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https://github.com/portapack-mayhem/mayhem-firmware.git
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Totoo
61 lines
1.2 KiB
C++
61 lines
1.2 KiB
C++
#include "tetra_descrambler.hpp"
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namespace ui::external_app::tetra_rx {
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static inline uint8_t lfsr_step(uint32_t& s) {
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uint8_t b = 0;
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b ^= (s >> (32 - 32)) & 1;
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b ^= (s >> (32 - 26)) & 1;
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b ^= (s >> (32 - 23)) & 1;
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b ^= (s >> (32 - 22)) & 1;
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b ^= (s >> (32 - 16)) & 1;
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b ^= (s >> (32 - 12)) & 1;
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b ^= (s >> (32 - 11)) & 1;
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b ^= (s >> (32 - 10)) & 1;
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b ^= (s >> (32 - 8)) & 1;
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b ^= (s >> (32 - 7)) & 1;
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b ^= (s >> (32 - 5)) & 1;
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b ^= (s >> (32 - 4)) & 1;
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b ^= (s >> (32 - 2)) & 1;
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b ^= (s >> (32 - 1)) & 1;
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s = (s >> 1) | (uint32_t(b) << 31);
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return b;
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}
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void Descrambler::generate(
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uint32_t init,
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uint8_t* seq,
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size_t bits) {
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uint32_t s = init;
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for (size_t i = 0; i < bits; i++)
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seq[i] = lfsr_step(s);
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}
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void Descrambler::descramble(
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BitVector& bits,
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uint32_t init) {
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uint32_t s = init;
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for (size_t i = 0; i < bits.size(); i++)
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bits.xor_bit(i, lfsr_step(s));
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}
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uint32_t Descrambler::dmo_scramb_init(
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uint32_t mni,
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uint32_t src) {
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uint32_t init =
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(src & 0xFFFFFF) |
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((mni & 0x3F) << 24);
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init <<= 2;
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init |= 3;
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return init;
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}
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} // namespace ui::external_app::tetra_rx
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