mcs/class/Mono.Security/Mono.Math.Prime.Generator/SequentialSearchPrimeGeneratorBase.cs

   1 //
   2 // Mono.Math.Prime.Generator.SequentialSearchPrimeGeneratorBase.cs - Prime Generator
   3 //
   4 // Authors:
   5 //      Ben Maurer
   6 //
   7 // Copyright (c) 2003 Ben Maurer. All rights reserved
   8 // Copyright (C) 2004 Novell, Inc (http://www.novell.com)
   9 //
  10 // Permission is hereby granted, free of charge, to any person obtaining
  11 // a copy of this software and associated documentation files (the
  12 // "Software"), to deal in the Software without restriction, including
  13 // without limitation the rights to use, copy, modify, merge, publish,
  14 // distribute, sublicense, and/or sell copies of the Software, and to
  15 // permit persons to whom the Software is furnished to do so, subject to
  16 // the following conditions:
  17 //
  18 // The above copyright notice and this permission notice shall be
  19 // included in all copies or substantial portions of the Software.
  20 //
  21 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  22 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  23 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  24 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  25 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  26 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  27 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  28 //
  29
  30 namespace Mono.Math.Prime.Generator {
  31
  32 #if INSIDE_CORLIB
  33         internal
  34 #else
  35         public
  36 #endif
  37         class SequentialSearchPrimeGeneratorBase : PrimeGeneratorBase {
  38
  39                 protected virtual BigInteger GenerateSearchBase (int bits, object context)
  40                 {
  41                         BigInteger ret = BigInteger.GenerateRandom (bits);
  42                         ret.SetBit (0);
  43                         return ret;
  44                 }
  45
  46
  47                 public override BigInteger GenerateNewPrime (int bits)
  48                 {
  49                         return GenerateNewPrime (bits, null);
  50                 }
  51
  52
  53                 public virtual BigInteger GenerateNewPrime (int bits, object context)
  54                 {
  55                         //
  56                         // STEP 1. Find a place to do a sequential search
  57                         //
  58                         BigInteger curVal = GenerateSearchBase (bits, context);
  59
  60                         const uint primeProd1 = 3u* 5u * 7u * 11u * 13u * 17u * 19u * 23u * 29u;
  61
  62                         uint pMod1 = curVal % primeProd1;
  63
  64                         int DivisionBound = TrialDivisionBounds;
  65                         uint[] SmallPrimes = BigInteger.smallPrimes;
  66                         //
  67                         // STEP 2. Search for primes
  68                         //
  69                         while (true) {
  70
  71                                 //
  72                                 // STEP 2.1 Sieve out numbers divisible by the first 9 primes
  73                                 //
  74                                 if (pMod1 %  3 == 0) goto biNotPrime;
  75                                 if (pMod1 %  5 == 0) goto biNotPrime;
  76                                 if (pMod1 %  7 == 0) goto biNotPrime;
  77                                 if (pMod1 % 11 == 0) goto biNotPrime;
  78                                 if (pMod1 % 13 == 0) goto biNotPrime;
  79                                 if (pMod1 % 17 == 0) goto biNotPrime;
  80                                 if (pMod1 % 19 == 0) goto biNotPrime;
  81                                 if (pMod1 % 23 == 0) goto biNotPrime;
  82                                 if (pMod1 % 29 == 0) goto biNotPrime;
  83
  84                                 //
  85                                 // STEP 2.2 Sieve out all numbers divisible by the primes <= DivisionBound
  86                                 //
  87                                 for (int p = 10; p < SmallPrimes.Length && SmallPrimes [p] <= DivisionBound; p++) {
  88                                         if (curVal % SmallPrimes [p] == 0)
  89                                                 goto biNotPrime;
  90                                 }
  91
  92                                 //
  93                                 // STEP 2.3 Is the potential prime acceptable?
  94                                 //
  95                                 if (!IsPrimeAcceptable (curVal, context))
  96                                         goto biNotPrime;
  97
  98                                 //
  99                                 // STEP 2.4 Filter out all primes that pass this step with a primality test
 100                                 //
 101                                 if (PrimalityTest (curVal, Confidence))
 102                                         return curVal;
 103
 104                                 //
 105                                 // STEP 2.4
 106                                 //
 107                         biNotPrime:
 108                                 pMod1 += 2;
 109                                 if (pMod1 >= primeProd1)
 110                                         pMod1 -= primeProd1;
 111                                 curVal.Incr2 ();
 112                         }
 113                 }
 114
 115                 protected virtual bool IsPrimeAcceptable (BigInteger bi, object context)
 116                 {
 117                         return true;
 118                 }
 119         }
 120 }