1 | /* -*- c++ -*- |
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2 | |
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3 | Template Radix sort implementation |
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4 | |
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5 | This file is part of the dpp library of C++ template classes |
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6 | |
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7 | doc: http://diaxen.ssji.net/dpp/index.html |
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8 | repo: https://www.ssji.net/svn/projets/trunk/libdpp |
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9 | |
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10 | This program is free software: you can redistribute it and/or |
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11 | modify it under the terms of the GNU Lesser General Public License |
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12 | as published by the Free Software Foundation, either version 3 of |
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13 | the License, or (at your option) any later version. |
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14 | |
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15 | This program is distributed in the hope that it will be useful, but |
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16 | WITHOUT ANY WARRANTY; without even the implied warranty of |
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17 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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18 | Lesser General Public License for more details. |
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19 | |
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20 | You should have received a copy of the GNU Lesser General Public |
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21 | License along with this program. If not, see |
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22 | <http://www.gnu.org/licenses/>. |
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23 | |
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24 | (c) 2012 Alexandre Becoulet <alexandre.becoulet@free.fr> |
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25 | |
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26 | */ |
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27 | |
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28 | #ifndef DPP_RADIX_SORT_HH_ |
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29 | #define DPP_RADIX_SORT_HH_ |
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30 | |
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31 | #include <algorithm> |
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32 | #include <cassert> |
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33 | |
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34 | #include <stdint.h> |
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35 | |
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36 | /** @file @module{Radix sort} */ |
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37 | |
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38 | namespace dpp { |
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39 | |
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40 | /** @This class may be specialized to describe how radix are |
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41 | extracted from values for a given type. Specializations are |
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42 | provided for integer and floating-point types. */ |
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43 | template <typename X, size_t bits> |
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44 | struct radix_sort_type |
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45 | { |
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46 | static unsigned int extract(const X x, size_t pos) |
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47 | { |
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48 | X::_requires_8bits_radix_width_for_custom_types(); |
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49 | } |
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50 | }; |
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51 | |
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52 | /** @This provides a generic byte-slicing radix extraction function. */ |
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53 | template <typename X> |
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54 | struct radix_sort_type<const X &, 8> |
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55 | { |
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56 | static unsigned int extract(const X x, size_t pos) |
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57 | { |
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58 | const uint8_t *d = (const uint8_t *)&x; |
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59 | return d[pos]; |
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60 | } |
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61 | }; |
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62 | |
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63 | /** @internal */ |
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64 | #define _DPP_RADIX_SORT_INT(type) \ |
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65 | /** @This class provides a radix extaction function for @tt{type} integers */ \ |
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66 | template <size_t bits> \ |
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67 | struct radix_sort_type<type, bits> \ |
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68 | { \ |
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69 | static const size_t _bsize = 1 << bits; \ |
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70 | static const size_t _passes = sizeof(type) * 8 / bits + (bits % 8 != 0); \ |
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71 | \ |
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72 | static unsigned int extract(type x, size_t pos) \ |
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73 | { \ |
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74 | return (x >> (bits * pos)) & ((1 << bits) - 1); \ |
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75 | } \ |
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76 | } |
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77 | |
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78 | _DPP_RADIX_SORT_INT(signed char); |
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79 | _DPP_RADIX_SORT_INT(unsigned char); |
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80 | _DPP_RADIX_SORT_INT(signed short); |
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81 | _DPP_RADIX_SORT_INT(unsigned short); |
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82 | _DPP_RADIX_SORT_INT(signed int); |
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83 | _DPP_RADIX_SORT_INT(unsigned int); |
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84 | _DPP_RADIX_SORT_INT(signed long); |
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85 | _DPP_RADIX_SORT_INT(unsigned long); |
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86 | _DPP_RADIX_SORT_INT(signed long long); |
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87 | _DPP_RADIX_SORT_INT(unsigned long long); |
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88 | |
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89 | /** @internal */ |
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90 | #define _DPP_RADIX_SORT_FLOAT(type) \ |
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91 | /** @This class provides a radix extaction function for @tt{type} floating-point values */ \ |
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92 | template <size_t bits> \ |
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93 | struct radix_sort_type<type, bits> \ |
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94 | { \ |
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95 | static const size_t _bsize = 1 << bits; \ |
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96 | static const size_t _passes = sizeof(type) * 8 / bits + (bits % 8 != 0); \ |
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97 | \ |
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98 | static unsigned int extract(type x, size_t pos) \ |
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99 | { \ |
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100 | switch (sizeof(type)) \ |
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101 | { \ |
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102 | case 4: { \ |
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103 | int32_t v = *(int32_t*)&x; \ |
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104 | return ((((v >> 31) | (1 << 31)) ^ v) >> (bits * pos)) & ((1 << bits) - 1); \ |
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105 | } \ |
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106 | case 8: { \ |
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107 | int64_t v = *(int64_t*)&x; \ |
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108 | return ((((v >> 63) | (1ULL << 63)) ^ v) >> (bits * pos)) & ((1 << bits) - 1); \ |
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109 | } \ |
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110 | default: \ |
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111 | std::abort(); \ |
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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 | _DPP_RADIX_SORT_FLOAT(float); |
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117 | _DPP_RADIX_SORT_FLOAT(double); |
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118 | |
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119 | /** @internal */ |
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120 | template <typename X, size_t bits> |
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121 | struct _radix_sort |
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122 | { |
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123 | static const size_t _bsize = 1 << bits; |
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124 | static const size_t _passes = sizeof(X) * 8 / bits + (bits % 8 != 0); \ |
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125 | |
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126 | /** @This performs actual sorting */ |
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127 | static void sort(X *in, X *next_in, X *out, size_t len) |
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128 | { |
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129 | size_t hist[_passes][_bsize]; |
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130 | |
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131 | // zero histograms |
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132 | for (size_t j = 0; j < _passes; j++) |
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133 | for (size_t i = 0; i < _bsize; i++) |
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134 | hist[j][i] = 0; |
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135 | |
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136 | // compute histograms |
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137 | for (size_t i = 0; i < len; i++) |
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138 | for (size_t j = 0; j < _passes; j++) |
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139 | hist[j][radix_sort_type<X, bits>::extract(in[i], j)]++; |
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140 | |
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141 | // multiple passes stable radix-sort |
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142 | for (size_t j = 0; j < _passes; j++) |
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143 | { |
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144 | uintptr_t offset[_bsize], o; |
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145 | |
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146 | // compute offsets |
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147 | o = offset[0] = 0; |
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148 | for (size_t i = 1; i < _bsize; i++) |
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149 | o = offset[i] = o + hist[j][i - 1]; |
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150 | |
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151 | // reorder array |
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152 | for (size_t i = 0; i < len; i++) |
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153 | { |
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154 | size_t x = radix_sort_type<X, bits>::extract(in[i], j); |
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155 | out[offset[x]++] = in[i]; |
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156 | } |
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157 | |
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158 | // swap input/output arrays for next pass |
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159 | in = next_in; |
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160 | std::swap(in, out); |
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161 | next_in = in; |
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162 | } |
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163 | } |
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164 | |
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165 | /** @This performs sorting and final array copy when number of passes are odd |
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166 | and sorting result must be stored back in original array. */ |
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167 | static void sort_in(X *in, size_t len) |
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168 | { |
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169 | X tmp[len]; |
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170 | |
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171 | sort(in, in, tmp, len); |
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172 | |
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173 | if (_passes % 2) |
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174 | for (size_t i = 0; i < len; i++) |
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175 | in[i] = tmp[i]; |
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176 | } |
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177 | |
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178 | /** @This performs input array copy to temporary storage when |
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179 | number of passes are odd and sorting. */ |
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180 | static void sort_out(const X *in, X *out, size_t len) |
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181 | { |
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182 | if (_passes % 2) |
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183 | { |
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184 | X tmp[len]; |
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185 | |
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186 | for (size_t i = 0; i < len; i++) |
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187 | tmp[i] = in[i]; |
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188 | sort(tmp, tmp, out, len); |
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189 | } |
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190 | else if (_passes > 1) |
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191 | { |
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192 | X tmp[len]; |
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193 | sort((X*)in, out, tmp, len); |
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194 | } |
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195 | else |
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196 | { |
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197 | sort((X*)in, 0, out, len); |
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198 | } |
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199 | } |
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200 | }; |
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201 | |
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202 | /** @This function performs radix-sort on container iterators. Radix |
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203 | width is 8 bits. */ |
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204 | template <typename iterator> |
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205 | void radix_sort(const iterator &begin, const iterator &end) |
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206 | { |
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207 | typedef typename iterator::value_type type; |
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208 | size_t len = end - begin; |
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209 | |
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210 | _radix_sort<type, 8>::sort_in(&*begin, len); |
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211 | } |
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212 | |
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213 | /** @This function performs radix-sort on container |
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214 | iterators. Specified radix bit width is used. */ |
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215 | template <typename iterator, size_t bits> |
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216 | void radix_sort(const iterator &begin, const iterator &end) |
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217 | { |
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218 | typedef typename iterator::value_type type; |
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219 | size_t len = end - begin; |
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220 | |
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221 | _radix_sort<type, bits>::sort_in(&*begin, len); |
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222 | } |
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223 | |
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224 | /** @This function performs radix-sort on array. Radix |
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225 | width is 8 bits. */ |
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226 | template <typename X> |
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227 | void radix_sort(X *begin, X *end) |
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228 | { |
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229 | typedef X type; |
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230 | size_t len = end - begin; |
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231 | |
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232 | _radix_sort<type, 8>::sort_in(begin, len); |
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233 | } |
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234 | |
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235 | /** @This function performs radix-sort on array. |
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236 | Specified radix bit width is used. */ |
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237 | template <typename X, size_t bits> |
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238 | void radix_sort(X *begin, X *end) |
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239 | { |
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240 | typedef X type; |
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241 | size_t len = end - begin; |
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242 | |
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243 | _radix_sort<type, bits>::sort_in(begin, len); |
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244 | } |
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245 | |
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246 | /** @This function performs radix-sort on array. Radix |
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247 | width is 8 bits. */ |
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248 | template <typename X> |
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249 | void radix_sort(const X *begin, const X *end, X *out) |
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250 | { |
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251 | typedef X type; |
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252 | size_t len = end - begin; |
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253 | |
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254 | _radix_sort<type, 8>::sort_out(begin, out, len); |
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255 | } |
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256 | |
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257 | /** @This function performs radix-sort on array. |
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258 | Specified radix bit width is used. */ |
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259 | template <typename X, size_t bits> |
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260 | void radix_sort(const X *begin, const X *end, X *out) |
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261 | { |
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262 | typedef X type; |
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263 | size_t len = end - begin; |
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264 | |
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265 | _radix_sort<type, bits>::sort_out(begin, out, len); |
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266 | } |
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267 | |
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268 | } |
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269 | |
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270 | #endif |
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271 | |
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