New function 'lua_numbertostrbuff'

It converts a Lua number to a string in a buffer, without creating
a new Lua string.

liolib.c

@@ -665,20 +665,16 @@ static int g_write (lua_State *L, FILE *f, int arg) {
   int status = 1;
   errno = 0;
   for (; nargs--; arg++) {
-    if (lua_type(L, arg) == LUA_TNUMBER) {
-      /* optimization: could be done exactly as for strings */
-      int len = lua_isinteger(L, arg)
-                ? fprintf(f, LUA_INTEGER_FMT,
-                             (LUAI_UACINT)lua_tointeger(L, arg))
-                : fprintf(f, LUA_NUMBER_FMT,
-                             (LUAI_UACNUMBER)lua_tonumber(L, arg));
-      status = status && (len > 0);
-    }
-    else {
-      size_t l;
-      const char *s = luaL_checklstring(L, arg, &l);
-      status = status && (fwrite(s, sizeof(char), l, f) == l);
+    char buff[LUA_N2SBUFFSZ];
+    const char *s;
+    size_t len = lua_numbertostrbuff(L, arg, buff);  /* try as a number */
+    if (len > 0) {  /* did conversion work (value was a number)? */
+      s = buff;
+      len--;
     }
+    else  /* must be a string */
+      s = luaL_checklstring(L, arg, &len);
+    status = status && (fwrite(s, sizeof(char), len, f) == len);
   }
   if (l_likely(status))
     return 1;  /* file handle already on stack top */