90 lines
2.0 KiB
C++
90 lines
2.0 KiB
C++
#ifndef CHAOS_PADDING_PADDERISO7816_HPP
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#define CHAOS_PADDING_PADDERISO7816_HPP
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#include <cstddef>
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#include <cstdint>
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#include <limits>
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#include "Padding/Padder.hpp"
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#include "Service/Branchless.hpp"
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#include "Service/ChaosException.hpp"
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namespace Chaos::Padding
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{
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class PadderIso7816
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{
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public:
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template<typename OutputIt>
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static void Pad(OutputIt begin, OutputIt end)
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{
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OutputIt it = begin;
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if (it != end)
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{
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*it++ = static_cast<uint8_t>(0x80);
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for (; it != end; ++it)
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{
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*it = 0;
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}
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}
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else
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{
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throw Service::ChaosException("PadderIso7816::Pad(): invalid range");
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}
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}
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struct ComputeUnpadResult
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{
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bool IsOkay_;
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uint8_t PadSize_;
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};
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template<typename InputIt>
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static ComputeUnpadResult ComputeUnpad(InputIt begin, InputIt end) noexcept
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{
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if (begin == end)
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{
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return { .IsOkay_ = false, .PadSize_ = 0 };
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}
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uint8_t padSizeIncrement = 1;
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uint8_t padSize = 0;
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uint8_t encountered0x80 = Branchless::FalseMask;
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uint8_t onlyZerosPast0x80 = Branchless::TrueMask;
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InputIt it = end;
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while (it != begin && padSize < std::numeric_limits<uint8_t>::max())
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{
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--it;
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const uint8_t byte = *it;
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padSizeIncrement = Branchless::Sel<uint8_t>(encountered0x80, 0, 1);
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encountered0x80 |= Branchless::Eq<uint8_t, uint8_t>(byte, 0x80);
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onlyZerosPast0x80 &= Branchless::IsZero<uint8_t, uint8_t>(byte) | encountered0x80;
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padSize += padSizeIncrement;
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}
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uint8_t isOkay = encountered0x80 & onlyZerosPast0x80;
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return
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{
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.IsOkay_ = Branchless::ToBool(isOkay),
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.PadSize_ = Branchless::Sel<uint8_t>(isOkay, padSize, 0)
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};
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}
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private:
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using Branchless = Service::Branchless;
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};
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static_assert(Padder<PadderIso7816>);
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} // namespace Chaos::Padding
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#endif // CHAOS_PADDING_PADDERISO7816_HPP
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