bits.c

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#include <libk/bits.h>
 
uint8_t read_byte(bitstream_t* bs) {
 
    size_t byte_pos = bs->bit_pos / 8;
    if (byte_pos > bs->size)
        return 0;
 
    uint8_t val = bs->data[byte_pos];
    if (val == 0xFF) {
        if (byte_pos + 1 < bs->size && bs->data[byte_pos + 1] == 0x00) {
            // Stuffed byte, skip 0x00
            bs->bit_pos += 16;
            return 0xFF;
        } else {
            // Marker encountered, stop reading
            // throw std::runtime_error("JPEG marker encountered in bitstream");
        }
    } else {
        bs->bit_pos += 8;
        return val;
    }
    return 0;
}
 
uint32_t read_bits(bitstream_t* bs, int n) {
    uint32_t val = 0;
    for (int i = 0; i < n; i++) {
        size_t byte_pos = bs->bit_pos / 8;
        int bit_offset = 7 - (bs->bit_pos % 8);
 
        if (byte_pos >= bs->size)
            return val; // EOF
 
        uint8_t byte = read_byte(bs);
        val = (val << 1) | ((byte >> bit_offset) & 1);
    }
    return val;
}
 
uint8_t read_bit(bitstream_t* bs) {
    uint64_t byte_pos = bs->bit_pos / 8;
    uint8_t bit_in_byte = 7 - (bs->bit_pos % 8);
    uint8_t b = (bs->data[byte_pos] >> bit_in_byte) & 1;
    bs->bit_pos++;
    return b;
}