From 2ba8a8aaebb3c49ed8fa2a36b98f8a4d999d7156 Mon Sep 17 00:00:00 2001
From: Henrik Hautakoski <henrik.hautakoski@gmail.com>
Date: Fri, 9 Apr 2010 16:20:42 +0200
Subject: [PATCH] problem 10 done, and problem 7 rewritten (new is_prime
 algorithm)

---
 lib/prime.c | 18 ++++++++++++++++++
 lib/prime.h | 10 ++++++++++
 p10.c       | 25 +++++++++++++++++++++++++
 p7.c        | 47 +++++++++++------------------------------------
 4 files changed, 64 insertions(+), 36 deletions(-)
 create mode 100644 lib/prime.c
 create mode 100644 lib/prime.h
 create mode 100644 p10.c

diff --git a/lib/prime.c b/lib/prime.c
new file mode 100644
index 0000000..fc54d34
--- /dev/null
+++ b/lib/prime.c
@@ -0,0 +1,18 @@
+
+#include "prime.h"
+#include <math.h>
+
+int is_prime(uint32_t p) {
+
+    uint32_t i, l;
+
+    if (p < 2 || (p & 1) == 0)
+        return 0;
+
+    l = ((uint32_t)sqrt(p)) + 1;
+
+    for(i=3; i < l; i+=2)
+        if (p % i == 0) return 0;
+
+    return 1;
+}
diff --git a/lib/prime.h b/lib/prime.h
new file mode 100644
index 0000000..2a5a814
--- /dev/null
+++ b/lib/prime.h
@@ -0,0 +1,10 @@
+
+#ifndef __PRIME_H
+
+#define __PRIME_H
+
+#include <stdint.h>
+
+int is_prime(uint32_t p);
+
+#endif /* __PRIME_H */
diff --git a/p10.c b/p10.c
new file mode 100644
index 0000000..e2ee6fd
--- /dev/null
+++ b/p10.c
@@ -0,0 +1,25 @@
+
+/*
+ * http://projecteuler.net
+ * 
+ * Projecteuler - Problem 10
+ * ------------------------
+ * 2010-04-06 Henrik Hautakoski
+ */
+
+#include <stdio.h>
+#include "lib/prime.h"
+
+int main() {
+
+    uint32_t i;
+    uint64_t s = 2;
+
+    for(i=3; i < 2e6; i+=2) {
+        if (is_prime(i))
+            s += i;
+    }
+    printf("%lli\n", s); /* this format throws som warnings but works so whatever */
+
+    return 0;
+}
diff --git a/p7.c b/p7.c
index 3210c5c..a64e82d 100644
--- a/p7.c
+++ b/p7.c
@@ -5,50 +5,25 @@
  * Projecteuler - Problem 7
  * ------------------------
  * 2009-12-28 Henrik Hautakoski
- * 
- * fast and elegant solution using The fundamental theorem of arithmetic wich state: 
- * any natural number greater than 1 can be prime factorized in only one unique way 
- * unless it is prime itself.
  */
 
 #include <stdio.h>
-#include <malloc.h>
-
-int isprime(int *pl, int l, int p) {
-    
-    int i;	
-	
-	for(i=0; i < l; i++) {
-
-		if((p % pl[i]) == 0)
-			return 0;
-	}
-	
-	return 1;
-}
+#include "lib/prime.h"
 
 int main() {
 	
-    int i, len = 3, *prime = malloc(sizeof(int)*10001);
+    uint32_t i, p, n = 1;
 	
-    if (prime == NULL)
-        return 1;
-    
-    prime[0] = 2;
-    prime[1] = 3;
-    prime[2] = 5;
-    
-	for(i=6; len < 10001; i++) {
-		
-		if(!isprime(prime, len, i))
-			continue;
-		
-		prime[len++] = i;
-	}
+    for(i=3; n < 10001; i+=2) {
 
-	printf("%i\n", prime[len-1]);
-    
-    free(prime);
+        if (!is_prime(i))
+            continue;
+
+        p = i;
+        n++;
+    }
+
+	printf("%i\n", p);
     
 	return 0;
 }