mask.hpp

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#ifndef CCSDS124_MASK_HPP
#define CCSDS124_MASK_HPP
 
#include "bitvector.hpp"
#include "config.hpp"
#include "error.hpp"
 
namespace ccsds124 {
 
template <std::size_t N>
void update_build(BitVector<N>& build, const BitVector<N>& input, const BitVector<N>& prev_input,
                  bool new_mask_flag, std::size_t t) noexcept {
    if (t == 0 || new_mask_flag) {
        // Case 1: t=0 or new_mask_flag set -> reset build to 0
        build.zero();
    } else {
        // Case 2: Normal operation (t > 0 and new_mask_flag = 0)
        // B_t = (I_t XOR I_{t-1}) OR B_{t-1}
        // Optimized: compute in-place without temporary allocation
        for (std::size_t w = 0; w < BitVector<N>::NUM_WORDS; ++w) {
            build.data()[w] |= (input.data()[w] ^ prev_input.data()[w]);
        }
    }
}
 
template <std::size_t N>
void update_mask(BitVector<N>& mask, const BitVector<N>& input, const BitVector<N>& prev_input,
                 const BitVector<N>& build_prev, bool new_mask_flag) noexcept {
    // Optimized: compute in-place without temporary allocation
    if (new_mask_flag) {
        // Case 1: new_mask_flag set -> M_t = (I_t XOR I_{t-1}) OR B_{t-1}
        for (std::size_t w = 0; w < BitVector<N>::NUM_WORDS; ++w) {
            mask.data()[w] = (input.data()[w] ^ prev_input.data()[w]) | build_prev.data()[w];
        }
    } else {
        // Case 2: Normal operation -> M_t = (I_t XOR I_{t-1}) OR M_{t-1}
        for (std::size_t w = 0; w < BitVector<N>::NUM_WORDS; ++w) {
            mask.data()[w] |= (input.data()[w] ^ prev_input.data()[w]);
        }
    }
}
 
template <std::size_t N>
void compute_change(BitVector<N>& change, const BitVector<N>& mask, const BitVector<N>& prev_mask,
                    std::size_t t) noexcept {
    if (t == 0) {
        // CCSDS Eq. 8: D_0 = 0 — no change at initialization; both encoder
        // and decoder start from the same user-specified M_0
        change.zero();
    } else {
        // D_t = M_t XOR M_{t-1}
        change.xor_with(mask, prev_mask);
    }
}
 
} // namespace ccsds124
 
#endif // CCSDS124_MASK_HPP