5 files changed, 148 insertions, 0 deletions
diff --git a/mkfile b/mkfile
new file mode 100644
index 0000000..134694d
--- /dev/null
+++ b/mkfile
@@ -0,0 +1,9 @@
+</$objtype/mkfile
+
+LIB=libroman.a$O
+OFILES=\
+	roman.$O\
+
+HFILES=roman.h
+
+</sys/src/cmd/mklib
diff --git a/readme.md b/readme.md
new file mode 100644
index 0000000..99724a2
--- /dev/null
+++ b/readme.md
@@ -0,0 +1,3 @@
+# libroman
+
+A library to convert between roman and decimal numbers.
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;
+}
diff --git a/roman.h b/roman.h
new file mode 100644
index 0000000..f105ede
--- /dev/null
+++ b/roman.h
@@ -0,0 +1,2 @@
+int dectoroman(int, char*, ulong);
+int romantodec(char*);
diff --git a/test.c b/test.c
new file mode 100644
index 0000000..fb71a58
--- /dev/null
+++ b/test.c
@@ -0,0 +1,44 @@
+#include <u.h>
+#include <libc.h>
+#include "roman.h"
+
+void
+usage(void)
+{
+	fprint(2, "usage: %s [ -dr ] number\n", argv0);
+	exits("usage");
+}
+
+void
+main(int argc, char *argv[])
+{
+	int decimal;
+	char *roman, buf[512];
+
+	decimal = -1;
+	roman = nil;
+
+	ARGBEGIN{
+	case 'd':
+		roman = EARGF(usage());
+		break;
+	case 'r':
+		decimal = strtol(EARGF(usage()), nil, 10);
+		break;
+	}ARGEND;
+	if(argc != 0)
+		usage();
+
+	if(decimal >= 0){
+		if(dectoroman(decimal, buf, sizeof buf) < 0)
+			sysfatal("dectoroman: %r");
+		print("%s\n", buf);
+	}else if(roman != nil){
+		if((decimal = romantodec(roman)) < 0)
+			sysfatal("romantodec: %r");
+		print("%d\n", decimal);
+	}else
+		usage();
+
+	exits(nil);
+}