ptr = s->gb.buffer + (get_bits_count(&s->gb)>>3);
ptr = (uint8_t *)(s->gb.buffer + (get_bits_count(&s->gb)>>3));
static void seek_to_maindata(MPADecodeContext *s, unsigned int backstep){    uint8_t *ptr;    /* compute current position in stream */    ptr = s->gb.buffer + (get_bits_count(&s->gb)>>3);    /* copy old data before current one */    ptr -= backstep;    memcpy(ptr, s->inbuf1[s->inbuf_index ^ 1] +            BACKSTEP_SIZE + s->old_frame_size - backstep, backstep);    /* init get bits again */    init_get_bits(&s->gb, ptr, (s->frame_size + backstep)*8);    /* prepare next buffer */    s->inbuf_index ^= 1;    s->inbuf = &s->inbuf1[s->inbuf_index][BACKSTEP_SIZE];    s->old_frame_size = s->frame_size;}