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1 // Part 2 about a "Compiler" for the Brainf*** language |
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2 //====================================================== |
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3 |
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4 object CW10b { |
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5 |
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6 // !!! Copy any function you need from file bf.scala !!! |
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7 // |
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8 // If you need any auxiliary function, feel free to |
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9 // implement it, but do not make any changes to the |
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10 // templates below. |
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11 |
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12 |
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13 def time_needed[T](n: Int, code: => T) = { |
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14 val start = System.nanoTime() |
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15 for (i <- 0 until n) code |
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16 val end = System.nanoTime() |
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17 (end - start)/(n * 1.0e9) |
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18 } |
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19 |
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20 type Mem = Map[Int, Int] |
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21 |
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22 |
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23 import io.Source |
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24 import scala.util._ |
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25 |
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26 def load_bff(name: String) : String = |
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27 Try(Source.fromFile(name)("ISO-8859-1").mkString).getOrElse("") |
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28 |
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29 def sread(mem: Mem, mp: Int) : Int = |
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30 mem.getOrElse(mp, 0) |
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31 |
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32 def write(mem: Mem, mp: Int, v: Int) : Mem = |
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33 mem.updated(mp, v) |
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34 |
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35 def jumpRight(prog: String, pc: Int, level: Int) : Int = { |
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36 if (prog.length <= pc) pc |
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37 else (prog(pc), level) match { |
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38 case (']', 0) => pc + 1 |
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39 case (']', l) => jumpRight(prog, pc + 1, l - 1) |
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40 case ('[', l) => jumpRight(prog, pc + 1, l + 1) |
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41 case (_, l) => jumpRight(prog, pc + 1, l) |
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42 } |
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43 } |
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44 |
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45 def jumpLeft(prog: String, pc: Int, level: Int) : Int = { |
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46 if (pc < 0) pc |
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47 else (prog(pc), level) match { |
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48 case ('[', 0) => pc + 1 |
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49 case ('[', l) => jumpLeft(prog, pc - 1, l - 1) |
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50 case (']', l) => jumpLeft(prog, pc - 1, l + 1) |
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51 case (_, l) => jumpLeft(prog, pc - 1, l) |
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52 } |
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53 } |
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54 |
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55 def compute(prog: String, pc: Int, mp: Int, mem: Mem) : Mem = { |
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56 if (0 <= pc && pc < prog.length) { |
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57 val (new_pc, new_mp, new_mem) = prog(pc) match { |
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58 case '>' => (pc + 1, mp + 1, mem) |
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59 case '<' => (pc + 1, mp - 1, mem) |
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60 case '+' => (pc + 1, mp, write(mem, mp, sread(mem, mp) + 1)) |
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61 case '-' => (pc + 1, mp, write(mem, mp, sread(mem, mp) - 1)) |
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62 case '.' => { print(sread(mem, mp).toChar); (pc + 1, mp, mem) } |
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63 case ',' => (pc + 1, mp, write(mem, mp, Console.in.read().toByte)) |
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64 case '[' => |
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65 if (sread(mem, mp) == 0) (jumpRight(prog, pc + 1, 0), mp, mem) else (pc + 1, mp, mem) |
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66 case ']' => |
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67 if (sread(mem, mp) != 0) (jumpLeft(prog, pc - 1, 0), mp, mem) else (pc + 1, mp, mem) |
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68 case _ => (pc + 1, mp, mem) |
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69 } |
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70 compute(prog, new_pc, new_mp, new_mem) |
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71 } |
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72 else mem |
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73 } |
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74 |
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75 def run(prog: String, m: Mem = Map()) = compute(prog, 0, 0, m) |
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76 |
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77 |
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78 // The baseline to what we can compare our "compiler" |
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79 // implemented below. It should require something like |
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80 // 60 seconds for the calculation on my laptop |
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81 // |
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82 //time_needed(1, run(load_bff("benchmark.bf"))) |
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83 |
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84 |
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85 |
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86 // DEBUGGING INFORMATION!!! |
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87 // |
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88 // Compiler, even real ones, are fiedishly difficult to get |
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89 // to prduce correct code. The point is that for example for |
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90 // the sierpinski program, they need to still generate code |
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91 // that displays such a triangle. If yes, then one usually |
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92 // can take comfort that all is well. If not, then something |
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93 // went wrong during the optimisations. |
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94 |
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95 |
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96 |
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97 // (5) Write a function jtable that precomputes the "jump |
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98 // table" for a bf-program. This function takes a bf-program |
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99 // as an argument and Returns a Map[Int, Int]. The |
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100 // purpose of this map is to record the information |
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101 // that given on the position pc is a '[' or a ']', |
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102 // then to which pc-position do we need to jump next? |
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103 // |
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104 // For example for the program |
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105 // |
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106 // "+++++[->++++++++++<]>--<+++[->>++++++++++<<]>>++<<----------[+>.>.<+<]" |
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107 // |
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108 // we obtain the map |
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109 // |
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110 // Map(69 -> 61, 5 -> 20, 60 -> 70, 27 -> 44, 43 -> 28, 19 -> 6) |
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111 // |
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112 // This states that for the '[' on position 5, we need to |
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113 // jump to position 20, which is just after the corresponding ']'. |
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114 // Similarly, for the ']' on position 19, we need to jump to |
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115 // position 6, which is just after the '[' on position 5, and so |
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116 // on. The idea is to not calculate this information each time |
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117 // we hit a bracket, but just look up this information in the |
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118 // jtable. You can use the jumpLeft and jumpRight functions |
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119 // from Part 1 for calculating the jtable. |
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120 // |
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121 // Then adapt the compute and run functions from Part 1 in order |
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122 // to take advantage of the information stored in the jtable. |
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123 // This means whenever jumpLeft and jumpRight was called previously, |
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124 // you should look up the jump address in the jtable. |
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125 |
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126 |
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127 def jtable(pg: String) : Map[Int, Int] = |
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128 (0 until pg.length).collect { pc => pg(pc) match { |
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129 case '[' => (pc -> jumpRight(pg, pc + 1, 0)) |
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130 case ']' => (pc -> jumpLeft(pg, pc - 1, 0)) |
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131 }}.toMap |
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132 |
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133 |
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134 // testcase |
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135 // jtable("""+++++[->++++++++++<]>--<+++[->>++++++++++<<]>>++<<----------[+>.>.<+<]""") |
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136 // => Map(69 -> 61, 5 -> 20, 60 -> 70, 27 -> 44, 43 -> 28, 19 -> 6) |
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137 |
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138 |
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139 def compute2(pg: String, tb: Map[Int, Int], pc: Int, mp: Int, mem: Mem) : Mem = { |
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140 if (0 <= pc && pc < pg.length) { |
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141 val (new_pc, new_mp, new_mem) = pg(pc) match { |
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142 case '>' => (pc + 1, mp + 1, mem) |
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143 case '<' => (pc + 1, mp - 1, mem) |
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144 case '+' => (pc + 1, mp, write(mem, mp, sread(mem, mp) + 1)) |
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145 case '-' => (pc + 1, mp, write(mem, mp, sread(mem, mp) - 1)) |
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146 case '.' => { print(sread(mem, mp).toChar); (pc + 1, mp, mem) } |
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147 case ',' => (pc + 1, mp, write(mem, mp, Console.in.read().toByte)) |
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148 case '[' => |
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149 if (sread(mem, mp) == 0) (tb(pc), mp, mem) else (pc + 1, mp, mem) |
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150 case ']' => |
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151 if (sread(mem, mp) != 0) (tb(pc), mp, mem) else (pc + 1, mp, mem) |
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152 case _ => (pc + 1, mp, mem) |
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153 } |
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154 compute2(pg, tb, new_pc, new_mp, new_mem) |
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155 } |
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156 else mem |
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157 } |
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158 |
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159 |
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160 def run2(pg: String, m: Mem = Map()) = |
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161 compute2(pg, jtable(pg), 0, 0, m) |
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162 |
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163 //time_needed(1, run2(load_bff("benchmark.bf"))) |
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164 |
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165 |
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166 |
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167 // (6) Write a function optimise which deletes "dead code" (everything |
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168 // that is not a bf-command) and also replaces substrings of the form |
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169 // [-] by a new command 0. The idea is that the loop [-] just resets the |
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170 // memory at the current location to 0. In the compute3 and run3 functions |
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171 // below you implement this command by writing the number 0 to mem(mp), |
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172 // that is write(mem, mp, 0). |
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173 // |
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174 // The easiest way to modify a string in this way is to use the regular |
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175 // expression """[^<>+-.,\[\]]""", which recognises everything that is |
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176 // not a bf-command and replace it by the empty string. Similarly the |
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177 // regular expression """\[-\]""" finds all occurences of [-] and |
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178 // by using the Scala method .replaceAll you can repplace it with the |
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179 // string "0" standing for the new bf-command. |
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180 |
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181 def optimise(s: String) : String = |
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182 s.replaceAll("""[^<>+-.,\[\]]""","").replaceAll("""\[-\]""", "0") |
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183 |
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184 |
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185 def compute3(pg: String, tb: Map[Int, Int], pc: Int, mp: Int, mem: Mem) : Mem = { |
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186 if (0 <= pc && pc < pg.length) { |
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187 val (new_pc, new_mp, new_mem) = pg(pc) match { |
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188 case '0' => (pc + 1, mp, write(mem, mp, 0)) |
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189 case '>' => (pc + 1, mp + 1, mem) |
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190 case '<' => (pc + 1, mp - 1, mem) |
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191 case '+' => (pc + 1, mp, write(mem, mp, sread(mem, mp) + 1)) |
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192 case '-' => (pc + 1, mp, write(mem, mp, sread(mem, mp) - 1)) |
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193 case '.' => { print(sread(mem, mp).toChar); (pc + 1, mp, mem) } |
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194 case ',' => (pc + 1, mp, write(mem, mp, Console.in.read().toByte)) |
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195 case '[' => |
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196 if (sread(mem, mp) == 0) (tb(pc), mp, mem) else (pc + 1, mp, mem) |
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197 case ']' => |
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198 if (sread(mem, mp) != 0) (tb(pc), mp, mem) else (pc + 1, mp, mem) |
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199 case _ => (pc + 1, mp, mem) |
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200 } |
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201 compute3(pg, tb, new_pc, new_mp, new_mem) |
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202 } |
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203 else mem |
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204 } |
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205 |
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206 def run3(pg: String, m: Mem = Map()) = { |
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207 val pg_opt = optimise(pg) |
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208 compute3(pg_opt, jtable(pg_opt), 0, 0, m) |
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209 } |
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210 |
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211 |
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212 // testcases |
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213 |
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214 //optimise(load_bff("benchmark.bf")) // should have inserted 0's |
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215 //optimise(load_bff("mandelbrot.bf")).length // => 11203 |
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216 |
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217 //time_needed(1, run3(load_bff("benchmark.bf"))) |
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218 |
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219 |
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220 |
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221 // (7) Write a function combine which replaces sequences |
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222 // of repated increment and decrement commands by appropriate |
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223 // two-character commands. For example for sequences of + |
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224 // |
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225 // orig bf-cmds | replacement |
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226 // ------------------------------ |
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227 // + | +A |
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228 // ++ | +B |
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229 // +++ | +C |
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230 // | |
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231 // ... | |
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232 // | |
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233 // +++....+++ | +Z |
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234 // (where length = 26) |
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235 // |
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236 // Similar for the bf-command -, > and <. All other commands should |
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237 // be unaffected by this change. |
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238 // |
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239 // Adapt the compute4 and run4 functions such that they can deal |
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240 // appropriately with such two-character commands. |
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241 |
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242 def splice(cs: List[Char], acc: List[(Char, Int)]) : List[(Char, Int)] = (cs, acc) match { |
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243 case (Nil, acc) => acc |
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244 case ('[' :: cs, acc) => splice(cs, ('[', 1) :: acc) |
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245 case (']' :: cs, acc) => splice(cs, (']', 1) :: acc) |
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246 case ('.' :: cs, acc) => splice(cs, ('.', 1) :: acc) |
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247 case (',' :: cs, acc) => splice(cs, (',', 1) :: acc) |
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248 case ('0' :: cs, acc) => splice(cs, ('0', 1) :: acc) |
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249 case (c :: cs, Nil) => splice(cs, List((c, 1))) |
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250 case (c :: cs, (d, n) :: acc) => |
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251 if (c == d && n < 26) splice(cs, (c, n + 1) :: acc) |
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252 else splice(cs, (c, 1) :: (d, n) :: acc) |
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253 } |
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254 |
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255 def spl(s: String) = splice(s.toList, Nil).reverse |
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256 |
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257 //spl(load_bff("benchmark.bf")) |
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258 |
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259 def combine(s: String) : String = { |
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260 (for ((c, n) <- spl(s)) yield c match { |
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261 case '>' => List('>', (n + '@').toChar) |
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262 case '<' => List('<', (n + '@').toChar) |
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263 case '+' => List('+', (n + '@').toChar) |
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264 case '-' => List('-', (n + '@').toChar) |
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265 case _ => List(c) |
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266 }).flatten.mkString |
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267 } |
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268 |
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269 |
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270 //combine(load_bff("benchmark.bf")) |
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271 |
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272 def compute4(pg: String, tb: Map[Int, Int], pc: Int, mp: Int, mem: Mem) : Mem = { |
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273 if (0 <= pc && pc < pg.length) { |
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274 val (new_pc, new_mp, new_mem) = pg(pc) match { |
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275 case '0' => (pc + 1, mp, write(mem, mp, 0)) |
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276 case '>' => (pc + 2, mp + (pg(pc + 1) - '@'), mem) |
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277 case '<' => (pc + 2, mp - (pg(pc + 1) - '@'), mem) |
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278 case '+' => (pc + 2, mp, write(mem, mp, sread(mem, mp) + (pg(pc + 1) - '@'))) |
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279 case '-' => (pc + 2, mp, write(mem, mp, sread(mem, mp) - (pg(pc + 1) - '@'))) |
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280 case '.' => { print(sread(mem, mp).toChar); (pc + 1, mp, mem) } |
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281 case ',' => (pc + 1, mp, write(mem, mp, Console.in.read().toByte)) |
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282 case '[' => |
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283 if (sread(mem, mp) == 0) (tb(pc), mp, mem) else (pc + 1, mp, mem) |
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284 case ']' => |
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285 if (sread(mem, mp) != 0) (tb(pc), mp, mem) else (pc + 1, mp, mem) |
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286 case _ => (pc + 1, mp, mem) |
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287 } |
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288 compute4(pg, tb, new_pc, new_mp, new_mem) |
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289 } |
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290 else mem |
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291 } |
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292 |
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293 def run4(pg: String, m: Mem = Map()) = { |
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294 val pg_opt = combine(optimise(pg)) |
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295 compute4(pg_opt, jtable(pg_opt), 0, 0, m) |
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296 } |
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297 |
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298 // testcases |
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299 //combine(optimise(load_bff("benchmark.bf"))) // => """>A+B[<A+M>A-A]<A[[.....""" |
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300 |
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301 //time_needed(1, run4(load_bff("benchmark.bf"))) |
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302 |
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303 //time_needed(1, run(load_bff("sierpinski.bf"))) |
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304 //time_needed(1, run4(load_bff("sierpinski.bf"))) |
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305 |
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306 //time_needed(1, run4(load_bff("mandelbrot.bf"))) |
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307 |
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308 |
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309 } |