HammingWordDistance.cpp

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/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * Written (W) 2007-2009 Christian Gehl
 * Written (W) 1999-2009 Soeren Sonnenburg
 * Copyright (C) 1999-2009 Fraunhofer Institute FIRST and Max-Planck-Society
 */

#include "lib/common.h"
#include "distance/HammingWordDistance.h"
#include "features/Features.h"
#include "features/StringFeatures.h"
#include "lib/io.h"

using namespace shogun;

CHammingWordDistance::CHammingWordDistance(bool sign)
: CStringDistance<uint16_t>(), use_sign(sign)
{
    SG_DEBUG( "CHammingWordDistance with sign: %d created\n", (sign) ? 1 : 0);
    dictionary_size= 1<<(sizeof(uint16_t)*8);
    dictionary_weights = new float64_t[dictionary_size];
    SG_DEBUG( "using dictionary of %d bytes\n", dictionary_size);
}

CHammingWordDistance::CHammingWordDistance(
    CStringFeatures<uint16_t>* l, CStringFeatures<uint16_t>* r, bool sign)
: CStringDistance<uint16_t>(), use_sign(sign)
{
    SG_DEBUG( "CHammingWordDistance with sign: %d created\n", (sign) ? 1 : 0);
    dictionary_size= 1<<(sizeof(uint16_t)*8);
    dictionary_weights = new float64_t[dictionary_size];
    SG_DEBUG( "using dictionary of %d bytes\n", dictionary_size);

    init(l, r);
}

CHammingWordDistance::~CHammingWordDistance()
{
    cleanup();

    delete[] dictionary_weights;
}
  
bool CHammingWordDistance::init(CFeatures* l, CFeatures* r)
{
    bool result=CStringDistance<uint16_t>::init(l,r);
    return result;
}

void CHammingWordDistance::cleanup()
{
}

float64_t CHammingWordDistance::compute(int32_t idx_a, int32_t idx_b)
{
    int32_t alen, blen;
    bool free_avec, free_bvec;

    uint16_t* avec=((CStringFeatures<uint16_t>*) lhs)->
        get_feature_vector(idx_a, alen, free_avec);
    uint16_t* bvec=((CStringFeatures<uint16_t>*) rhs)->
        get_feature_vector(idx_b, blen, free_bvec);

    int32_t result=0;

    int32_t left_idx=0;
    int32_t right_idx=0;

    if (use_sign)
    {
        // hamming of: if words appear in both vectors 
        while (left_idx < alen && right_idx < blen)
        {
            uint16_t sym=avec[left_idx];
            if (avec[left_idx]==bvec[right_idx])
            {
                while (left_idx< alen && avec[left_idx]==sym)
                    left_idx++;

                while (right_idx< blen && bvec[right_idx]==sym)
                    right_idx++;
            }
            else if (avec[left_idx]<bvec[right_idx])
            {
                result++;

                while (left_idx< alen && avec[left_idx]==sym)
                    left_idx++;
            }
            else
            {
                sym=bvec[right_idx];
                result++;

                while (right_idx< blen && bvec[right_idx]==sym)
                    right_idx++;
            }
        }
    }
    else
    {
        //hamming of: if words appear in both vectors _the same number_ of times
        while (left_idx < alen && right_idx < blen)
        {
            uint16_t sym=avec[left_idx];
            if (avec[left_idx]==bvec[right_idx])
            {
                int32_t old_left_idx=left_idx;
                int32_t old_right_idx=right_idx;

                while (left_idx< alen && avec[left_idx]==sym)
                    left_idx++;

                while (right_idx< blen && bvec[right_idx]==sym)
                    right_idx++;

                if ((left_idx-old_left_idx)!=(right_idx-old_right_idx))
                    result++;
            }
            else if (avec[left_idx]<bvec[right_idx])
            {
                result++;

                while (left_idx< alen && avec[left_idx]==sym)
                    left_idx++;
            }
            else
            {
                sym=bvec[right_idx];
                result++;

                while (right_idx< blen && bvec[right_idx]==sym)
                    right_idx++;
            }
        }
    }

    while (left_idx < alen)
    {
        uint16_t sym=avec[left_idx];
        result++;

        while (left_idx< alen && avec[left_idx]==sym)
            left_idx++;
    }

    while (right_idx < blen)
    {
        uint16_t sym=bvec[right_idx];
        result++;

        while (right_idx< blen && bvec[right_idx]==sym)
            right_idx++;
    }

    ((CStringFeatures<uint16_t>*) lhs)->
        free_feature_vector(avec, idx_a, free_avec);
    ((CStringFeatures<uint16_t>*) rhs)->
        free_feature_vector(bvec, idx_b, free_bvec);

    return result;
}