Not really. The line is this: long adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale) - (tp->rcv_adv - tp->rcv_nxt);

So it's really: long = uint(long, (long)uint32) - (uint32-uint32)

Here's the problem on x64: you're converting a 64-bit long to a uint, then doing a subtraction with another uint, then placing that result into a 64-bit long. Since the compiler is just doing an assignment rather than a sign extension, which is why there is a large positive number rather than -1.

Changing it to use the lmin macro would make it: long = long(long, (long)uint32) - (uint32-uint32)

This still has the underlying issue(using 32-bit values in 64-bit buckets), which should work out fine, but may have issues down the road.

It makes more sense to change all the long types to int32/uint32 types rather than just cast longs everywhere. If recwin and adv were changed to int32, it would be: int32 = uint32(int32, uint32) - (uint32 - uint32)

While this potentially has issues if the uints are between 0x80000000 and 0xfffffff, it's a safer solution than using longs.

EDIT: added some explanation