a file in the tools/results folder.

To build and run a tool in debug mode, use make debugtool.

Command-line interface

The shell folder contains the code for a rudimentary shell that can be used to run commands manually. The user experience in not amazing, as the commands require quite verbose options.

To build the shell run:

$ make shell

This will create an executable called run. Optionally, you can run some tests:

$ make shelltest

Then you can for example get a cube from a sequence of moves:

$ ./run frommoves -moves "R' U' F"
JLQWSVUH=ZLCUABGIVTKH=A

The cube format is meant to be easy to copy-paste and read for the software, but not necessarily intuitive for the user. See below for a detaileed description.

You can also get a random cube

$ ./run randomcube
WDSQREVX=VBKYDUCJXWAb=A

To solve a cube you can use:

$ ./run solve -solver h48h0k4 -n 1 -M 4 -cube "JLQWSVUH=ZLCUABGIVTKH=A"
F' U' R

Or alternatively:

$ ./run solve_scramble -solver h48h0k4 -n 1 -M 4 -moves "R' U' F"
F' U' R

For a full list of available command, use ./run help.

Using this software as a library

This tool has been developed as a library, so it can be easily included in other programs. For this reason, some bindings for languages other than C are available.

The API is documented in the public header file src/nissy.h.

C

To use this in a C project, simly include src/nissy.h. The tools in the tools/ folder are a good example for how to use this.

NOTE: this project is developed using the C11 standard. If you are using an older version of C, you can write your own header file.

C++

The cpp folder contains a C++ header nissy.h (C++20 standard) and an implementation file nissy.cpp. This interface wraps the calls to the C functions in an object-oriented C++ interface for more convenient use.

The cpp/examples folder contains some examples for how to use this interface. You can build them with e.g.

g++ -std=c++20 cpp/nissy.cpp cpp/examples/solve_h48h3k2.cpp nissy.o

NOTE: If you prefer to use a C-style API, you’ll have to write your own header, similar to the extern "C" {} block at the top of cpp/nissy.cpp. The C header src/nissy.h cannot be compiled as C++, as it uses features of C that are not compatible with it.

Python

The python folder contains a Python module. The API provided by this module follows the C API quite closely, except its functions sometimes return strings instead of writing to char * buffers.

To build the Python module you need the Python development headers installed. You can check this from the output of ./configure.sh:

$ ./configure.sh
...
Python3 development libraries: version 3.12

Then to build the module:

$ make python

And to import it

$ python                                  # In the main folder
>>> import nissy_python_module as nissy   # In the python shell

From here you can call the library functions directly, for example:

>>> nissy.applymoves('ABCDEFGH=ABCDEFGHIJKL=A', "R U R' U'")
'WFCDERQH=AECDIFGHBJKL=A'

The python/examples folder contains some examples, that you can run for example with:

$ python python/examples/solve.py

You can access the documentation for the Python module from within a Python interpreter with help(nissy). Cross-check this documentation with the comments in nissy.h for more details.

NOTE: Support for the Python module is still rudimentary.

Cube format

This format is a “base 32” encoding of the cube. It is not meant to be human-readable, but it is compact while still being plain text. Each piece, including the orientation value, is encoded as a number from 0 to 31, and this number is then converted to an uppercase letter (0-26) or to a lowercase letter (27-31).

The format looks like this:

cccccccc=eeeeeeeeeeee=r

Where the first 8 characters represent the corner, the 12 characters after the first 12 represent the edges and the last character represents the orientation of the cube with respect to the base orientation.

Edges are numbered as follows (see also constants.h):

UF=0 UB=1 DB=2 DF=3 UR=4 UL=5 DL=6 DR=7 FR=8 FL=9 BL=10 BR=11

If the edge is misoriented with respect to the F/B axis, the value is increased by 16.

Corners are numbered as follows:

UFR=0 UBL=1 DFL=2 DBR=3 UFL=4 UBR=5 DFR=6 DBL=7

If the corner is twisted clockwise with respect to the U/D axis orientation, the value is increased by 8. If it is twisted counter-clowsie, the value is increased by 16.

The orientations of the cube are numbered as follows, where e.g. “RB” means that the R face in on top and the B face is on front:

UF=0  UR=1  UB=2  UL=3
DF=4  DR=5  DB=6  DL=7
RF=8  RD=9  RB=10 RU=11
LF=12 LD=13 LB=14 LU=15
FD=16 FR=17 FU=18 FL=19
BD=20 BR=21 BU=22 BL=23

In this format, the solved cube looks like this:

ABCDEFGH=ABCDEFGHIJKL=A

The cube after the move Fw looks like this:

ANCPETGR=AbaDEFGHIJRS=L

A cube in B32 format is always 23 characters long (24 if the terminating null character is included).