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// Most significant bit first (big-endian) // x^16+x^12+x^5+1 = (1) 0001 0000 0010 0001 = 0x1021 function crc(byte array string[1..len], int len) { rem := 0 // A popular variant complements rem here for i from 1 to len { rem := rem xor (string[i] leftShift (n-8)) // n = 16 in this example for j from 1 to 8 { // Assuming 8 bits per byte if rem and 0x8000 { // if leftmost (most significant) bit is set rem := (rem leftShift 1) xor 0x1021 } else { rem := rem leftShift 1 } rem := rem and 0xffff // Trim remainder to 16 bits } } // A popular variant complements rem here return rem }Je to CRC-16. Řekněme, že chcu počítat CRC-4, budu si předpočítávat tabulku, takže pro každý byte si spočítám element:
// pro každý 8b byte "nějakejByte" byte rem := 0 xor (nějakejByte leftShift (4-8)) for j from 1 to 8 { // if rem and 0x8 { rem := (rem leftShift 1) xor poly } else { rem := rem leftShift 1 } rem := rem and 0x7 } tabulka[nějakejByte] := remVyjde mi tam posun vlevo o -4 (4-8) ??? To se mi nezdá.
Řešení dotazu:
module jardik.checksum.crc; import jardik.inttypes; import std.traits; public struct CRCIntTraits(const size_t _CRC_BITS, _IntType = UIntFast!(_CRC_BITS)) { static const size_t CRC_BITS = _CRC_BITS; alias IntType = _IntType; static assert(isIntegral!(IntType), "Integral type required"); static assert(IntType.sizeof * 8 >= CRC_BITS, "Integral doesn't have enough bits"); static const IntType ZERO = 0; static const IntType ONE = 1; static const IntType CRC_HIBIT = ONE << (CRC_BITS-1); static if (CRC_BITS < IntType.sizeof * 8) { static const IntType CRC_MASK = ~cast(IntType)(~ZERO << CRC_BITS); static pure IntType crcMask(IntType val) { return val & CRC_MASK; } } else { static const IntType CRC_MASK = ~ZERO; static pure IntType crcMask(IntType val) { return val; } } } private pure IntType reflect(const size_t NUM_BITS, IntType) (IntType value) { alias IntTraits = CRCIntTraits!(NUM_BITS, IntType); IntType result = IntTraits.ZERO; for (size_t i = 0; i < NUM_BITS; ++i) { if (value & IntTraits.ONE) { result |= (IntTraits.ONE << (NUM_BITS - 1 - i)); } value >>= 1; } return result; } public struct CRCPoly(const size_t _CRC_BITS) { static const size_t CRC_BITS = _CRC_BITS; alias IntTraits = CRCIntTraits!(CRC_BITS); alias IntType = IntTraits.IntType; IntType normalValue; IntType reflectedValue; static CRCPoly fromData(U)(in U[] polyData) { IntType value = IntTraits.ZERO; foreach(n; polyData) { assert(n < CRC_BITS); value |= IntTraits.ONE << n; } return normal(value); } static CRCPoly normal(IntType value) { return CRCPoly(value, reflect!(CRC_BITS)(value)); } static CRCPoly reflected(IntType value) { return CRCPoly(reflect!(CRC_BITS)(value), value); } } unittest { import std.stdio; import core.exception; printf(">> Testing CRC poly generator\n"); // CRC-4-ITU try { immutable ubyte[] crc4polyData = [0,1]; const uint crc4polyCheck = 0x3U; const uint crc4polyReflectedCheck = 0xCU; auto crc4poly = CRCPoly!(4).fromData(crc4polyData).normalValue; auto crc4polyReflected = CRCPoly!(4).fromData(crc4polyData).reflectedValue; assert(crc4poly == crc4polyCheck); assert(crc4polyReflected == crc4polyReflectedCheck); printf(" ... CRC-4 poly passed.\n"); } catch (AssertError) { printf(" ... CRC-4 poly failed.\n"); } // CRC-32 try { immutable ubyte[] crc32polyData = [0,1,2,4,5,7,8,10,11,12,16,22,23,26]; const uint crc32polyCheck = 0x04C11DB7U; const uint crc32polyReflectedCheck = 0xEDB88320U; auto crc32poly = CRCPoly!(32).fromData(crc32polyData).normalValue; auto crc32polyReflected = CRCPoly!(32).fromData(crc32polyData).reflectedValue; assert(crc32poly == crc32polyCheck); assert(crc32polyReflected == crc32polyReflectedCheck); printf(" ... CRC-32 poly passed.\n"); } catch (AssertError) { printf(" ... CRC-32 poly failed.\n"); } // CRC-64-ECMA try { immutable ubyte[] crc64polyData = [ 0,1,4,7,9,10,12,13,17,19,21,22,23,24,27,29,31, 32,33,35,37,38,39,40,45,46,47,52,53,54,55,57,62 ]; const ulong crc64polyCheck = 0x42F0E1EBA9EA3693UL; const ulong crc64polyReflectedCheck = 0xC96C5795D7870F42UL; auto crc64poly = CRCPoly!(64).fromData(crc64polyData).normalValue; auto crc64polyReflected = CRCPoly!(64).fromData(crc64polyData).reflectedValue; assert(crc64poly == crc64polyCheck); assert(crc64polyReflected == crc64polyReflectedCheck); printf(" ... CRC-64 poly passed.\n"); } catch (AssertError) { printf(" ... CRC-64 poly failed.\n"); } } public class CRCTableGen(// number of CRC bits const size_t _CRC_BITS, // integer type backing the CRC table entry _IntType = UIntFast!(_CRC_BITS), // whether to reflect CRC table entries const bool REFLECT = false) { enum : size_t { CRC_BITS = _CRC_BITS } alias IntType = _IntType; alias IntTraits = CRCIntTraits!(CRC_BITS, IntType); alias FastIntType = UIntFast!(CRC_BITS); alias FastIntTraits = CRCIntTraits!(CRC_BITS, FastIntType); public static pure IntType[] generate(in CRCPoly!CRC_BITS poly) { IntType[] table = new IntType[256]; generateImpl(table, poly); return table; } public static pure IntType[] generate(IntType[] reuseTable, in CRCPoly!CRC_BITS poly) { IntType[] table = reuseTable.length < 256 ? new IntType[256] : reuseTable; generateImpl(table, poly); return table; } static if (!REFLECT) { private static pure void generateImpl(IntType[] table, in CRCPoly!CRC_BITS poly) { FastIntType remainder; FastIntType polyVal = poly.normalValue; for (size_t divident = 0; divident < 256; ++divident) { remainder = FastIntTraits.ZERO; for (size_t mask = 0x80; mask != 0; mask >>= 1) { if (divident & mask) remainder ^= FastIntTraits.CRC_HIBIT; if (remainder & FastIntTraits.CRC_HIBIT) { remainder <<= 1; remainder ^= polyVal; } else { remainder <<= 1; } } table[divident] = cast(IntType)FastIntTraits.crcMask(remainder); } } } else { private static pure void generateImpl(IntType[] table, in CRCPoly!CRC_BITS poly) { FastIntType rem; FastIntType polyVal = poly.reflectedValue; size_t k; for (size_t divident = 0; divident < 256; ++divident) { rem = cast(FastIntType)divident; for (k = 0; k < 8; ++k) rem = rem & 1 ? polyVal ^ (rem >> 1) : (rem >> 1); table[divident] = cast(IntType)FastIntTraits.crcMask(rem); } } } } unittest { import std.stdio; import core.exception; const auto poly = CRCPoly!(32)(0x04C11DB7U, 0xEDB88320U); uint[] crcTable = CRCTableGen!(32, uint, false).generate(poly); uint[] crcTableReflected = CRCTableGen!(32, uint, true).generate(poly); File f = File("crc32test.txt", "w"); f.writeln(" NORMAL | REFLECT "); f.writeln("---------|----------"); for (size_t i = 0; i < 256; ++i) { f.writefln("%08X | %08X", crcTable[i], crcTableReflected[i]); } auto crc4poly = CRCPoly!(4).normal(0b1011U); ubyte[] crc4table = CRCTableGen!(4, ubyte, false).generate(crc4poly); f = File("crc4test.txt", "w"); size_t i; for (i = 0; i < 256-8; i+=8) { f.writefln("0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X,", crc4table[i], crc4table[i+1], crc4table[i+2], crc4table[i+3], crc4table[i+4], crc4table[i+5], crc4table[i+6], crc4table[i+7]); } f.writefln("0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X, 0x%02X", crc4table[i], crc4table[i+1], crc4table[i+2], crc4table[i+3], crc4table[i+4], crc4table[i+5], crc4table[i+6], crc4table[i+7]); } public class CRC(const size_t CRC_BITS, _TableIntType = FastInt!(CRC_BITS), const bool _REFLECT_DATA = false, const bool _REFLECT_REM = _REFLECT_DATA) { alias IntTraits = CRCIntTraits!(CRC_BITS); alias IntType = IntTraits.IntType; alias TableIntType = _TableIntType; alias TableGen = CRCTableGen!(CRC_BITS, TableIntType, _REFLECT_DATA); alias PolyType = CRCPoly!(CRC_BITS); const(TableIntType)[] m_table; IntType m_init; IntType m_xor; IntType m_val; public this(in PolyType poly, IntType initVal, IntType xorVal) { this(TableGen.generate(poly), initVal, xorVal); } public this(const(TableIntType)[] table, IntType initVal, IntType xorVal) { m_table = table; m_init = initVal; m_xor = xorVal; m_val = m_init; } public void reset() { m_val = m_init; } public void update(string str) { update(cast(const(ubyte[]))str); } static if (_REFLECT_DATA) { public void update(in ubyte[] buf) { size_t tableIndex; foreach (IntType b; buf) { tableIndex = cast(size_t)((m_val ^ b) & cast(IntType)0xFFU); m_val = cast(IntType)(m_table[tableIndex] ^ (m_val >> 8)); } } } else { public void update(in ubyte[] buf) { size_t tableIndex; foreach (IntType b; buf) { static if (CRC_BITS < 8) tableIndex = cast(size_t)(b ^ (m_val << (8 - CRC_BITS))); else tableIndex = cast(size_t)(b ^ (m_val >> (CRC_BITS - 8))); m_val = IntTraits.crcMask(cast(IntType)(m_table[tableIndex] ^ (m_val << 8))); } } } public IntType peek() const { static if (_REFLECT_REM == _REFLECT_DATA) { return IntTraits.crcMask(m_val ^ m_xor); } else { return IntTraits.crcMask(reflect!(CRC_BITS, IntType)(m_val) ^ m_xor); } } public IntType finish() { IntType crcVal = peek(); reset(); return crcVal; } } public class CRC32 : CRC!(32, uint, true, true) { public this() { //super(PolyType.normal(0x04C11DB7U), 0xFFFFFFFFU, 0xFFFFFFFFU); super(PolyType.reflected(0xEDB88320U), 0xFFFFFFFFU, 0xFFFFFFFFU); } public this(const(uint)[] table) { super(table, 0xFFFFFFFFU, 0xFFFFFFFFU); } } unittest { import std.stdio; import core.exception; printf(">> Testing CRC32\n"); try { CRC32 crc32 = new CRC32(); crc32.update("abc"); ulong crc = crc32.finish(); assert(crc == 0x352441C2U); printf(" ... passed.\n"); } catch (AssertError) { printf(" ... failed.\n"); } printf(">> Testing CRC4 poly = 0xB\n"); try { auto crc4 = new CRC!(4, ushort, false, false)(CRCPoly!(4).normal(0xB), 0, 0); crc4.update("abcdef"); assert(crc4.finish() == 0x2); printf(" ... passed.\n"); } catch (AssertError) { printf(" ... failed.\n"); } printf(">> Testing CRC4 poly = 0xB, reflected\n"); try { auto crc4 = new CRC!(4, ushort, true, true)(CRCPoly!(4).normal(0xB), 0, 0); crc4.update("abcdef"); assert(crc4.finish() == 0x8); printf(" ... passed.\n"); } catch (AssertError) { printf(" ... failed.\n"); } printf(">> Testing CRC16-CCITT\n"); try { auto poly = CRCPoly!(16).normal(0x1021); auto crc16ccitt = new CRC!(16, ushort, false, false)(poly, 0xffff, 0); crc16ccitt.update("abcdef"); assert(crc16ccitt.finish() == 0x34ED); printf(" ... passed.\n"); } catch (AssertError) { printf(" ... failed.\n"); } printf(">> Testing CRC16\n"); try { auto poly = CRCPoly!(16).normal(0x8005); auto crc16 = new CRC!(16, ushort, true, true)(poly, 0, 0); crc16.update("abcdef"); assert(crc16.finish() == 0x5805); printf(" ... passed.\n"); } catch (AssertError) { printf(" ... failed.\n"); } printf(">> Testing CRC-12\n"); try { auto poly = CRCPoly!(12).normal(0x80F); auto crc = new CRC!(12, ushort, false, false)(poly, 0, 0); crc.update("abcdef"); assert(crc.finish() == 0x6C7); printf(" ... passed.\n"); } catch (AssertError) { printf(" ... failed.\n"); } printf(">> Testing CRC-12 reflected\n"); try { auto poly = CRCPoly!(12).normal(0x80F); auto crc = new CRC!(12, ushort, true, true)(poly, 0, 0); crc.update("abcdef"); assert(crc.finish() == 0xFE6); printf(" ... passed.\n"); } catch (AssertError) { printf(" ... failed.\n"); } } int main() { return 0; }
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