1 files changed, 103 insertions, 0 deletions
diff --git a/writeups/multiprecision/fibo-crude-mp.c b/writeups/multiprecision/fibo-crude-mp.c
new file mode 100644
index 0000000..c6a5b7f
--- /dev/null
+++ b/writeups/multiprecision/fibo-crude-mp.c
@@ -0,0 +1,103 @@
+#include <stdio.h>
+#include <stdbool.h>
+#include <string.h>
+#include <assert.h>
+
+#define N 101
+#define MAX_CHAR 256
+
+void do_ieee754 (void) {
+	double a = 0.0;
+	double b = 1.0;
+	double c;
+
+	for (int i = 0; i < N; i += 1) {
+		c = a + b;
+		printf("%.0lf\n", c);
+		b = a;
+		a = c;
+	}
+}
+
+void add (char *out, const char *a, const char *b) {
+	int i;
+	int n;
+	int carry = 0;
+	bool flag;
+
+	for (i = 0; i < MAX_CHAR - 1; i += 1) {
+		n = carry;
+		flag = false;
+		if (a[i] != 0) {
+			n += a[i] - '0';
+			flag = true;
+		}
+		if (b[i] != 0) {
+			n += b[i] - '0';
+			flag = true;
+		}
+		carry = n / 10;
+		if (!flag && carry == 0 && n == 0) {
+			out[i] = 0;
+			return;
+		}
+
+		out[i] = (n % 10) + '0';
+	}
+
+	assert(carry == 0); // detect "overflow"
+}
+
+void print_reversed (const char *s) {
+	const size_t l = strlen(s);
+	const char *p = s + l;
+
+	for (size_t i = 0; i < l; i += 1) {
+		p -= 1;
+		putchar(*p);
+	}
+	putchar('\n');
+}
+
+void do_crude_mp (void) {
+	static char a[MAX_CHAR];
+	static char b[MAX_CHAR];
+	static char c[MAX_CHAR];
+
+	strcpy(a, "0");
+	strcpy(b, "1");
+	memset(c, 0, MAX_CHAR);
+
+	for (int i = 0; i < N; i += 1) {
+		add(c, a, b); // c = a + b;
+		print_reversed(c);
+		memcpy(b, a, MAX_CHAR); // b = a;
+		memcpy(a, c, MAX_CHAR); // a = c;
+	}
+}
+
+bool parse_flag (const char *s) {
+	if (strcmp(s, "true") == 0) {
+		return true;
+	}
+	else if (strcmp(s, "false") == 0) {
+		return false;
+	}
+	else {
+		double tmp = 0.0;
+
+		sscanf(s, "%lf", &tmp);
+		return tmp != 0.0;
+	}
+}
+
+int main (const int argc, const char **argv) {
+	if (argc == 1 || (argc > 1 && parse_flag(argv[1]))) {
+		do_crude_mp();
+	}
+	else {
+		do_ieee754();
+	}
+
+	return 0;
+}