March 2014 update

Task/Fibonacci-sequence/C/fibonacci-sequence-2.c

@@ -5,5 +5,5 @@ long long int fibb(int n) {
 		fnow = fnext;
 		fnext = tempf;
 		}
-		return fnow;	
+		return fnext;	
 }

Task/Fibonacci-sequence/C/fibonacci-sequence-5.c

@@ -0,0 +1,74 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <gmp.h>
+
+typedef struct node node;
+struct node {
+	int n;
+	mpz_t v;
+	node *next;
+};
+
+#define CSIZE 37
+node *cache[CSIZE];
+
+// very primitive linked hash table
+node * find_cache(int n)
+{
+	int idx = n % CSIZE;
+	node *p;
+
+	for (p = cache[idx]; p && p->n != n; p = p->next);
+	if (p) return p;
+
+	p = malloc(sizeof(node));
+	p->next = cache[idx];
+	cache[idx] = p;
+
+	if (n < 2) {
+		p->n = n;
+		mpz_init_set_ui(p->v, 1);
+	} else {
+		p->n = -1; // -1: value not computed yet
+		mpz_init(p->v);
+	}
+	return p;
+}
+
+mpz_t tmp1, tmp2;
+mpz_t *fib(int n)
+{
+	int x;
+	node *p = find_cache(n);
+
+	if (p->n < 0) {
+		p->n = n;
+		x = n / 2;
+
+		mpz_mul(tmp1, *fib(x-1), *fib(n - x - 1));
+		mpz_mul(tmp2, *fib(x), *fib(n - x));
+		mpz_add(p->v, tmp1, tmp2);
+	}
+	return &p->v;
+}
+
+int main(int argc, char **argv)
+{
+	int i, n;
+	if (argc < 2) return 1;
+
+	mpz_init(tmp1);
+	mpz_init(tmp2);
+
+	for (i = 1; i < argc; i++) {
+		n = atoi(argv[i]);
+		if (n < 0) {
+			printf("bad input: %s\n", argv[i]);
+			continue;
+		}
+
+		// about 75% of time is spent in printing
+		gmp_printf("%Zd\n", *fib(n));
+	}
+	return 0;
+}