Awesome

node-bitmap-ewah

A set of NodeJS bindings for a compressed bitmap data structure.

Inspired by node-ewah (installation fails due to deprecated use of node-waf).

Installation

# We use node-gyp to build our binaries
npm install -g node-gyp

# Install node-bitmap-ewah
npm install node-bitmap-ewah

Usage

var Bitmap = require('node-bitmap-ewah');

var bitmap = Bitmap.createObject();

API

• <a href="#ctor"><code><b>createObject()</b></code></a>
• <a href="#push"><code><b>push()</b></code></a>
• <a href="#set"><code><b>set()</b></code></a>
• <a href="#unset"><code><b>unset()</b></code></a>
• <a href="#str"><code><b>toString()</b></code></a>
• <a href="#len"><code><b>length()</b></code></a>
• <a href="#ones"><code><b>numberOfOnes()</b></code></a>
• <a href="#map"><code><b>map()</b></code></a>
• <a href="#or"><code><b>or()</b></code></a>
• <a href="#and"><code><b>and()</b></code></a>
• <a href="#not"><code><b>not()</b></code></a>
• <a href="#write"><code><b>write()</b></code></a>
• <a href="#read"><code><b>read()</b></code></a>

<a name="ctor"></a>

createObject()

<code>createObject()</code> is the main entry point for creating a new compressed bitmap instance.

<a name="push"></a>

push(bit_pos)

<code>push()</code> appends a set bit (1) to the bitmap in position bit_pos. All bits between the last set bit and bit_pos are appended as unset bits (0).

<a name="set"></a>

set(bit_pos)

<code>set()</code> sets the bit in position bit_pos, provided it is already appended. Has no effect if bit is already set.

<a name="unset"></a>

unset(bit_pos)

<code>unset()</code> unsets the bit in position bit_pos, provided it is already appended. Has no effect if bit is already unset.

<a name="str"></a>

toString(delimeter)

<code>toString()</code> returns a string containing the positions of set bits, separated with the delimeter character.

<a name="len"></a>

length()

<code>length()</code> returns the uncopressed bitmap's size in bits.

<a name="ones"></a>

numberOfOnes()

<code>numberOfOnes()</code> returns the number of set bits in the bitmap.

<a name="map"></a>

map(callback)

<code>map()</code> returns an array with the results of calling the callback function on each bit positiion that is set.

<a name="or"></a>

or(bitmap)

<code>or()</code> applies the logical OR between two bitmaps.

<a name="and"></a>

and(bitmap)

<code>and()</code> applies the logical AND between two bitmaps.

<a name="not"></a>

not()

<code>not()</code> applies the logical NOT to a bitmap.

<a name="write"></a>

write()

<code>write()</code> can be used to store a bitmap to persistent storage. It returns a three element array which contains the bitmap's size in bits (1st position), the size (in words) of the underlying C++ STL vector (2nd positions) and a NodeJS [Buffer] (https://nodejs.org/api/buffer.html#buffer_buffer) class object representing the bitmap's content (3rd position).

<a name="read"></a>

read([sizeInBits, bufferSisze, Buffer])

<code>read()</code> can be used to retriece a bitmap stored in persistent storage. It takes as argument an array of the same format as returned from the <a href="#write"><code><b>write()</b></code></a> function