Fcalva/chibi-scheme
1
0
Fork 0
mirror of https://github.com/ashinn/chibi-scheme.git synced 2025-05-19 13:49:17 +02:00
Code Issues Projects Releases Packages Wiki Activity Actions

fixing bug in prime-above

Browse source
This commit is contained in:
Alex Shinn 2021-04-14 16:47:29 +09:00
parent 3fc9c22245
commit cfbd64f085
2 changed files with 34 additions and 8 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

12
lib/chibi/math/prime-test.sld
View file

@ -32,7 +32,19 @@
(test 1009 (nth-prime 168)) (test 1009 (nth-prime 168))
(test 1013 (nth-prime 169)) (test 1013 (nth-prime 169))
(test 2 (prime-above 1))
(test 3 (prime-above 2))
(test 5 (prime-above 3))
(test 5 (prime-above 4))
(test 7 (prime-above 5))
(test 907 (prime-above 888)) (test 907 (prime-above 888))
(test 911 (prime-above 907))
(test-not (prime-below 2))
(test 2 (prime-below 3))
(test 3 (prime-below 4))
(test 3 (prime-below 5))
(test 5 (prime-below 6))
(test 5 (prime-below 7))
(test 797 (prime-below 808)) (test 797 (prime-below 808))
(test 1 (totient 2)) (test 1 (totient 2))

30
lib/chibi/math/prime.scm
View file

@ -146,20 +146,34 @@
;;> Returns the first prime less than or equal to \var{n}, or #f if ;;> Returns the first prime less than or equal to \var{n}, or #f if
;;> there are no such primes. ;;> there are no such primes.
(define (prime-below n) (define (prime-below n)
(and (>= n 3) (cond
(let lp ((n (if (even? n) (- n 1) n))) ((> n 3)
(if (prime? n) n (lp (- n 2)))))) (let lp ((n (if (even? n) (- n 1) (- n 2))))
(if (prime? n) n (lp (- n 2)))))
((= n 3)
2)
(else
#f)))
;;> Returns the first prime greater than or equal to \var{n}. If the ;;> Returns the first prime greater than or equal to \var{n}. If the
;;> optional \var{limit} is given and not false, returns \scheme{#f} ;;> optional \var{limit} is given and not false, returns \scheme{#f}
;;> if no such primes exist below \var{limit}. ;;> if no such primes exist below \var{limit}.
(define (prime-above n . o) (define (prime-above n . o)
(let ((limit (and (pair? o) (car o)))) (let ((limit (and (pair? o) (car o))))
(let lp ((n (if (even? n) (+ n 1) n))) (cond
(cond ((< n 2)
((and limit (>= n limit)) #f) 2)
((prime? n) n) (limit
(else (lp (+ n 2))))))) (let lp ((n (if (even? n) (+ n 1) (+ n 2))))
(cond
((>= n limit) #f)
((prime? n) n)
(else (lp (+ n 2))))))
(else
(let lp ((n (if (even? n) (+ n 1) (+ n 2))))
(cond
((prime? n) n)
(else (lp (+ n 2)))))))))
;;> Returns the factorization of \var{n} as a monotonically ;;> Returns the factorization of \var{n} as a monotonically
;;> increasing list of primes. ;;> increasing list of primes.