Add libmp.

src/libmp/port/mpvecadd.c

@@ -0,0 +1,35 @@
+#include "os.h"
+#include <mp.h>
+#include "dat.h"
+
+// prereq: alen >= blen, sum has at least blen+1 digits
+void
+mpvecadd(mpdigit *a, int alen, mpdigit *b, int blen, mpdigit *sum)
+{
+	int i, carry;
+	mpdigit x, y;
+
+	carry = 0;
+	for(i = 0; i < blen; i++){
+		x = *a++;
+		y = *b++;
+		x += carry;
+		if(x < carry)
+			carry = 1;
+		else
+			carry = 0;
+		x += y;
+		if(x < y)
+			carry++;
+		*sum++ = x;
+	}
+	for(; i < alen; i++){
+		x = *a++ + carry;
+		if(x < carry)
+			carry = 1;
+		else
+			carry = 0;
+		*sum++ = x;
+	}
+	*sum = carry;
+}