1 | /**************************************************************************
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2 | *
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3 | * Weights.cpp -- Dealing with document weights
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4 | * Copyright (C) 1999 Rodger McNab
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5 | *
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6 | * This program is free software; you can redistribute it and/or modify
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7 | * it under the terms of the GNU General Public License as published by
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8 | * the Free Software Foundation; either version 2 of the License, or
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9 | * (at your option) any later version.
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10 | *
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11 | * This program is distributed in the hope that it will be useful,
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12 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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13 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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14 | * GNU General Public License for more details.
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15 | *
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16 | * You should have received a copy of the GNU General Public License
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17 | * along with this program; if not, write to the Free Software
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18 | * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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19 | *
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20 | **************************************************************************/
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21 |
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22 | #include "UCArray.h"
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23 | #include "Weights.h"
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24 | #include "sysfuncs.h"
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25 |
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26 | #define MAXBITS (sizeof(unsigned long) * 8)
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27 |
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28 |
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29 | ApproxWeightsData::ApproxWeightsData () {
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30 | weightBuf = NULL;
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31 | table = NULL;
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32 | Free();
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33 | }
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34 |
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35 | ApproxWeightsData::~ApproxWeightsData () {
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36 | Free ();
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37 | }
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38 |
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39 | void ApproxWeightsData::Free () {
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40 | bits = 0;
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41 | mask = 0;
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42 | L = 0.0;
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43 | B = 0.0;
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44 | numLevelDocs = 0;
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45 | if (weightBuf != NULL) {
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46 | delete [] weightBuf;
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47 | weightBuf = NULL;
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48 | }
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49 | if (table != NULL) {
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50 | delete [] table;
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51 | table = NULL;
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52 | }
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53 | }
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54 |
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55 | bool ApproxWeightsData::Read (FILE *approxWeightsFile, unsigned long diskPtr,
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56 | unsigned long _numLevelDocs) {
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57 | Free ();
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58 |
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59 | // go to the appropriate place in the weights file
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60 | fseek (approxWeightsFile, diskPtr, SEEK_SET);
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61 |
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62 | // read in approx weights parameters
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63 | ReadUC (approxWeightsFile, bits);
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64 | ReadD (approxWeightsFile, L);
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65 | ReadD (approxWeightsFile, B);
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66 |
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67 | mask = (bits == 32) ? 0xffffffff : (1 << bits) - 1;
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68 | numLevelDocs = _numLevelDocs;
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69 |
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70 | // allocate buffer for the weights
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71 | unsigned long arrSize = (bits*numLevelDocs+sizeof(unsigned long)-1) / 32;
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72 | weightBuf = new unsigned long[arrSize];
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73 |
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74 | // read in the weights
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75 | unsigned long i;
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76 | for (i=0; i<arrSize; ++i) {
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77 | ReadUL (approxWeightsFile, weightBuf[i]);
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78 | }
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79 |
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80 | // create precomputed table of values if it will be small enough
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81 | // (if not small enough table == NULL
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82 | if (bits <= 12) {
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83 | unsigned long i, tableSize = (1 << bits);
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84 | table = new float[tableSize];
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85 | table[0] = L;
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86 | for (i = 1; i < tableSize; ++i)
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87 | table[i] = table[i - 1] * B;
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88 | }
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89 |
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90 | return true;
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91 | }
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92 |
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93 | float ApproxWeightsData::GetLowerApproxDocWeight (unsigned long levelDocNum) {
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94 | // sanity check
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95 | if (bits == 0 || weightBuf == NULL) return 1.0;
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96 |
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97 | register unsigned long c, pos;
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98 | register unsigned long *dw;
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99 |
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100 | // get the compressed version of the weight
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101 | pos = levelDocNum * bits;
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102 | dw = &weightBuf[pos / MAXBITS];
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103 | pos &= (MAXBITS - 1);
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104 | c = *dw >> pos;
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105 | if (pos + bits > MAXBITS)
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106 | c |= *(dw + 1) << (MAXBITS - pos);
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107 | c &= mask;
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108 |
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109 | // decompress the weight
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110 | if (table != NULL) return table[c];
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111 | return (L * pow (B, (double) c));
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112 | }
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113 |
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114 |
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115 |
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116 | float GetExactDocWeight (FILE *exactWeightsFile, unsigned long diskPtr,
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117 | unsigned long levelDocNum) {
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118 | // go to the appropriate place in the weights file
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119 | fseek (exactWeightsFile, diskPtr+sizeof(float)*levelDocNum, SEEK_SET);
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120 |
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121 | // read in the exact weight
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122 | float weight;
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123 | ReadF (exactWeightsFile, weight);
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124 |
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125 | return weight;
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126 | }
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