jbig2_table_read_bits(const byte *data, size_t *bitoffset, const int bitlen)
{
    uint32_t result = 0;
    uint32_t byte_offset = *bitoffset / 8;
    const int endbit = (*bitoffset & 7) + bitlen;
    const int n_proc_bytes = (endbit + 7) / 8;
    const int rshift = n_proc_bytes * 8 - endbit;
    int i;

    for (i = n_proc_bytes - 1; i >= 0; i--) {
        uint32_t d = data[byte_offset++];
        const int nshift = i * 8 - rshift;

        if (nshift > 0)
            d <<= nshift;
        else if (nshift < 0)
            d >>= -nshift;
        result |= d;
    }
    result &= ~(-1 << bitlen);
    *bitoffset += bitlen;
    return result;
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.