Data commit

Task/Primality-by-trial-division/UNIX-Shell/primality-by-trial-division-1.sh

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+function primep {
+	typeset n=$1 p=3
+	(( n == 2 )) && return 0	# 2 is prime.
+	(( n & 1 )) || return 1		# Other evens are not prime.
+	(( n >= 3 )) || return 1
+
+	# Loop for odd p from 3 to sqrt(n).
+	# Comparing p * p <= n can overflow.
+	while (( p <= n / p )); do
+		# If p divides n, then n is not prime.
+		(( n % p )) || return 1
+		(( p += 2 ))
+	done
+	return 0	# Yes, n is prime.
+}

Task/Primality-by-trial-division/UNIX-Shell/primality-by-trial-division-2.sh

@@ -0,0 +1,15 @@
+primep() {
+	set -- "$1" 3
+	test "$1" -eq 2 && return 0		# 2 is prime.
+	expr "$1" \% 2 >/dev/null || return 1	# Other evens are not prime.
+	test "$1" -ge 3 || return 1
+
+	# Loop for odd p from 3 to sqrt(n).
+	# Comparing p * p <= n can overflow. We use p <= n / p.
+	while expr $2 \<= "$1" / $2 >/dev/null; do
+		# If p divides n, then n is not prime.
+		expr "$1" % $2 >/dev/null || return 1
+		set -- "$1" `expr $2 + 2`
+	done
+	return 0	# Yes, n is prime.
+}