lib/libc: Add implementation of strncpy.

lib/libc/string0.c

@@ -169,6 +169,23 @@ char *strcpy(char *dest, const char *src) {
     return dest;
 }
 
+// Public Domain implementation of strncpy from:
+// http://en.wikibooks.org/wiki/C_Programming/Strings#The_strncpy_function
+char *strncpy(char *s1, const char *s2, size_t n) {
+     char *dst = s1;
+     const char *src = s2;
+     /* Copy bytes, one at a time.  */
+     while (n > 0) {
+         n--;
+         if ((*dst++ = *src++) == '\0') {
+             /* If we get here, we found a null character at the end of s2 */
+             *dst = '\0';
+             break;
+         }
+     }
+     return s1;
+ }
+
 // needed because gcc optimises strcpy + strcat to this
 char *stpcpy(char *dest, const char *src) {
     while (*src) {