/* roman.c - convert a value to a roman numeral representation */
/* PUBLIC DOMAIN - Jon Mayo - January 31, 2007 */

#include <stdio.h>

static const struct {
    const char *str;
    unsigned val;
} romantab[] = {
    {"M", 1000},
    {"CM", 900},
    {"D", 500},
    {"CD", 400},
    {"C", 100},
    {"XC", 90},
    {"L", 50},
    {"XL", 40},
    {"X", 10},
    {"V", 5},
    {"IV", 4},
    {"I", 1},
    /* we do not walk off the end because of carefully designed code. 
     * changing value>0 to allow the inner for loop to see value as 0 would
     * walk off the end. */
};

/* return 0 on overflow. string won't be null terminated */
int to_roman(char *buf, size_t max, unsigned value) {
    size_t len;
    unsigned rome;
    const char *s;

    rome=0;
    len=0;

    while(value>0) {
        while(romantab[rome].val > value) {
            rome++;
        }
        for(s=romantab[rome].str;*s;s++) {
            if(max<=len) return 0; /* overflow */
            buf[len++]=*s;
        }
        value-=romantab[rome].val;
    }

    if(max<=len) return 0; /* overflow */
    buf[len]=0;

    return len;
}


/* test routine */
#if STAND_ALONE
#include <string.h>
int main() {
    char buf[40];
    memset(buf, '-', sizeof buf); buf[sizeof buf-1]=0;
    printf("result: %d. '%s'\n", to_roman(buf, sizeof buf, 4999), buf);
    memset(buf, '-', sizeof buf); buf[sizeof buf-1]=0;
    printf("result: %d. '%s'\n", to_roman(buf, 4, 4999), buf);
    memset(buf, '-', sizeof buf); buf[sizeof buf-1]=0;
    printf("result: %d. '%s'\n", to_roman(buf, sizeof buf, 1999), buf);
    return 0;
}
#endif