C: roman numerals

c/roman-numerals/src/roman_numerals.c

@@ -0,0 +1,77 @@
+#include "roman_numerals.h"
+#include <stdio.h>
+#include <string.h>
+#include <malloc.h>
+
+/* V1: initial working version
+ * V2 & V3: code simplification
+ */
+
+static struct conv_s {
+    unsigned char r;
+    unsigned d;
+} conv[] = {
+    { 'M', 1000 },
+    { 'D',  500 },
+    { 'C',  100 },
+    { 'L',   50 },
+    { 'X',   10 },
+    { 'V',    5 },
+    { 'I',    1 }
+};
+
+/* rules could differ (like IIII/VIIII instead of IV/IX), so it is better not
+ * to harcode values like 4, 9, 40, 90 etc...
+ * Example: the Colosseum gate 44 was written XLIIII, and not XLIV.
+ * we can therefore add a parameter in function below, and add a rule in
+ * the code to easily return a different notation.
+ */
+char *to_roman_numeral(unsigned int n /*, int notation */ )
+{
+    unsigned cur=0, mult, pos=0, i;
+    char res[64]={0}, *to;
+
+    /* max number = 3999 = MMMCMXCIX */
+    if (n >= 4000)                                /* could be different if we */
+        return NULL;                              /* accept the 5000 sign */
+
+    while (n) {
+        /* we could : switch (notation) {
+         *              case ROMAN_RULE:
+         */
+        if ((mult=n/conv[cur].d)) {               /* >= current multiplier */
+            if (mult%5==4) {                      /* 4 & 9 */
+                res[pos++]=conv[cur].r;
+                res[pos++]=conv[cur-mult/4].r;    /* 4/4=1, 9/4=2 */
+            } else {                              /* 1-3 & 5-8 */
+                if (mult >= 5)
+                    res[pos++]=conv[cur-1].r;
+                for (i=mult%5; i>0; --i)
+                    res[pos++]=conv[cur].r;
+            }
+        }
+        n-=mult*conv[cur].d;
+        cur+=2;
+    }
+    if ((to=malloc(pos+1)))
+        memcpy(to, res, pos+1);
+    return to;
+}
+
+
+/* See GNUmakefile below for explanation
+ * https://github.com/braoult/exercism/blob/master/c/templates/GNUmakefile
+ */
+#ifdef UNIT_TEST
+#include <stdlib.h>
+int main(int ac, char **av)
+{
+    int arg=1;
+    unsigned i;
+
+    for (; arg<ac; ++arg) {
+        i=atoi(av[arg]);
+        printf("roman(%d)=%s\n", i, to_roman_numeral(i));
+    }
+}
+#endif