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Contents
(defpackage #:sieve
(:use #:cl)
(:export #:primes-to)
(:documentation "Generates a list of primes up to a given limit."))
(in-package #:sieve)
(defun primes-to (n)
"List primes below `n' using sieve of Eratosthenes."
(loop
initially (when (< n 3) (return nil))
with sqrtn = (1+ (isqrt n))
with sieve = (make-array n
:element-type 'boolean
:initial-element t)
for maybe from 2 to sqrtn
when (aref sieve maybe)
do
(loop
for multi from (* maybe maybe) below n by maybe
when (aref sieve multi)
do (setf (aref sieve multi) nil))
finally (return
(loop
for index from 2 below n
when (aref sieve index)
collect index))))
Version data entries
300 entries across 300 versions & 1 rubygems