hs_ucs2_2_utf8
static int32_t hs_ucs2_2_utf8(uint16_t c_16, uint8_t *s_8);
amt = hs_ucs2_2_utf8(c, (uint8_t *)&to[len]);
amt = hs_ucs2_2_utf8(c, (uint8_t *)to);