1 files changed, 90 insertions, 0 deletions
diff --git a/roman.c b/roman.c
new file mode 100644
index 0000000..6606e25
--- /dev/null
+++ b/roman.c
@@ -0,0 +1,90 @@
+#include <u.h>
+#include <libc.h>
+#include <ctype.h>
+#include "roman.h"
+
+static int decimal[] = {
+	1000, 900,
+	500, 400,
+	100, 90,
+	50, 40,
+	10, 9,
+	5, 4,
+	1
+};
+static char *roman[] = {
+	"M", "CM",
+	"D", "CD",
+	"C", "XC",
+	"L", "XL",
+	"X", "IX",
+	"V", "IV",
+	"I"
+};
+static int alpha2roman[] = {
+	/* A, B,   C,   D, E, F, G, H, I, J, K,  L,    M */
+	   0, 0, 100, 500, 0, 0, 0, 0, 1, 1, 0, 50, 1000,
+	/* N, O, P, Q, R, S, T, U, V, W,  X, Y, Z */
+	   0, 0, 0, 0, 0, 0, 0, 5, 5, 0, 10, 0, 0
+};
+
+
+static int
+getroman(char c)
+{
+	if(!isalpha(c))
+		return -1;
+	return alpha2roman[toupper(c) - 'A'];
+}
+
+int
+dectoroman(int n, char *buf, ulong len)
+{
+	char *p;
+	int i, o;
+
+	o = 0;
+
+	for(i = 0; i < nelem(decimal); i++){
+		while(n >= decimal[i] && o < len-1){
+			for(p = roman[i]; *p != 0 && o < len-1; )
+				buf[o++] = *p++;
+			n -= decimal[i];
+		}
+	}
+	buf[len-1] = 0;
+	return 0;
+}
+
+int
+romantodec(char *buf)
+{
+	char *ebuf, *larger;
+	int curno, largerno, dec;
+
+	ebuf = strchr(buf, '\0');
+	dec = 0;
+
+	while(buf < ebuf){
+		curno = getroman(*buf);
+		if(curno < 0)
+			return -1;
+		larger = buf;
+		do{
+			largerno = getroman(*larger);
+			if(largerno < 0)
+				return -1;
+			if(largerno > curno)
+				break;
+		}while(*++larger != 0);
+		if(*larger == 0)
+			dec += curno;
+		else{
+			dec += largerno;
+			while(buf < larger)
+				dec -= getroman(*buf++);
+		}
+		buf++;
+	}
+	return dec;
+}