diff options
| author | yugui <yugui@b2dd03c8-39d4-4d8f-98ff-823fe69b080e> | 2013-07-15 04:21:34 +0000 |
|---|---|---|
| committer | yugui <yugui@b2dd03c8-39d4-4d8f-98ff-823fe69b080e> | 2013-07-15 04:21:34 +0000 |
| commit | def83bff91d59fa5fdd1898f903f9000ad1dbe13 () | |
| tree | 8479efc5a3c459e7b10de23660e56517ee691eab /lib/prime.rb | |
| parent | ceda88160167a1f21e668b531ece621eaf2a4951 (diff) | |
* lib/prime.rb (Prime::EratosthenesGenerator,
Prime::EratosthenesSieve): New implementation by robertjlooby <robertjlooby AT gmail.com>. * test/test_prime.rb: updated with new method name commit 4b6090ea852d63b26e02796c69b41caa0fa95077 Merge: ceda881 c8f7809 Author: Yuki Sonoda (Yugui) <[email protected]> Date: Mon Jul 15 12:50:04 2013 +0900 Merge commit 'c8f780987fbdfbae428977487e1cf793c4c36d3f' Conflicts: lib/prime.rb commit c8f780987fbdfbae428977487e1cf793c4c36d3f Author: robertjlooby <[email protected]> Date: Thu Jun 27 23:04:45 2013 -0500 updated test/test_prime.rb with new method name commit 996517bdbb3108cd1687d99613b69e539eb1567b Author: robertjlooby <[email protected]> Date: Thu Jun 27 22:59:39 2013 -0500 new implementation of Prime::EratosthenesGenerator and Prime::EratosthenesSieve git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41982 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
| -rw-r--r-- | lib/prime.rb | 93 |
1 files changed, 37 insertions, 56 deletions
@@ -306,12 +306,13 @@ class Prime # Uses +EratosthenesSieve+. class EratosthenesGenerator < PseudoPrimeGenerator def initialize - @last_prime = nil super end def succ - @last_prime = @last_prime ? EratosthenesSieve.instance.next_to(@last_prime) : 2 end def rewind initialize @@ -422,68 +423,48 @@ class Prime class EratosthenesSieve include Singleton - BITS_PER_ENTRY = 16 # each entry is a set of 16-bits in a Fixnum - NUMS_PER_ENTRY = BITS_PER_ENTRY * 2 # twiced because even numbers are omitted - ENTRIES_PER_TABLE = 8 - NUMS_PER_TABLE = NUMS_PER_ENTRY * ENTRIES_PER_TABLE - FILLED_ENTRY = (1 << NUMS_PER_ENTRY) - 1 - - def initialize # :nodoc: - # bitmap for odd prime numbers less than 256. - # For an arbitrary odd number n, @tables[i][j][k] is - # * 1 if n is prime, - # * 0 if n is composite, - # where i,j,k = indices(n) - @tables = [[0xcb6e, 0x64b4, 0x129a, 0x816d, 0x4c32, 0x864a, 0x820d, 0x2196].freeze] end - # returns the least odd prime number which is greater than +n+. - def next_to(n) - n = (n-1).div(2)*2+3 # the next odd number to given n - table_index, integer_index, bit_index = indices(n) - loop do - extend_table until @tables.length > table_index - for j in integer_index...ENTRIES_PER_TABLE - if !@tables[table_index][j].zero? - for k in bit_index...BITS_PER_ENTRY - return NUMS_PER_TABLE*table_index + NUMS_PER_ENTRY*j + 2*k+1 if !@tables[table_index][j][k].zero? - end - end - bit_index = 0 - end - table_index += 1; integer_index = 0 - end end private - # for an odd number +n+, returns (i, j, k) such that @tables[i][j][k] represents primality of the number - def indices(n) - # binary digits of n: |0|1|2|3|4|5|6|7|8|9|10|11|.... - # indices: |-| k | j | i - # because of NUMS_PER_ENTRY, NUMS_PER_TABLE - - k = (n & 0b00011111) >> 1 - j = (n & 0b11100000) >> 5 - i = n >> 8 - return i, j, k - end - def extend_table - lbound = NUMS_PER_TABLE * @tables.length - ubound = lbound + NUMS_PER_TABLE - new_table = [FILLED_ENTRY] * ENTRIES_PER_TABLE # which represents primality in lbound...ubound - (3..Integer(Math.sqrt(ubound))).step(2) do |p| - i, j, k = indices(p) - next if @tables[i][j][k].zero? - - start = (lbound.div(p)+1)*p # least multiple of p which is >= lbound - start += p if start.even? - (start...ubound).step(2*p) do |n| - _, j, k = indices(n) - new_table[j] &= FILLED_ENTRY^(1<<k) end end - @tables << new_table.freeze end end |