Class: OpenC3::Crc16

Inherits:
Crc show all
Defined in:
lib/openc3/utilities/crc.rb,
ext/openc3/ext/crc/crc.c

Overview

Calculates 16-bit CRCs over a buffer of data.

Constant Summary collapse

DEFAULT_POLY =

CRC-16-CCITT default polynomial

0x1021
DEFAULT_SEED =

Seed for 16-bit CRC

0xFFFF

Constants inherited from Crc

OpenC3::Crc::BIT_REVERSE_TABLE

Instance Attribute Summary

Attributes inherited from Crc

#poly, #reflect, #seed, #table, #xor

Instance Method Summary collapse

Methods inherited from Crc

#bit_reverse_16, #bit_reverse_32, #bit_reverse_64, #bit_reverse_8

Constructor Details

#initialize(poly = DEFAULT_POLY, seed = DEFAULT_SEED, xor = false, reflect = false) ⇒ Crc16

Creates a 16 bit CRC algorithm instance. By default it is initialzed to use the CRC-16-CCITT algorithm.

Parameters:

  • poly (Integer) (defaults to: DEFAULT_POLY) —

    Polynomial to use when calculating the CRC

  • seed (Integer) (defaults to: DEFAULT_SEED) —

    Seed value to start the calculation

  • xor (Boolean) (defaults to: false) —

    Whether to XOR the CRC result with 0xFFFF

  • reflect (Boolean) (defaults to: false) —

    Whether to bit reverse each byte of data before calculating the CRC



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# File 'lib/openc3/utilities/crc.rb', line 257

def initialize(poly = DEFAULT_POLY,
               seed = DEFAULT_SEED,
               xor  = false,
               reflect = false)
  super(poly, seed, xor, reflect)
end

Instance Method Details

#calc(*args) ⇒ Object Also known as: calculate_crc16

Calculate a 16-bit CRC



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# File 'ext/openc3/ext/crc/crc.c', line 182

static VALUE crc16_calculate(int argc, VALUE *argv, VALUE self)
{
  volatile VALUE param_data = Qnil;
  volatile VALUE param_seed = Qnil;
  unsigned char *data = NULL;
  unsigned short *table = NULL;
  int i = 0;
  long length = 0;
  unsigned short crc = 0;

  switch (argc)
  {
  case 1:
    Check_Type(argv[0], T_STRING);
    param_data = argv[0];
    param_seed = rb_ivar_get(self, id_ivar_seed);
    break;
  case 2:
    Check_Type(argv[0], T_STRING);
    param_data = argv[0];
    if (argv[1] == Qnil)
    {
      param_seed = rb_ivar_get(self, id_ivar_seed);
    }
    else
    {
      param_seed = argv[1];
    }
    break;
  default:
    /* Invalid number of arguments given */
    rb_raise(rb_eArgError, "wrong number of arguments (%d for 1..2)", argc);
    break;
  };

  crc = NUM2UINT(param_seed);
  data = (unsigned char *)RSTRING_PTR(param_data);
  length = RSTRING_LEN(param_data);
  table = (unsigned short *)RSTRING_PTR(rb_ivar_get(self, id_ivar_table));

  if (RTEST(rb_ivar_get(self, id_ivar_reflect)))
  {
    for (i = 0; i < length; i++)
    {
      crc = (crc << 8) ^ table[(crc >> 8) ^ bit_reverse_8(data[i])];
    }

    if (RTEST(rb_ivar_get(self, id_ivar_xor)))
    {
      return UINT2NUM(bit_reverse_16(crc ^ 0xFFFF));
    }
    else
    {
      return UINT2NUM(bit_reverse_16(crc));
    }
  }
  else
  {
    for (i = 0; i < length; i++)
    {
      crc = (crc << 8) ^ table[(crc >> 8) ^ data[i]];
    }

    if (RTEST(rb_ivar_get(self, id_ivar_xor)))
    {
      return UINT2NUM(crc ^ 0xFFFF);
    }
    else
    {
      return UINT2NUM(crc);
    }
  }
}