Function prepbuffsize

third-party/lua-5.5.0/src/lauxlib.c:564–587

** Returns a pointer to a free area with at least 'sz' bytes in buffer ** 'B'. 'boxidx' is the relative position in the stack where is the ** buffer's box or its placeholder. */

** buffer's box or its placeholder.
*/
static char *prepbuffsize (luaL_Buffer *B, size_t sz, int boxidx) {
  checkbufferlevel(B, boxidx);
  if (B->size - B->n >= sz)  /* enough space? */
    return B->b + B->n;
  else {
    lua_State *L = B->L;
    char *newbuff;
    size_t newsize = newbuffsize(B, sz);
    /* create larger buffer */
    if (buffonstack(B))  /* buffer already has a box? */
      newbuff = (char *)resizebox(L, boxidx, newsize);  /* resize it */
    else {  /* no box yet */
      lua_remove(L, boxidx);  /* remove placeholder */
      newbox(L);  /* create a new box */
      lua_insert(L, boxidx);  /* move box to its intended position */
      lua_toclose(L, boxidx);
      newbuff = (char *)resizebox(L, boxidx, newsize);
      memcpy(newbuff, B->b, B->n * sizeof(char));  /* copy original content */
    }
    B->b = newbuff;
    B->size = newsize;
    return newbuff + B->n;
  }
}

/*
** returns a pointer to a free area with at least 'sz' bytes