From 296a8b84c347f86e6399f6b0bcba6a17170204a5 Mon Sep 17 00:00:00 2001
From: H Hautakoski <henrik@fiktivkod.org>
Date: Tue, 13 Jul 2010 09:43:26 +0200
Subject: [PATCH] problem 25

---
 p25.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)
 create mode 100644 p25.c

diff --git a/p25.c b/p25.c
new file mode 100644
index 0000000..28848ce
--- /dev/null
+++ b/p25.c
@@ -0,0 +1,24 @@
+
+/*
+ * http://projecteuler.net
+ * 
+ * Projecteuler - Problem 25
+ * -----------------------
+ * 2010-07-13 Henrik Hautakoski
+ *
+ * Alot of math, binet's formula
+ */
+
+#include <math.h>
+#include <stdio.h>
+
+#define LOG10PHI 0.20898764024997876221 /* log10((1+sqrt(5))/2) */
+#define MAGIC    0.65051499783199062676 /* |(log10(5) / 2) - 1| */
+
+#define fibolen(n) ((int) ceil(((n) - MAGIC) / LOG10PHI))
+
+int main() {
+    
+    printf("%i\n", fibolen(1000));
+    return 0;
+}