Problem while calculating checksum: casting int into signed int32

Question

I need to convert the following c code (to calculate the checksum for a file) to python. I wrote the appropriate code in python, but the result did not match c version. The problem was that python automatically advances int to infinity when an overflow occurs, and this leads to incorrect checksums.

Any ideas how to overcome this problem? or is there a python function that takes a long time to convert to a signed int32?

thank

int calcChecksum(const guchar *data, gsize len)
{ 

    const guchar *p = data;
    int checksum = 0, g, i = len;

    while(i--) {
            checksum = (checksum << 4) + *p++;

            if((g = (checksum & 0xf0000000)) != 0)
                    checksum ^= g >> 23;

            checksum &= ~g;
    }
    return checksum;
}

Decision:

Thanks for the help. Here is the function that worked for me -

 def int32(x):
    x = 0xffffffff & x
    if x > 0x7fffffff :
        return - ( ~(x - 1) & 0xffffffff )
    else : return x 

Answer 1

numpy.int32 numpy.uint32, . 1 << 32 , "".