> .. even with a self-compiled 1.2.3, INT_MAX/1000 ... nothing.
> The problem is not crc32(), but the buffer itself:
> 
>    if (pbuf.len > 1024*5) {
>         unsigned char *buf = pbuf.buf;
>         Py_ssize_t len = pbuf.len;
>         Py_ssize_t i;
> fprintf(stderr, "CRC 32 2.1\n");
> for(i=0; (size_t)i < (size_t)len;++i)
>     *buf++ = 1;
> fprintf(stderr, "CRC 32 2.2\n");

Thank you! So it's perhaps a bug in mmap on Snow Leopard.
Could you try to debug a bit more precisely and see at which buffer
offset (from the start) the fault occurs?