26 lines
692 B
Factor
26 lines
692 B
Factor
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! Copyright (C) 2009 Samuel Tardieu.
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! See http://factorcode.org/license.txt for BSD license.
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USING: bit-arrays kernel math math.functions math.ranges sequences ;
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IN: math.primes.erato
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: >index ( n -- i )
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3 - 2 /i ; inline
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: index> ( i -- n )
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2 * 3 + ; inline
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: mark-multiples ( i arr -- )
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[ index> [ sq >index ] keep ] dip
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[ length 1 - swap <range> f swap ] keep
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[ set-nth ] curry with each ;
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: maybe-mark-multiples ( i arr -- )
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2dup nth [ mark-multiples ] [ 2drop ] if ;
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: init-sieve ( n -- arr )
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>index 1 + <bit-array> dup set-bits ;
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: sieve ( n -- arr )
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[ init-sieve ] [ sqrt >index [0,b] ] bi
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over [ maybe-mark-multiples ] curry each ; foldable
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