51 lines
1.8 KiB
C++
51 lines
1.8 KiB
C++
#include "wrapping_integers.hh"
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// Dummy implementation of a 32-bit wrapping integer
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// For Lab 2, please replace with a real implementation that passes the
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// automated checks run by `make check_lab2`.
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template <typename... Targs>
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void DUMMY_CODE(Targs &&.../* unused */) {}
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using namespace std;
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//! Transform an "absolute" 64-bit sequence number (zero-indexed) into a WrappingInt32
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//! \param n The input absolute 64-bit sequence number
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//! \param isn The initial sequence number
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WrappingInt32 wrap(uint64_t n, WrappingInt32 isn) {
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uint32_t result = static_cast<uint32_t>(n) + isn.raw_value();
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return WrappingInt32{result};
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}
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//! Transform a WrappingInt32 into an "absolute" 64-bit sequence number (zero-indexed)
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//! \param n The relative sequence number
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//! \param isn The initial sequence number
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//! \param checkpoint A recent absolute 64-bit sequence number
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//! \returns the 64-bit sequence number that wraps to `n` and is closest to `checkpoint`
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//!
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//! \note Each of the two streams of the TCP connection has its own ISN. One stream
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//! runs from the local TCPSender to the remote TCPReceiver and has one ISN,
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//! and the other stream runs from the remote TCPSender to the local TCPReceiver and
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//! has a different ISN.
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#define MODULO (1UL << 32)
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uint64_t unwrap(WrappingInt32 n, WrappingInt32 isn, uint64_t checkpoint) {
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// well, really ulgy impl
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// have to make sure that no overflow happens
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uint64_t tmp = static_cast<uint64_t>(n.raw_value() - isn.raw_value());
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tmp += (checkpoint >> 32) << 32;
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if (tmp > checkpoint) {
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if (tmp < MODULO || tmp - checkpoint < checkpoint - (tmp - MODULO)) {
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return tmp;
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} else {
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return tmp - MODULO;
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}
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} else {
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if (checkpoint - tmp < tmp + MODULO - checkpoint) {
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return tmp;
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} else {
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return tmp + MODULO;
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}
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}
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}
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