mirror of https://github.com/bsnes-emu/bsnes.git
66 lines
1.7 KiB
C++
66 lines
1.7 KiB
C++
#pragma once
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//error detection code
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namespace nall::CD::EDC {
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//polynomial(x) = (x^16 + x^15 + x^2 + 1) * (x^16 + x^2 + x + 1)
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inline auto polynomial(uint8_t x) -> uint32_t {
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static uint32_t lookup[256]{};
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static bool once = false;
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if(!once) { once = true;
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for(uint n : range(256)) {
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uint32_t edc = n;
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for(uint b : range(8)) edc = edc >> 1 ^ (edc & 1 ? 0xd8018001 : 0);
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lookup[n] = edc;
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}
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}
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return lookup[x];
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}
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//
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inline auto create(array_view<uint8_t> input) -> uint32_t {
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uint32_t sum = 0;
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for(auto& byte : input) sum = sum >> 8 ^ polynomial(sum ^ byte);
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return sum;
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}
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inline auto create(array_view<uint8_t> input, array_span<uint8_t> output) -> bool {
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if(output.size() != 4) return false;
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auto sum = create(input);
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output[0] = sum >> 0;
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output[1] = sum >> 8;
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output[2] = sum >> 16;
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output[3] = sum >> 24;
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return true;
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}
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inline auto createMode1(array_span<uint8_t> sector) -> bool {
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if(sector.size() != 2352) return false;
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return create({sector, 2064}, {sector + 2064, 4});
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}
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//
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inline auto verify(array_view<uint8_t> input, uint32_t edc) -> bool {
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return edc == create(input);
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}
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inline auto verify(array_view<uint8_t> input, array_view<uint8_t> compare) -> bool {
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if(compare.size() != 4) return false;
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auto sum = create(input);
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if(compare[0] != uint8_t(sum >> 0)) return false;
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if(compare[1] != uint8_t(sum >> 8)) return false;
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if(compare[2] != uint8_t(sum >> 16)) return false;
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if(compare[3] != uint8_t(sum >> 24)) return false;
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return true;
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}
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inline auto verifyMode1(array_view<uint8_t> sector) -> bool {
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if(sector.size() != 2352) return false;
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return verify({sector, 2064}, {sector + 2064, 4});
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}
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}
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