Initial data commit

Task/Long-multiplication/C/long-multiplication-1.c

@@ -0,0 +1,55 @@
+#include <stdio.h>
+#include <string.h>
+
+/* c = a * b.  Caller is responsible for memory.
+   c must not be the same as either a or b. */
+void longmulti(const char *a, const char *b, char *c)
+{
+	int i = 0, j = 0, k = 0, n, carry;
+	int la, lb;
+
+	/* either is zero, return "0" */
+	if (!strcmp(a, "0") || !strcmp(b, "0")) {
+		c[0] = '0', c[1] = '\0';
+		return;
+	}
+
+	/* see if either a or b is negative */
+	if (a[0] == '-') { i = 1; k = !k; }
+	if (b[0] == '-') { j = 1; k = !k; }
+
+	/* if yes, prepend minus sign if needed and skip the sign */
+	if (i || j) {
+		if (k) c[0] = '-';
+		longmulti(a + i, b + j, c + k);
+		return;
+	}
+
+	la = strlen(a);
+	lb = strlen(b);
+	memset(c, '0', la + lb);
+	c[la + lb] = '\0';
+
+#	define I(a) (a - '0')
+	for (i = la - 1; i >= 0; i--) {
+		for (j = lb - 1, k = i + j + 1, carry = 0; j >= 0; j--, k--) {
+			n = I(a[i]) * I(b[j]) + I(c[k]) + carry;
+			carry = n / 10;
+			c[k] = (n % 10) + '0';
+		}
+		c[k] += carry;
+	}
+#	undef I
+	if (c[0] == '0') memmove(c, c + 1, la + lb);
+
+	return;
+}
+
+int main()
+{
+	char c[1024];
+	longmulti("-18446744073709551616", "-18446744073709551616", c);
+	printf("%s\n", c);
+
+	return 0;
+}

Task/Long-multiplication/C/long-multiplication-2.c

@@ -0,0 +1 @@
+340282366920938463463374607431768211456