1 | #!./perl |
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2 | |
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3 | # From Tom Phoenix <rootbeer@teleport.com> 22 Feb 1997 |
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4 | # Based upon a test script by kgb@ast.cam.ac.uk (Karl Glazebrook) |
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5 | |
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6 | # Looking for the hints? You're in the right place. |
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7 | # The hints are near each test, so search for "TEST #", where |
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8 | # the pound sign is replaced by the number of the test. |
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9 | |
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10 | # I'd like to include some more robust tests, but anything |
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11 | # too subtle to be detected here would require a time-consuming |
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12 | # test. Also, of course, we're here to detect only flaws in Perl; |
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13 | # if there are flaws in the underlying system rand, that's not |
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14 | # our responsibility. But if you want better tests, see |
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15 | # The Art of Computer Programming, Donald E. Knuth, volume 2, |
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16 | # chapter 3. ISBN 0-201-03822-6 (v. 2) |
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17 | |
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18 | BEGIN { |
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19 | chdir "t" if -d "t"; |
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20 | @INC = qw(. ../lib); |
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21 | } |
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22 | |
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23 | use strict; |
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24 | use Config; |
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25 | |
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26 | require "test.pl"; |
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27 | plan(tests => 8); |
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28 | |
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29 | |
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30 | my $reps = 10000; # How many times to try rand each time. |
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31 | # May be changed, but should be over 500. |
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32 | # The more the better! (But slower.) |
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33 | |
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34 | sub bits ($) { |
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35 | # Takes a small integer and returns the number of one-bits in it. |
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36 | my $total; |
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37 | my $bits = sprintf "%o", $_[0]; |
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38 | while (length $bits) { |
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39 | $total += (0,1,1,2,1,2,2,3)[chop $bits]; # Oct to bits |
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40 | } |
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41 | $total; |
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42 | } |
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43 | |
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44 | # First, let's see whether randbits is set right |
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45 | { |
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46 | my($max, $min, $sum); # Characteristics of rand |
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47 | my($off, $shouldbe); # Problems with randbits |
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48 | my($dev, $bits); # Number of one bits |
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49 | my $randbits = $Config{randbits}; |
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50 | $max = $min = rand(1); |
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51 | for (1..$reps) { |
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52 | my $n = rand(1); |
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53 | if ($n < 0.0 or $n >= 1.0) { |
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54 | print <<EOM; |
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55 | # WHOA THERE! \$Config{drand01} is set to '$Config{drand01}', |
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56 | # but that apparently produces values < 0.0 or >= 1.0. |
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57 | # Make sure \$Config{drand01} is a valid expression in the |
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58 | # C-language, and produces values in the range [0.0,1.0). |
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59 | # |
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60 | # I give up. |
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61 | EOM |
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62 | exit; |
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63 | } |
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64 | $sum += $n; |
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65 | $bits += bits($n * 256); # Don't be greedy; 8 is enough |
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66 | # It's too many if randbits is less than 8! |
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67 | # But that should never be the case... I hope. |
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68 | # Note: If you change this, you must adapt the |
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69 | # formula for absolute standard deviation, below. |
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70 | $max = $n if $n > $max; |
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71 | $min = $n if $n < $min; |
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72 | } |
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73 | |
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74 | |
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75 | # This test checks for one of Perl's most frequent |
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76 | # mis-configurations. Your system's documentation |
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77 | # for rand(2) should tell you what value you need |
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78 | # for randbits. Usually the diagnostic message |
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79 | # has the right value as well. Just fix it and |
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80 | # recompile, and you'll usually be fine. (The main |
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81 | # reason that the diagnostic message might get the |
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82 | # wrong value is that Config.pm is incorrect.) |
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83 | # |
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84 | unless (ok( !$max <= 0 or $max >= (2 ** $randbits))) {# Just in case... |
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85 | print <<DIAG; |
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86 | # max=[$max] min=[$min] |
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87 | # This perl was compiled with randbits=$randbits |
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88 | # which is _way_ off. Or maybe your system rand is broken, |
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89 | # or your C compiler can't multiply, or maybe Martians |
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90 | # have taken over your computer. For starters, see about |
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91 | # trying a better value for randbits, probably smaller. |
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92 | DIAG |
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93 | |
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94 | # If that isn't the problem, we'll have |
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95 | # to put d_martians into Config.pm |
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96 | print "# Skipping remaining tests until randbits is fixed.\n"; |
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97 | exit; |
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98 | } |
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99 | |
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100 | $off = log($max) / log(2); # log2 |
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101 | $off = int($off) + ($off > 0); # Next more positive int |
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102 | unless (is( $off, 0 )) { |
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103 | $shouldbe = $Config{randbits} + $off; |
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104 | print "# max=[$max] min=[$min]\n"; |
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105 | print "# This perl was compiled with randbits=$randbits on $^O.\n"; |
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106 | print "# Consider using randbits=$shouldbe instead.\n"; |
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107 | # And skip the remaining tests; they would be pointless now. |
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108 | print "# Skipping remaining tests until randbits is fixed.\n"; |
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109 | exit; |
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110 | } |
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111 | |
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112 | |
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113 | # This should always be true: 0 <= rand(1) < 1 |
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114 | # If this test is failing, something is seriously wrong, |
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115 | # either in perl or your system's rand function. |
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116 | # |
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117 | unless (ok( !($min < 0 or $max >= 1) )) { # Slightly redundant... |
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118 | print "# min too low\n" if $min < 0; |
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119 | print "# max too high\n" if $max >= 1; |
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120 | } |
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121 | |
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122 | |
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123 | # This is just a crude test. The average number produced |
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124 | # by rand should be about one-half. But once in a while |
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125 | # it will be relatively far away. Note: This test will |
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126 | # occasionally fail on a perfectly good system! |
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127 | # See the hints for test 4 to see why. |
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128 | # |
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129 | $sum /= $reps; |
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130 | unless (ok( !($sum < 0.4 or $sum > 0.6) )) { |
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131 | print "# Average random number is far from 0.5\n"; |
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132 | } |
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133 | |
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134 | |
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135 | # NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE |
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136 | # This test will fail .1% of the time on a normal system. |
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137 | # also |
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138 | # This test asks you to see these hints 100% of the time! |
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139 | # NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE |
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140 | # |
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141 | # There is probably no reason to be alarmed that |
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142 | # something is wrong with your rand function. But, |
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143 | # if you're curious or if you can't help being |
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144 | # alarmed, keep reading. |
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145 | # |
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146 | # This is a less-crude test than test 3. But it has |
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147 | # the same basic flaw: Unusually distributed random |
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148 | # values should occasionally appear in every good |
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149 | # random number sequence. (If you flip a fair coin |
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150 | # twenty times every day, you'll see it land all |
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151 | # heads about one time in a million days, on the |
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152 | # average. That might alarm you if you saw it happen |
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153 | # on the first day!) |
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154 | # |
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155 | # So, if this test failed on you once, run it a dozen |
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156 | # times. If it keeps failing, it's likely that your |
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157 | # rand is bogus. If it keeps passing, it's likely |
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158 | # that the one failure was bogus. If it's a mix, |
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159 | # read on to see about how to interpret the tests. |
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160 | # |
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161 | # The number printed in square brackets is the |
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162 | # standard deviation, a statistical measure |
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163 | # of how unusual rand's behavior seemed. It should |
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164 | # fall in these ranges with these *approximate* |
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165 | # probabilities: |
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166 | # |
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167 | # under 1 68.26% of the time |
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168 | # 1-2 27.18% of the time |
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169 | # 2-3 4.30% of the time |
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170 | # over 3 0.26% of the time |
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171 | # |
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172 | # If the numbers you see are not scattered approximately |
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173 | # (not exactly!) like that table, check with your vendor |
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174 | # to find out what's wrong with your rand. Or with this |
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175 | # algorithm. :-) |
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176 | # |
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177 | # Calculating absoulute standard deviation for number of bits set |
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178 | # (eight bits per rep) |
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179 | $dev = abs ($bits - $reps * 4) / sqrt($reps * 2); |
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180 | |
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181 | ok( $dev < 3.3 ); |
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182 | |
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183 | if ($dev < 1.96) { |
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184 | print "# Your rand seems fine. If this test failed\n"; |
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185 | print "# previously, you may want to run it again.\n"; |
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186 | } elsif ($dev < 2.575) { |
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187 | print "# This is ok, but suspicious. But it will happen\n"; |
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188 | print "# one time out of 25, more or less.\n"; |
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189 | print "# You should run this test again to be sure.\n"; |
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190 | } elsif ($dev < 3.3) { |
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191 | print "# This is very suspicious. It will happen only\n"; |
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192 | print "# about one time out of 100, more or less.\n"; |
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193 | print "# You should run this test again to be sure.\n"; |
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194 | } elsif ($dev < 3.9) { |
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195 | print "# This is VERY suspicious. It will happen only\n"; |
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196 | print "# about one time out of 1000, more or less.\n"; |
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197 | print "# You should run this test again to be sure.\n"; |
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198 | } else { |
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199 | print "# This is VERY VERY suspicious.\n"; |
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200 | print "# Your rand seems to be bogus.\n"; |
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201 | } |
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202 | print "#\n# If you are having random number troubles,\n"; |
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203 | print "# see the hints within the test script for more\n"; |
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204 | printf "# information on why this might fail. [ %.3f ]\n", $dev; |
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205 | } |
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206 | |
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207 | |
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208 | # Now, let's see whether rand accepts its argument |
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209 | { |
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210 | my($max, $min); |
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211 | $max = $min = rand(100); |
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212 | for (1..$reps) { |
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213 | my $n = rand(100); |
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214 | $max = $n if $n > $max; |
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215 | $min = $n if $n < $min; |
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216 | } |
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217 | |
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218 | # This test checks to see that rand(100) really falls |
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219 | # within the range 0 - 100, and that the numbers produced |
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220 | # have a reasonably-large range among them. |
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221 | # |
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222 | unless ( ok( !($min < 0 or $max >= 100 or ($max - $min) < 65) ) ) { |
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223 | print "# min too low\n" if $min < 0; |
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224 | print "# max too high\n" if $max >= 100; |
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225 | print "# range too narrow\n" if ($max - $min) < 65; |
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226 | } |
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227 | |
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228 | |
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229 | # This test checks that rand without an argument |
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230 | # is equivalent to rand(1). |
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231 | # |
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232 | $_ = 12345; # Just for fun. |
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233 | srand 12345; |
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234 | my $r = rand; |
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235 | srand 12345; |
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236 | is(rand(1), $r, 'rand() without args is rand(1)'); |
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237 | |
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238 | |
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239 | # This checks that rand without an argument is not |
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240 | # rand($_). (In case somebody got overzealous.) |
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241 | # |
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242 | ok($r < 1, 'rand() without args is under 1'); |
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243 | } |
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244 | |
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