Class: Distribution::MathExtension::SwingFactorial
- Defined in:
- lib/distribution/math_extension.rb
Overview
Factorization based on Prime Swing algorithm, by Luschny (the king of factorial numbers analysis :P )
Reference
-
The Homepage of Factorial Algorithms. © Peter Luschny, 2000-2010
URL: www.luschny.de/math/factorial/csharp/FactorialPrimeSwing.cs.html
Constant Summary collapse
- SmallOddSwing =
[ 1, 1, 1, 3, 3, 15, 5, 35, 35, 315, 63, 693, 231, 3003, 429, 6435, 6435, 109395, 12155, 230945, 46189, 969969, 88179, 2028117, 676039, 16900975, 1300075, 35102025, 5014575,145422675, 9694845, 300540195, 300540195]
- SmallFactorial =
[1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800, 39916800, 479001600, 6227020800, 87178291200, 1307674368000, 20922789888000, 355687428096000, 6402373705728000, 121645100408832000, 2432902008176640000]
Instance Attribute Summary collapse
-
#result ⇒ Object
readonly
Returns the value of attribute result.
Class Method Summary collapse
Instance Method Summary collapse
- #bitcount(n) ⇒ Object
- #get_primorial(low, up) ⇒ Object
-
#initialize(n) ⇒ SwingFactorial
constructor
A new instance of SwingFactorial.
- #naive_factorial(n) ⇒ Object
- #recfactorial(n) ⇒ Object
- #swing(n) ⇒ Object
Constructor Details
#initialize(n) ⇒ SwingFactorial
Returns a new instance of SwingFactorial.
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# File 'lib/distribution/math_extension.rb', line 81 def initialize(n) if (n<20) @result=SmallFactorial[n] #naive_factorial(n) else @prime_list=[] exp2 = n - bitcount(n); @result= recfactorial(n)<< exp2 end end |
Instance Attribute Details
#result ⇒ Object (readonly)
Returns the value of attribute result.
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# File 'lib/distribution/math_extension.rb', line 69 def result @result end |
Class Method Details
.naive_factorial(n) ⇒ Object
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# File 'lib/distribution/math_extension.rb', line 137 def self.naive_factorial(n) (2..n).inject(1) { |f,nn| f * nn } end |
Instance Method Details
#bitcount(n) ⇒ Object
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# File 'lib/distribution/math_extension.rb', line 72 def bitcount(n) bc = n - ((n >> 1) & 0x55555555); bc = (bc & 0x33333333) + ((bc >> 2) & 0x33333333); bc = (bc + (bc >> 4)) & 0x0f0f0f0f; bc += bc >> 8; bc += bc >> 16; bc = bc & 0x3f; bc end |
#get_primorial(low, up) ⇒ Object
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# File 'lib/distribution/math_extension.rb', line 126 def get_primorial(low,up) prod=1; Prime.each(up) do |prime| next if prime<low prod*=prime end prod end |
#naive_factorial(n) ⇒ Object
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# File 'lib/distribution/math_extension.rb', line 134 def naive_factorial(n) @result=(self.class).naive_factorial(n) end |
#recfactorial(n) ⇒ Object
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# File 'lib/distribution/math_extension.rb', line 91 def recfactorial(n) return 1 if n<2 (recfactorial(n/2)**2) * swing(n) end |
#swing(n) ⇒ Object
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# File 'lib/distribution/math_extension.rb', line 95 def swing(n) return SmallOddSwing[n] if (n<33) sqrtN = Math.sqrt(n).floor count=0 Prime.each(n/3) do |prime| next if prime<3 if (prime<=sqrtN) q=n _p=1 while((q=(q/prime).truncate)>0) do if((q%2)==1) _p*=prime end end if _p>1 @prime_list[count]=_p count+=1 end else if ((n/prime).truncate%2==1) @prime_list[count]=prime count+=1 end end end prod=get_primorial((n/2).truncate+1,n) prod * @prime_list[0,count].inject(1) {|ac,v| ac*v} end |