Module: TDriver::NativeExtensions::CRC

Defined in:

ext/native_extensions.c

Class Method Summary

• .crc16_ibm(*args) ⇒ Object

Class Method Details

.crc16_ibm(*args) ⇒ Object

# File 'ext/native_extensions.c', line 157

static VALUE crc16_ibm( int argc, VALUE* argv, VALUE self ) { 

/*

  # IBM-CRC-16: fallback when native extensions are not supported (e.g. jruby)
  def crc16_ibm( buf, crc = 0xffff )

    buf.each_byte do | c |

      crc = ( ( crc >> 4 ) & 0x0fff ) ^ @IBM_16[ ( ( crc ^ c ) & 15 ) ]

      crc = ( ( crc >> 4 ) & 0x0fff ) ^ @IBM_16[ ( ( crc ^ ( c >> 4 ) ) & 15 ) ]

    end

    # result
    ~crc & 0xffff

  end # crc16_ibm

*/

  // variables for arguments
  VALUE string, initial_crc;

  // retrieve arguments
  rb_scan_args(argc, argv, "11", &string, &initial_crc);

  unsigned int crc = 0xffff; 
  
  if (!NIL_P(initial_crc)){

    // verify initial crc value
    Check_Type( initial_crc, T_FIXNUM );
  
    crc = FIX2INT( initial_crc );
  
  }
  
  // verify argument type
  Check_Type( string, T_STRING );

  const unsigned char* data = RSTRING_PTR( string );
  
  unsigned int len = RSTRING_LEN( string );
  
  unsigned char c = 0;

  while( len-- ){

    c = *data++;

    crc = ( crc >> 4 ) ^ CRC_16[ ( crc ^ c ) & 15 ];
              
    crc = ( crc >> 4 ) ^ CRC_16[ ( crc ^ ( c >> 4 ) ) & 15 ];

  }

	return INT2FIX( ~crc & 0xffff );


}