Thanks, I worked it.

A 64 bit number which when you look at the low 32 bits is positive is shifted 8 bits right differently in 64 bit world to the same 32 bits in 32 bit land i.e., 0xffffffff01111111 in 64 bit land is shifted 8 bits right and shifts ff into the lower 32 bits whereas 0x11111111 shifted right in 32 bit land has 00 shifted into the left.

I managed to keep the original code with use integer and perl's >> by adding

            my $to_shift = $crc;
            if (($crc & 0x80000000) != 0) {
                $to_shift |= 0xffffffff00000000;
            } else {
                $to_shift &= 0x00000000ffffffff;
            }
            $to_shift = $to_shift >> 8;
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