c->bytestream_end= buf + buf_size;
void ff_init_cabac_decoder(CABACContext *c, const uint8_t *buf, int buf_size){    c->bytestream_start=     c->bytestream= buf;    c->low= *c->bytestream++;    c->low= (c->low<<9) + ((*c->bytestream++)<<1);    c->range= 0x1FE00;    c->bits_left= 7;}