From d92ef2124ca767de0748082b41692405e8b95afd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dominik=20Pant=C5=AF=C4=8Dek?=
 <dominik.pantucek@trustica.cz>
Date: Thu, 16 Mar 2023 22:24:24 +0100
Subject: [PATCH] Add primes module skeleton.

---
 primes.scm | 85 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)
 create mode 100644 primes.scm

diff --git a/primes.scm b/primes.scm
new file mode 100644
index 0000000..d08f9b0
--- /dev/null
+++ b/primes.scm
@@ -0,0 +1,85 @@
+;;
+;; primes.scm
+;;
+;; Simple handling of 4-digit primes.
+;;
+;; ISC License
+;;
+;; Copyright 2023 Brmlab, z.s.
+;; Dominik Pantůček <dominik.pantucek@trustica.cz>
+;;
+;; Permission to use, copy, modify, and/or distribute this software
+;; for any purpose with or without fee is hereby granted, provided
+;; that the above copyright notice and this permission notice appear
+;; in all copies.
+;; 
+;; THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+;; WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+;; WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
+;; AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR
+;; CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+;; OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
+;; NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+;; CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+;;
+
+(declare (unit primes))
+
+(module
+ primes
+ (primes-tests!)
+
+ (import scheme
+	 (chicken base)
+	 testing)
+
+ ;; Checks whether given number is prime by checking the remainder of
+ ;; the division by all primes less than square root of the number in
+ ;; question.
+ (define (check-prime primes n)
+   (let ((prime-at-most
+	  (inexact->exact
+	   (floor
+	    (sqrt n)))))
+     (let loop ((ps primes))
+       (if (null? ps)
+	   #t
+	   (let ((cp (car ps)))
+	     (if (<= cp prime-at-most)
+		 (if (eq? (remainder n cp) 0)
+		     #f
+		     (loop (cdr ps)))
+		 #t))))))
+
+ ;; Generates list of primes less than given argument.
+ (define (gen-primes less-than)
+   (let loop ((primes '(2))
+	      (number 3))
+     (if (< number less-than)
+	 (loop (if (check-prime primes number)
+		   (append primes (list number))
+		   primes)
+	       (+ number 2))
+	 primes)))
+
+ ;; Used for checking any primes < 10000
+ (define primes<100 (gen-primes 100))
+
+ ;; Check whether given number is four-digit number and whether it is
+ ;; also prime.
+ (define (is-4digit-prime? n)
+   (and (>= n 1000)
+	(<= n 9999)
+	(check-prime primes<100 n)))
+
+ ;; Module self-tests.
+ (define (primes-tests!)
+   (run-tests
+    primes
+    ))
+
+ )
+
+(import primes)
+
+(primes-tests!)