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crc

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A library used to calculate CRC checksums for binary data.

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crc src crc_16_modbus.c
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src/crc_16_modbus.c 

#include "erl_nif.h"



static const unsigned short modbus_crc[16] = {

  0x0000, 0xcc01, 0xd801, 0x1400,

	0xf001, 0x3c00, 0x2800, 0xe401,

	0xa001, 0x6c00, 0x7800, 0xb401,

	0x5000, 0x9c01, 0x8801, 0x4400

};



unsigned short calc_16_modbus(unsigned char* data, int size) {

  unsigned short result = 0xffff;

  unsigned char val;



  while (size--) {

    val = *data++;



    result = modbus_crc[(val ^ result) & 15] ^ (result >> 4);

    result = modbus_crc[((val >> 4) ^ result) & 15] ^ (result >> 4);

  }



  return result;

}



ERL_NIF_TERM _calc_16_modbus(ErlNifEnv* env, int arc, const ERL_NIF_TERM argv[])

{

  ErlNifBinary binary;

  int data_size = 0;

  unsigned char* data = NULL;

  unsigned short crc = 0xffff;



  if(arc != 1 || !enif_inspect_binary(env, argv[0], &binary)) {

    return enif_make_badarg(env);

  }



  data_size = binary.size;

  data = binary.data;



  crc = calc_16_modbus(data, data_size);



  return enif_make_int(env, crc);

}