| 1 | #ifdef __cplusplus |
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| 2 | extern "C" { |
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| 3 | #endif |
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| 4 | |
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| 5 | #ifndef _CHECKSUM_H_ |
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| 6 | #define _CHECKSUM_H_ |
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| 7 | |
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| 8 | // Visual Studio versions before 2010 don't have stdint.h, so we just error out. |
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| 9 | #if (defined _MSC_VER) && (_MSC_VER < 1600) |
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| 10 | #error "The C-MAVLink implementation requires Visual Studio 2010 or greater" |
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| 11 | #endif |
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| 12 | |
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| 13 | #include <stdint.h> |
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| 14 | |
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| 15 | /** |
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| 16 | * |
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| 17 | * CALCULATE THE CHECKSUM |
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| 18 | * |
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| 19 | */ |
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| 20 | |
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| 21 | #define X25_INIT_CRC 0xffff |
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| 22 | #define X25_VALIDATE_CRC 0xf0b8 |
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| 23 | |
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| 24 | #ifndef HAVE_CRC_ACCUMULATE |
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| 25 | /** |
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| 26 | * @brief Accumulate the X.25 CRC by adding one char at a time. |
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| 27 | * |
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| 28 | * The checksum function adds the hash of one char at a time to the |
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| 29 | * 16 bit checksum (uint16_t). |
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| 30 | * |
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| 31 | * @param data new char to hash |
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| 32 | * @param crcAccum the already accumulated checksum |
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| 33 | **/ |
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| 34 | static inline void crc_accumulate(uint8_t data, uint16_t *crcAccum) |
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| 35 | { |
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| 36 | /*Accumulate one byte of data into the CRC*/ |
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| 37 | uint8_t tmp; |
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| 38 | |
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| 39 | tmp = data ^ (uint8_t)(*crcAccum &0xff); |
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| 40 | tmp ^= (tmp<<4); |
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| 41 | *crcAccum = (*crcAccum>>8) ^ (tmp<<8) ^ (tmp <<3) ^ (tmp>>4); |
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| 42 | } |
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| 43 | #endif |
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| 44 | |
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| 45 | |
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| 46 | /** |
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| 47 | * @brief Initiliaze the buffer for the X.25 CRC |
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| 48 | * |
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| 49 | * @param crcAccum the 16 bit X.25 CRC |
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| 50 | */ |
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| 51 | static inline void crc_init(uint16_t* crcAccum) |
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| 52 | { |
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| 53 | *crcAccum = X25_INIT_CRC; |
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| 54 | } |
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| 55 | |
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| 56 | |
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| 57 | /** |
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| 58 | * @brief Calculates the X.25 checksum on a byte buffer |
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| 59 | * |
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| 60 | * @param pBuffer buffer containing the byte array to hash |
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| 61 | * @param length length of the byte array |
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| 62 | * @return the checksum over the buffer bytes |
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| 63 | **/ |
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| 64 | static inline uint16_t crc_calculate(const uint8_t* pBuffer, uint16_t length) |
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| 65 | { |
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| 66 | uint16_t crcTmp; |
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| 67 | crc_init(&crcTmp); |
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| 68 | while (length--) { |
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| 69 | crc_accumulate(*pBuffer++, &crcTmp); |
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| 70 | } |
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| 71 | return crcTmp; |
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| 72 | } |
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| 73 | |
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| 74 | |
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| 75 | /** |
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| 76 | * @brief Accumulate the X.25 CRC by adding an array of bytes |
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| 77 | * |
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| 78 | * The checksum function adds the hash of one char at a time to the |
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| 79 | * 16 bit checksum (uint16_t). |
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| 80 | * |
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| 81 | * @param data new bytes to hash |
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| 82 | * @param crcAccum the already accumulated checksum |
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| 83 | **/ |
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| 84 | static inline void crc_accumulate_buffer(uint16_t *crcAccum, const char *pBuffer, uint16_t length) |
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| 85 | { |
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| 86 | const uint8_t *p = (const uint8_t *)pBuffer; |
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| 87 | while (length--) { |
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| 88 | crc_accumulate(*p++, crcAccum); |
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| 89 | } |
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| 90 | } |
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| 91 | |
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| 92 | #endif /* _CHECKSUM_H_ */ |
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| 93 | |
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| 94 | #ifdef __cplusplus |
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| 95 | } |
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| 96 | #endif |
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