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Get rid of vector reallocation by preallocating it

db4
Samuel Tardieu 2009-06-24 15:27:58 +02:00
parent 29b5a1dff5
commit 50191588e4
1 changed files with 21 additions and 5 deletions
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26
basis/math/primes/primes.factor
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@ -1,8 +1,9 @@
! Copyright (C) 2007-2009 Samuel Tardieu.
! See http://factorcode.org/license.txt for BSD license.
USING: combinators kernel math math.bitwise math.functions
USING: combinators fry kernel math math.bitwise math.functions
math.order math.primes.erato math.primes.erato.private
math.primes.miller-rabin math.ranges literals random sequences sets ;
math.primes.miller-rabin math.ranges literals random sequences sets
vectors ;
IN: math.primes
<PRIVATE
@ -12,6 +13,21 @@ IN: math.primes
: (prime?) ( n -- ? )
dup 8999999 <= [ look-in-bitmap ] [ miller-rabin ] if ;
! In order not to reallocate large vectors, we compute the upper bound
! of the number of primes in a given interval. We use a double inequality given
! by Pierre Dusart in http://www.ams.org/mathscinet-getitem?mr=99d:11133
! for x > 598. Under this limit, we know that there are at most 108 primes.
: upper-pi ( x -- y )
dup log [ / ] [ 1.2762 swap / 1 + ] bi * ceiling ;
: lower-pi ( x -- y )
dup log [ / ] [ 0.992 swap / 1 + ] bi * floor ;
: <primes-vector> ( low high -- vector )
swap [ [ upper-pi ] [ lower-pi ] bi* - >integer
108 max 10000 min <vector> ] keep
3 < [ [ 2 swap push ] keep ] when ;
PRIVATE>
: prime? ( n -- ? )
@ -29,9 +45,9 @@ PRIVATE>
] if ; foldable
: primes-between ( low high -- seq )
[ dup 3 max dup even? [ 1 + ] when ] dip
2 <range> [ prime? ] filter
swap 3 < [ 2 prefix ] when ;
[ [ 3 max dup even? [ 1 + ] when ] dip 2 <range> ]
[ <primes-vector> ] 2bi
[ '[ [ prime? ] _ push-if ] each ] keep clone ;
: primes-upto ( n -- seq ) 2 swap primes-between ;