node binding for Yuta Mori's libdivsufsort

This library provides a simple and an efficient C API to construct a suffix array and a Burrows-Wheeler transformed string from a given string over a constant-size alphabet. The algorithm runs in O(n log n) worst-case time using only 5n+O(1) bytes of memory space, where n is the length of the string.

See: https://github.com/y-256/libdivsufsort

CircleCI: Travis: Deps:

var divsufsort = require('divsufsort').divsufsort,
    divbwt = require('divsufsort').divbwt;

var lodash = require('lodash'),
    assert = require('assert');

/*
  Suffix array construction
 */
var t = new Buffer('abracadabra'), 
    sa = new Buffer(4 * t.length);  // Must be >= 4x input length

// "sa" receives the suffix array, packed as 32-bit integers.  Will throw if 
// anything goes wrong.  
divsufsort(t, /* out */ sa);
assert.deepEqual(bufToUint32Array(sa), [10, 7, 0, 3, 5, 8, 1, 4, 6, 9, 2]);

/*
  Burrows-Wheeler transform
 */
var t = new Buffer('banana'),
    u = new Buffer(t.length),
    aux = new Buffer(4 * t.length);
    
// "u" receives the BWT transformed version of "t". "aux" is temporary storage.
// Returns the primary index (index of original first char in t). Will throw if 
// anything goes wrong.
var idx = divbwt(t, /* out */ u, /* tmp */ aux);
var us = u.toString(),
    result = us.slice(0, idx) + '$' + us.slice(idx);
assert.equal(result, 'annb$aa');

/* For testing */
function bufToUint32Array(buf) {
    var ret = [];
    for(var i=0; i<buf.length; i+=4) {
        ret.push(buf.readUint32LE(i));
    }
    return ret;
}

Ensure the libdivsufsort library and headers are installed as per instructions below. This addon uses whatever is installed on your system, not a vendored copy.

npm install divsufsort

brew install homebrew/science/libdivsufsort

• Requires cmake >= 2.4.2, make, C compiler.

git clone https://github.com/y-256/libdivsufsort
mkdir libdivsufsort/build
cd libdivsufsort/build
cmake -DCMAKE_BUILD_TYPE="Release" -DCMAKE_INSTALL_PREFIX="/usr/local" .. 
make && sudo make install

The largest buffer I could allocate on 64-bit OSX builds of node:

var b = new Buffer(Math.pow(2, 30) - 1);  // Works
var c = new Buffer(Math.pow(2, 30));      // Fails

• 0.10.36 - RangeError: length > kMaxLength
• 0.12.0 - RangeError: Attempt to allocate Buffer larger than maximum size: 0x3fffffff bytes

So a bit less than 1GB in both cases. This means that the largest strings you can work with will be 256MB or so.

SA construction or BWT on a 256MB string blocks for about 2 secs on my laptop, so if you're not writing a console program you probably want to do it in an external process.

• Consider whether it is possible to do a 64-bit version.
• Currently, no effort is made to handle Unicode or UTF8-encoded strings. Part of the problem is that the lib uses some auxiliary space which is quadratic in the size of the alphabet.
• It would be possible to make the binding more "JavaScript-ey" by removing the requirement for pre-allocated buffers.