/* Push formatted message as a string object to Lua stack. va_list variant. */
const char *lj_str_pushvf(lua_State *L, const char *fmt, va_list argp)
{
  SBuf *sb = &G(L)->tmpbuf;
  lj_str_needbuf(L, sb, (MSize)strlen(fmt));
  lj_str_resetbuf(sb);
  for (;;) {
    const char *e = strchr(fmt, '%');
    if (e == NULL) break;
    addstr(L, sb, fmt, (MSize)(e-fmt));
    /* This function only handles %s, %c, %d, %f and %p formats. */
    switch (e[1]) {
    case 's': {
      const char *s = va_arg(argp, char *);
      if (s == NULL) s = "(null)";
      addstr(L, sb, s, (MSize)strlen(s));
      break;
      }
    case 'c':
      addchar(L, sb, va_arg(argp, int));
      break;
    case 'd': {
      char buff[1+10];
      char *p = buff+sizeof(buff);
      int32_t k = va_arg(argp, int32_t);
      uint32_t i = (uint32_t)(k < 0 ? -k : k);
      do { *--p = (char)('0' + i % 10); } while (i /= 10);
      if (k < 0) *--p = '-';
      addstr(L, sb, p, (MSize)(buff+sizeof(buff)-p));
      break;
      }
    case 'f': {
      char buf[LUAI_MAXNUMBER2STR];
      TValue tv;
      MSize len;
      tv.n = cast_num(va_arg(argp, LUAI_UACNUMBER));
      len = (MSize)lj_str_bufnum(buf, &tv);
      addstr(L, sb, buf, len);
      break;
      }
    case 'p': {
#define FMTP_CHARS  (2*sizeof(ptrdiff_t))
      char buff[2+FMTP_CHARS];
      ptrdiff_t p = (ptrdiff_t)(va_arg(argp, void *));
      ptrdiff_t i, lasti = 2+FMTP_CHARS;
#if LJ_64
      if ((p >> 32) == 0)  /* Shorten output for true 32 bit pointers. */
    lasti = 2+2*4;
#endif
      buff[0] = '0';
      buff[1] = 'x';
      for (i = lasti-1; i >= 2; i--, p >>= 4)
    buff[i] = "0123456789abcdef"[(p & 15)];
      addstr(L, sb, buff, (MSize)lasti);
      break;
      }
    case '%':
      addchar(L, sb, '%');
      break;
    default:
      addchar(L, sb, '%');
      addchar(L, sb, e[1]);
      break;
    }
    fmt = e+2;
  }
  addstr(L, sb, fmt, (MSize)strlen(fmt));
  setstrV(L, L->top, lj_str_new(L, sb->buf, sb->n));
  incr_top(L);
  return strVdata(L->top - 1);
}