Javascript implementation of Murmurhash3 to give the same result as Murmurhash3.cpp used by transform available in Python's sklearn
<p>(I am VERY sorry I am not allowed to add many URLs to help me better explain my problems in this post because I am new on StackOverflow and my StackOverflow account has very low privilege).</p>

<p><strong>Summary</strong> </p>

<p>Can anyone please guide me on how to modify <code>murmurhash3.js</code> (below) so that it produces the same hash as <code>MurmurHash3.cpp</code> (below) does? I provide a simple python code "simple_python_wrapper.py" for MurmurHash3.cpp based on what I need. The simple_python_wrapper.py should work on your computer if you have sklearn installed.</p>

<p>I have heavily used <code>Murmurhash3.cpp</code> (shown below) while using <code>transform</code> from sklearn (a Python Machine Learning Library): <code>from sklearn.feature_extraction._hashing import transform</code> in one of my machine learning projects. <code>transform</code> uses <code>Murmurhash3.cpp</code> deep down in sklearn's  implementation/import tree.</p>

<p><strong>More details</strong></p>

<p><strong><em>hash % (2^18) {that is "hash modulus 2^18"} based on MurmurHash3.cpp</em></strong></p>

<pre><code>"hello" gives 260679
"there" gives 45525
</code></pre>

<p><strong><em>hash % (2^18) {that is "hash modulus 2^18"} based on murmurhash3.js</em></strong></p>

<pre><code>"hello" gives -58999
"there" gives 65775
</code></pre>

<p><strong><em>murmurhash3.js</em></strong></p>

<pre><code>/*
 *  The MurmurHash3 algorithm was created by Austin Appleby.  This JavaScript port was authored
 *  by whitequark (based on Java port by Yonik Seeley) and is placed into the public domain.
 *  The author hereby disclaims copyright to this source code.
 *
 *  This produces exactly the same hash values as the final C++ version of MurmurHash3 and
 *  is thus suitable for producing the same hash values across platforms.
 *
 *  There are two versions of this hash implementation. First interprets the string as a
 *  sequence of bytes, ignoring most significant byte of each codepoint. The second one
 *  interprets the string as a UTF-16 codepoint sequence, and appends each 16-bit codepoint
 *  to the hash independently. The latter mode was not written to be compatible with
 *  any other implementation, but it should offer better performance for JavaScript-only
 *  applications.
 *
 *  See http://github.com/whitequark/murmurhash3-js for future updates to this file.
 */

var MurmurHash3 = {
    mul32: function(m, n) {
        var nlo = n &amp; 0xffff;
        var nhi = n - nlo;
        return ((nhi * m | 0) + (nlo * m | 0)) | 0;
    },

    hashBytes: function(data, len, seed) {
        var c1 = 0xcc9e2d51, c2 = 0x1b873593;

        var h1 = seed;
        var roundedEnd = len &amp; ~0x3;

        for (var i = 0; i &lt; roundedEnd; i += 4) {
            var k1 = (data.charCodeAt(i)     &amp; 0xff)        |
                ((data.charCodeAt(i + 1) &amp; 0xff) &lt;&lt; 8)  |
                ((data.charCodeAt(i + 2) &amp; 0xff) &lt;&lt; 16) |
                ((data.charCodeAt(i + 3) &amp; 0xff) &lt;&lt; 24);

            k1 = this.mul32(k1, c1);
            k1 = ((k1 &amp; 0x1ffff) &lt;&lt; 15) | (k1 &gt;&gt;&gt; 17);  // ROTL32(k1,15);
            k1 = this.mul32(k1, c2);

            h1 ^= k1;
            h1 = ((h1 &amp; 0x7ffff) &lt;&lt; 13) | (h1 &gt;&gt;&gt; 19);  // ROTL32(h1,13);
            h1 = (h1 * 5 + 0xe6546b64) | 0;
        }

        k1 = 0;

        switch(len % 4) {
            case 3:
                k1 = (data.charCodeAt(roundedEnd + 2) &amp; 0xff) &lt;&lt; 16;
                // fallthrough
            case 2:
                k1 |= (data.charCodeAt(roundedEnd + 1) &amp; 0xff) &lt;&lt; 8;
                // fallthrough
            case 1:
                k1 |= (data.charCodeAt(roundedEnd) &amp; 0xff);
                k1 = this.mul32(k1, c1);
                k1 = ((k1 &amp; 0x1ffff) &lt;&lt; 15) | (k1 &gt;&gt;&gt; 17);  // ROTL32(k1,15);
                k1 = this.mul32(k1, c2);
                h1 ^= k1;
        }

        // finalization
        h1 ^= len;

        // fmix(h1);
        h1 ^= h1 &gt;&gt;&gt; 16;
        h1  = this.mul32(h1, 0x85ebca6b);
        h1 ^= h1 &gt;&gt;&gt; 13;
        h1  = this.mul32(h1, 0xc2b2ae35);
        h1 ^= h1 &gt;&gt;&gt; 16;

        return h1;
    },

    hashString: function(data, len, seed) {
        var c1 = 0xcc9e2d51, c2 = 0x1b873593;

        var h1 = seed;
        var roundedEnd = len &amp; ~0x1;

        for (var i = 0; i &lt; roundedEnd; i += 2) {
            var k1 = data.charCodeAt(i) | (data.charCodeAt(i + 1) &lt;&lt; 16);

            k1 = this.mul32(k1, c1);
            k1 = ((k1 &amp; 0x1ffff) &lt;&lt; 15) | (k1 &gt;&gt;&gt; 17);  // ROTL32(k1,15);
            k1 = this.mul32(k1, c2);

            h1 ^= k1;
            h1 = ((h1 &amp; 0x7ffff) &lt;&lt; 13) | (h1 &gt;&gt;&gt; 19);  // ROTL32(h1,13);
            h1 = (h1 * 5 + 0xe6546b64) | 0;
        }

        if((len % 2) == 1) {
            k1 = data.charCodeAt(roundedEnd);
            k1 = this.mul32(k1, c1);
            k1 = ((k1 &amp; 0x1ffff) &lt;&lt; 15) | (k1 &gt;&gt;&gt; 17);  // ROTL32(k1,15);
            k1 = this.mul32(k1, c2);
            h1 ^= k1;
        }

        // finalization
        h1 ^= (len &lt;&lt; 1);

        // fmix(h1);
        h1 ^= h1 &gt;&gt;&gt; 16;
        h1  = this.mul32(h1, 0x85ebca6b);
        h1 ^= h1 &gt;&gt;&gt; 13;
        h1  = this.mul32(h1, 0xc2b2ae35);
        h1 ^= h1 &gt;&gt;&gt; 16;

        return h1;
    }
};

if(typeof module !== "undefined" &amp;&amp; typeof module.exports !== "undefined") {
    module.exports = MurmurHash3;
}
</code></pre>

<p><strong><em>Here is the HTML code + Javascript I am using to test the javascript</em></strong></p>

<p><a href="https://jsbin.com/gicomikike/edit?html,js,output" rel="nofollow">https://jsbin.com/gicomikike/edit?html,js,output</a> </p>

<pre><code>&lt;html&gt;
&lt;head&gt;

&lt;script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.0/jquery.min.js"&gt;&lt;/script&gt;
&lt;script src="murmurhash3.js"&gt;&lt;/script&gt;

&lt;script&gt;

function call_murmurhash3_32_gc () {
    var key = $('textarea#textarea1').val();
    var seed = 0;
    var hash = MurmurHash3.hashString (key, key.length, seed);
    $('div#div1').text(hash);
    }
&lt;/script&gt;

&lt;/head&gt;
&lt;body&gt;
Body

&lt;form&gt;

    &lt;textarea rows="4" cols="50" id=textarea1&gt;&lt;/textarea&gt;

    &lt;br&gt;
    &lt;input type="button" value="Hash" onclick="call_murmurhash3_32_gc()"/&gt;

&lt;/form&gt;


&lt;div id=div1&gt;

&lt;/div&gt;

&lt;/body&gt;
&lt;/html&gt;
</code></pre>

<p><strong><em>simple_python_wrapper.py</em></strong></p>

<p>This makes use of MurmurHash3.cpp in sklearn's import tree.</p>

<pre><code>from sklearn.feature_extraction._hashing import transform 
import numpy as np

def getHashIndex (words):

    raw_X = words
    n_features = 262144 # 2 ** 18
    dtype = np.float32 #np.float64

    #transform(raw_X, Py_ssize_t n_features, dtype)
    indices_a, indptr, values = transform (raw_X, n_features, dtype)

    return indices_a 


words = [[("hello", 1), ("there", 1)]] 

print getHashIndex (words)
</code></pre>

<p>Output</p>

<pre><code>[260679  45525]
</code></pre>

<p><strong><em>MurmurHash3.cpp</em></strong></p>

<pre><code>I copied this code is available here 
https://github.com/karanlyons/murmurHash3.js/blob/master/murmurHash3.js
//-----------------------------------------------------------------------------
// MurmurHash3 was written by Austin Appleby, and is placed in the public
// domain. The author hereby disclaims copyright to this source code.

// Note - The x86 and x64 versions do _not_ produce the same results, as the
// algorithms are optimized for their respective platforms. You can still
// compile and run any of them on any platform, but your performance with the
// non-native version will be less than optimal.

#include "MurmurHash3.h"

//-----------------------------------------------------------------------------
// Platform-specific functions and macros

// Microsoft Visual Studio

#if defined(_MSC_VER)

#define FORCE_INLINE    __forceinline

#include &lt;stdlib.h&gt;

#define ROTL32(x,y) _rotl(x,y)
#define ROTL64(x,y) _rotl64(x,y)

#define BIG_CONSTANT(x) (x)

// Other compilers

#else   // defined(_MSC_VER)

#if defined(GNUC) &amp;&amp; ((GNUC &gt; 4) || (GNUC == 4 &amp;&amp; GNUC_MINOR &gt;= 4))

/* gcc version &gt;= 4.4 4.1 = RHEL 5, 4.4 = RHEL 6.
 * Don't inline for RHEL 5 gcc which is 4.1 */
#define FORCE_INLINE attribute((always_inline))

#else

#define FORCE_INLINE

#endif


inline uint32_t rotl32 ( uint32_t x, int8_t r )
{
  return (x &lt;&lt; r) | (x &gt;&gt; (32 - r));
}

inline uint64_t rotl64 ( uint64_t x, int8_t r )
{
  return (x &lt;&lt; r) | (x &gt;&gt; (64 - r));
}

#define ROTL32(x,y) rotl32(x,y)
#define ROTL64(x,y) rotl64(x,y)

#define BIG_CONSTANT(x) (x##LLU)

#endif // !defined(_MSC_VER)

//-----------------------------------------------------------------------------
// Block read - if your platform needs to do endian-swapping or can only
// handle aligned reads, do the conversion here

FORCE_INLINE uint32_t getblock ( const uint32_t * p, int i )
{
  return p[i];
}

FORCE_INLINE uint64_t getblock ( const uint64_t * p, int i )
{
  return p[i];
}

//-----------------------------------------------------------------------------
// Finalization mix - force all bits of a hash block to avalanche

FORCE_INLINE uint32_t fmix ( uint32_t h )
{
  h ^= h &gt;&gt; 16;
  h *= 0x85ebca6b;
  h ^= h &gt;&gt; 13;
  h *= 0xc2b2ae35;
  h ^= h &gt;&gt; 16;

  return h;
}

//----------

FORCE_INLINE uint64_t fmix ( uint64_t k )
{
  k ^= k &gt;&gt; 33;
  k *= BIG_CONSTANT(0xff51afd7ed558ccd);
  k ^= k &gt;&gt; 33;
  k *= BIG_CONSTANT(0xc4ceb9fe1a85ec53);
  k ^= k &gt;&gt; 33;

  return k;
}

//-----------------------------------------------------------------------------

void MurmurHash3_x86_32 ( const void * key, int len,
                          uint32_t seed, void * out )
{
  const uint8_t * data = (const uint8_t*)key;
  const int nblocks = len / 4;

  uint32_t h1 = seed;

  uint32_t c1 = 0xcc9e2d51;
  uint32_t c2 = 0x1b873593;

  //----------
  // body

  const uint32_t * blocks = (const uint32_t *)(data + nblocks*4);

  for(int i = -nblocks; i; i++)
  {
    uint32_t k1 = getblock(blocks,i);

    k1 *= c1;
    k1 = ROTL32(k1,15);
    k1 *= c2;

    h1 ^= k1;
    h1 = ROTL32(h1,13);
    h1 = h1*5+0xe6546b64;
  }

  //----------
  // tail

  const uint8_t * tail = (const uint8_t*)(data + nblocks*4);

  uint32_t k1 = 0;

  switch(len &amp; 3)
  {
  case 3: k1 ^= tail[2] &lt;&lt; 16;
  case 2: k1 ^= tail[1] &lt;&lt; 8;
  case 1: k1 ^= tail[0];
          k1 *= c1; k1 = ROTL32(k1,15); k1 *= c2; h1 ^= k1;
  };

  //----------
  // finalization

  h1 ^= len;

  h1 = fmix(h1);

  *(uint32_t*)out = h1;
}

//-----------------------------------------------------------------------------

void MurmurHash3_x86_128 ( const void * key, const int len,
                           uint32_t seed, void * out )
{
  const uint8_t * data = (const uint8_t*)key;
  const int nblocks = len / 16;

  uint32_t h1 = seed;
  uint32_t h2 = seed;
  uint32_t h3 = seed;
  uint32_t h4 = seed;

  uint32_t c1 = 0x239b961b;
  uint32_t c2 = 0xab0e9789;
  uint32_t c3 = 0x38b34ae5;
  uint32_t c4 = 0xa1e38b93;

  //----------
  // body

  const uint32_t * blocks = (const uint32_t *)(data + nblocks*16);

  for(int i = -nblocks; i; i++)
  {
    uint32_t k1 = getblock(blocks,i*4+0);
    uint32_t k2 = getblock(blocks,i*4+1);
    uint32_t k3 = getblock(blocks,i*4+2);
    uint32_t k4 = getblock(blocks,i*4+3);

    k1 *= c1; k1  = ROTL32(k1,15); k1 *= c2; h1 ^= k1;

    h1 = ROTL32(h1,19); h1 += h2; h1 = h1*5+0x561ccd1b;

    k2 *= c2; k2  = ROTL32(k2,16); k2 *= c3; h2 ^= k2;

    h2 = ROTL32(h2,17); h2 += h3; h2 = h2*5+0x0bcaa747;

    k3 *= c3; k3  = ROTL32(k3,17); k3 *= c4; h3 ^= k3;

    h3 = ROTL32(h3,15); h3 += h4; h3 = h3*5+0x96cd1c35;

    k4 *= c4; k4  = ROTL32(k4,18); k4 *= c1; h4 ^= k4;

    h4 = ROTL32(h4,13); h4 += h1; h4 = h4*5+0x32ac3b17;
  }

  //----------
  // tail

  const uint8_t * tail = (const uint8_t*)(data + nblocks*16);

  uint32_t k1 = 0;
  uint32_t k2 = 0;
  uint32_t k3 = 0;
  uint32_t k4 = 0;

  switch(len &amp; 15)
  {
  case 15: k4 ^= tail[14] &lt;&lt; 16;
  case 14: k4 ^= tail[13] &lt;&lt; 8;
  case 13: k4 ^= tail[12] &lt;&lt; 0;
           k4 *= c4; k4  = ROTL32(k4,18); k4 *= c1; h4 ^= k4;

  case 12: k3 ^= tail[11] &lt;&lt; 24;
  case 11: k3 ^= tail[10] &lt;&lt; 16;
  case 10: k3 ^= tail[ 9] &lt;&lt; 8;
  case  9: k3 ^= tail[ 8] &lt;&lt; 0;
           k3 *= c3; k3  = ROTL32(k3,17); k3 *= c4; h3 ^= k3;

  case  8: k2 ^= tail[ 7] &lt;&lt; 24;
  case  7: k2 ^= tail[ 6] &lt;&lt; 16;
  case  6: k2 ^= tail[ 5] &lt;&lt; 8;
  case  5: k2 ^= tail[ 4] &lt;&lt; 0;
           k2 *= c2; k2  = ROTL32(k2,16); k2 *= c3; h2 ^= k2;

  case  4: k1 ^= tail[ 3] &lt;&lt; 24;
  case  3: k1 ^= tail[ 2] &lt;&lt; 16;
  case  2: k1 ^= tail[ 1] &lt;&lt; 8;
  case  1: k1 ^= tail[ 0] &lt;&lt; 0;
           k1 *= c1; k1  = ROTL32(k1,15); k1 *= c2; h1 ^= k1;
  };

  //----------
  // finalization

  h1 ^= len; h2 ^= len; h3 ^= len; h4 ^= len;

  h1 += h2; h1 += h3; h1 += h4;
  h2 += h1; h3 += h1; h4 += h1;

  h1 = fmix(h1);
  h2 = fmix(h2);
  h3 = fmix(h3);
  h4 = fmix(h4);

  h1 += h2; h1 += h3; h1 += h4;
  h2 += h1; h3 += h1; h4 += h1;

  ((uint32_t*)out)[0] = h1;
  ((uint32_t*)out)[1] = h2;
  ((uint32_t*)out)[2] = h3;
  ((uint32_t*)out)[3] = h4;
}

//-----------------------------------------------------------------------------

void MurmurHash3_x64_128 ( const void * key, const int len,
                           const uint32_t seed, void * out )
{
  const uint8_t * data = (const uint8_t*)key;
  const int nblocks = len / 16;

  uint64_t h1 = seed;
  uint64_t h2 = seed;

  uint64_t c1 = BIG_CONSTANT(0x87c37b91114253d5);
  uint64_t c2 = BIG_CONSTANT(0x4cf5ad432745937f);

  //----------
  // body

  const uint64_t * blocks = (const uint64_t *)(data);

  for(int i = 0; i &lt; nblocks; i++)
  {
    uint64_t k1 = getblock(blocks,i*2+0);
    uint64_t k2 = getblock(blocks,i*2+1);

    k1 *= c1; k1  = ROTL64(k1,31); k1 *= c2; h1 ^= k1;

    h1 = ROTL64(h1,27); h1 += h2; h1 = h1*5+0x52dce729;

    k2 *= c2; k2  = ROTL64(k2,33); k2 *= c1; h2 ^= k2;

    h2 = ROTL64(h2,31); h2 += h1; h2 = h2*5+0x38495ab5;
  }

  //----------
  // tail

  const uint8_t * tail = (const uint8_t*)(data + nblocks*16);

  uint64_t k1 = 0;
  uint64_t k2 = 0;

  switch(len &amp; 15)
  {
  case 15: k2 ^= uint64_t(tail[14]) &lt;&lt; 48;
  case 14: k2 ^= uint64_t(tail[13]) &lt;&lt; 40;
  case 13: k2 ^= uint64_t(tail[12]) &lt;&lt; 32;
  case 12: k2 ^= uint64_t(tail[11]) &lt;&lt; 24;
  case 11: k2 ^= uint64_t(tail[10]) &lt;&lt; 16;
  case 10: k2 ^= uint64_t(tail[ 9]) &lt;&lt; 8;
  case  9: k2 ^= uint64_t(tail[ 8]) &lt;&lt; 0;
           k2 *= c2; k2  = ROTL64(k2,33); k2 *= c1; h2 ^= k2;

  case  8: k1 ^= uint64_t(tail[ 7]) &lt;&lt; 56;
  case  7: k1 ^= uint64_t(tail[ 6]) &lt;&lt; 48;
  case  6: k1 ^= uint64_t(tail[ 5]) &lt;&lt; 40;
  case  5: k1 ^= uint64_t(tail[ 4]) &lt;&lt; 32;
  case  4: k1 ^= uint64_t(tail[ 3]) &lt;&lt; 24;
  case  3: k1 ^= uint64_t(tail[ 2]) &lt;&lt; 16;
  case  2: k1 ^= uint64_t(tail[ 1]) &lt;&lt; 8;
  case  1: k1 ^= uint64_t(tail[ 0]) &lt;&lt; 0;
           k1 *= c1; k1  = ROTL64(k1,31); k1 *= c2; h1 ^= k1;
  };

  //----------
  // finalization

  h1 ^= len; h2 ^= len;

  h1 += h2;
  h2 += h1;

  h1 = fmix(h1);
  h2 = fmix(h2);

  h1 += h2;
  h2 += h1;

  ((uint64_t*)out)[0] = h1;
  ((uint64_t*)out)[1] = h2;
}

//-----------------------------------------------------------------------------
</code></pre>

<p>Let me explain that a bit more. </p>

<p><code>from sklearn.feature_extraction._hashing import transform</code> 
makes use of this code <code>https://github.com/scikit-learn/scikit-learn/blob/412996f09b6756752dfd3736c306d46fca8f1aa1/sklearn/feature_extraction/_hashing.pyx</code>
which makes use of this
<code>from sklearn.utils.murmurhash cimport murmurhash3_bytes_s32</code> 
which in turn makes use of this
<code>https://github.com/scikit-learn/scikit-learn/blob/master/sklearn/utils/murmurhash.pyx</code> 
which is built on this
<a href="https://github.com/scikit-learn/scikit-learn/blob/master/sklearn/utils/src/MurmurHash3.cpp" rel="nofollow">https://github.com/scikit-learn/scikit-learn/blob/master/sklearn/utils/src/MurmurHash3.cpp</a> . <strong>So, MurmurHash3.cpp is very important. I need a Javascript version of this exact MurmurHash3.cpp such that the Javascript code and MurmurHash3.cpp would produce the same result</strong>.</p>

<p>I need this because I want to make some of my machine learning tools available online and the hashing needs to be done on the client's web browser.</p>

<p>So far, I have found a few Javascript implementations of MurmurHash3. However, murmurhash3.js <code>https://github.com/whitequark/murmurhash3-js/blob/master/murmurhash3.js</code> seems to be closest (in terms of codes structure) to the MurmurHash3.cpp used by sklearn. But I still d not get the same hash from both of them. </p>

<p>Can anyone please guide me on how to modify <code>murmurhash3.js</code> (above) so that it produces the same hash as <code>MurmurHash3.cpp</code> (above) does?</p>

<p>Based on suggestions from @ChristopherOicles, I changed my <code>Javascript</code> code (my the header off my HTML code) to use <code>hashBytes</code> instead of <code>hashString</code> as shown below. I also noticed that I needed to change the returned value of <code>hashBytes</code> to its absolute value for my purpose (so I did). These solve my problems and now I get the same hash from the Python/C++ codes and from the Javascript codes.</p>

<p><strong>Modified Javascript Function in my HTML file</strong></p>

<pre><code>&lt;script&gt;
function call_murmurhash3_32_gc () {
    var key = $('textarea#textarea1').val();
    var seed = 0;
    var hash = MurmurHash3.hashBytes (key, key.length, seed);
    $('div#div1').text(Math.abs (hash) % 262144);
    }
&lt;/script&gt;
</code></pre>

<p>My complete solution is here <a href="https://jsbin.com/qilokot/edit?html,js,output" rel="nofollow">https://jsbin.com/qilokot/edit?html,js,output</a>
.</p>

<p>Again, many thanks to <code>Christopher Oicles</code> and to everyone who tried to help me in some ways. </p>

javascript python c++ scikit-learn murmurhash