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Merge pull request #91 from TomHarte/TableCRC

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Switches to a table-based implementation of CRC generation
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Thomas Harte 2016-12-31 14:16:17 -05:00 committed by GitHub
commit 4c62487e6e
1 changed files with 17 additions and 10 deletions
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27
NumberTheory/CRC.hpp
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@ -16,23 +16,30 @@ namespace NumberTheory {
class CRC16 { class CRC16 {
public: public:
CRC16(uint16_t polynomial, uint16_t reset_value) : CRC16(uint16_t polynomial, uint16_t reset_value) :
reset_value_(reset_value), value_(reset_value), polynomial_(polynomial) {} reset_value_(reset_value), value_(reset_value)
{
for(int c = 0; c < 256; c++)
{
uint16_t shift_value = (uint16_t)(c << 8);
for(int b = 0; b < 8; b++)
{
uint16_t exclusive_or = (shift_value&0x8000) ? polynomial : 0x0000;
shift_value = (uint16_t)(shift_value << 1) ^ exclusive_or;
}
xor_table[c] = (uint16_t)shift_value;
}
}
inline void reset() { value_ = reset_value_; } inline void reset() { value_ = reset_value_; }
inline void add(uint8_t value) { inline void add(uint8_t byte) {
// TODO: go table based value_ = (uint16_t)((value_ << 8) ^ xor_table[(value_ >> 8) ^ byte]);
value_ ^= (uint16_t)value << 8;
for(int c = 0; c < 8; c++)
{
uint16_t exclusive_or = (value_&0x8000) ? polynomial_ : 0x0000;
value_ = (uint16_t)(value_ << 1) ^ exclusive_or;
}
} }
inline uint16_t get_value() const { return value_; } inline uint16_t get_value() const { return value_; }
inline void set_value(uint16_t value) { value_ = value; } inline void set_value(uint16_t value) { value_ = value; }
private: private:
const uint16_t reset_value_, polynomial_; const uint16_t reset_value_;
uint16_t xor_table[256];
uint16_t value_; uint16_t value_;
}; };