44 lines
1.1 KiB
Factor
44 lines
1.1 KiB
Factor
! Copyright (c) 2007 Samuel Tardieu.
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! See http://factorcode.org/license.txt for BSD license.
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USING: accessors bit-arrays fry kernel lists.lazy math math.functions
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math.primes.list math.ranges sequences ;
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IN: math.erato
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<PRIVATE
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TUPLE: erato limit bits latest ;
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: ind ( n -- i )
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2/ 1- ; inline
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: is-prime ( n limit -- bool )
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[ ind ] [ bits>> ] bi* nth ; inline
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: indices ( n erato -- range )
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limit>> ind over 3 * ind spin <range> ;
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: mark-multiples ( n erato -- )
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2dup [ sq ] [ limit>> ] bi* <= [
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[ indices ] keep bits>> '[ _ f -rot set-nth ] each
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] [ 2drop ] if ;
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: <erato> ( n -- erato )
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dup ind 1+ <bit-array> dup set-bits 1 erato boa ;
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: next-prime ( erato -- prime/f )
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[ 2 + ] change-latest [ latest>> ] keep
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2dup limit>> <= [
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2dup is-prime [ dupd mark-multiples ] [ nip next-prime ] if
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] [
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2drop f
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] if ;
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PRIVATE>
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: lerato ( n -- lazy-list )
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dup 1000003 < [
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0 primes-under-million seq>list swap '[ _ <= ] lwhile
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] [
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<erato> 2 [ drop next-prime ] with lfrom-by [ ] lwhile
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] if ;
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