picolibrary

CRC Facilities

CRC facilities are defined in the include/picolibrary/crc.h/source/picolibrary/crc.cc header/source file pair.

Table of Contents

  1. Calculators
  2. Calculator Utilities

Calculators

The ::picolibrary::CRC::Calculation_Parameters struct captures a CRC calculation’s parameters.

A std::ostream insertion operator is defined for ::picolibrary::CRC::Calculation_Parameters if the PICOLIBRARY_ENABLE_AUTOMATED_TESTING project configuration option is ON. The insertion operator is defined in the include/picolibrary/testing/automated/crc.h/source/picolibrary/testing/automated/crc.cc header/source file pair.

The ::picolibrary::CRC::Calculator_Concept defines the expected interface of a CRC calculator implementation.

Data for creating data driven automated tests for CRC calculator implementations is defined in the include/picolibrary/testing/automated/crc.h/source/picolibrary/testing/automated/crc.cc header/source file pair. The ::picolibrary::Testing::Automated::CRC::Calculator_Test_Case struct is used to store the data for a calculator test case. std::uint8_t register calculator test cases are defined in the ::picolibrary::Testing::Automated::CRC::CALCULATOR_TEST_CASES_8 array. std::uint16_t register calculator test cases are defined in the ::picolibrary::Testing::Automated::CRC::CALCULATOR_TEST_CASES_16 array. std::uint32_t register calculator test cases are defined in the ::picolibrary::Testing::Automated::CRC::CALCULATOR_TEST_CASES_32 array.

picolibrary provides the following CRC calculator implementations:

The ::picolibrary::CRC::Bitwise_Calculator CRC calculator implementation processes messages one bit at a time, and requires a message augment to push the entirety of a message through the calculation. While this results in lower performance than table driven implementations, memory use is lower due to the lack of a lookup table. ::picolibrary::CRC::Bitwise_Calculator automated tests are defined in the test/automated/picolibrary/crc/bitwise_calculator/main.cc source file.

The ::picolibrary::CRC::Augmented_Byte_Indexed_Lookup_Table_Calculator CRC calculator implementation processes messages one byte at a time, and requires a message augment to push the entirety of a message through the calculation. While this results in higher memory use than bitwise implementations and table driven implementations that process messages one nibble at a time, performance is higher due to the message processing loop requiring fewer iterations to process a message. The ::picolibrary::CRC::Direct_Byte_Indexed_Lookup_Table_Calculator CRC calculator implementation is strictly superior to the ::picolibrary::CRC::Augmented_Byte_Indexed_Lookup_Table_Calculator implementation since it does not have to process a message augment in addition to the message itself. ::picolibrary::CRC::Augmented_Byte_Indexed_Lookup_Table_Calculator automated tests are defined in the test/automated/picolibrary/crc/augmented_byte_indexed_lookup_table_calculator/main.cc source file.

The ::picolibrary::CRC::Direct_Byte_Indexed_Lookup_Table_Calculator CRC calculator implementation processes messages one byte at a time, and does not require a message augment to push the entirety of a message through the calculation. While this results in higher memory use than bitwise implementations and table driven implementations that process messages one nibble at a time, performance is higher due to the message processing loop requiring fewer iterations to process a message. ::picolibrary::CRC::Direct_Byte_Indexed_Lookup_Table_Calculator automated tests are defined in the test/automated/picolibrary/crc/direct_byte_indexed_lookup_table_calculator/main.cc source file.

The ::picolibrary::CRC::Augmented_Nibble_Indexed_Lookup_Table_Calculator CRC calculator implementation processes messages one nibble at a time, and requires a message augment to push the entirety of a message through the calculation. This achieves a balance between implementations that are optimized for performance (table driven implementations that process messages one or more bytes at a time), and those that are optimized for memory use (bitwise implementations). The ::picolibrary::CRC::Direct_Nibble_Indexed_Lookup_Table_Calculator CRC calculator implementation is strictly superior to the ::picolibrary::CRC::Augmented_Nibble_Indexed_Lookup_Table_Calculator implementation since it does not have to process a message augment in addition to the message itself. ::picolibrary::CRC::Augmented_Nibble_Indexed_Lookup_Table_Calculator automated tests are defined in the test/automated/picolibrary/crc/augmented_nibble_indexed_lookup_table_calculator/main.cc source file.

The ::picolibrary::CRC::Direct_Nibble_Indexed_Lookup_Table_Calculator CRC calculator implementation processes messages one nibble at a time, and does not require a message augment to push the entirety of a message through the calculation. This achieves a balance between implementations that are optimized for performance (table driven implementations that process messages one or more bytes at a time), and those that are optimized for memory use (bitwise implementations). ::picolibrary::CRC::Direct_Nibble_Indexed_Lookup_Table_Calculator automated tests are defined in the test/automated/picolibrary/crc/direct_nibble_indexed_lookup_table_calculator/main.cc source file.

Automated test fixtures for CRC calculator implementations (::uint8Register, ::uint16Register, and uint32Register) are available if the PICOLIBRARY_ENABLE_AUTOMATED_TESTING project configuration is ON. The automated test fixtures are defined in the include/picolibrary/testing/automated/crc.h/source/picolibrary/testing/automated/crc.cc header/source file pair.

Calculator Utilities

To get the input processor for a CRC calculation, use the ::picolibrary::CRC::input_processor() function.

To get the output processor for a CRC calculation, use the ::picolibrary::CRC::output_processor() function.

To get a message augment array for a CRC calculation, use the ::picolibrary::CRC::Message_Augment type alias.

To generate a byte indexed lookup table for a CRC calculation, use the ::picolibrary::generate_byte_indexed_lookup_table() function.

To get the number of bits in a nibble, use the ::picolibrary::CRC::NIBBLE_DIGITS constant.

To get the largest value a nibble can hold, use the ::picolibrary::CRC::NIBBLE_MAX constant.

To get the pair of nibbles that make up a byte, use the ::picolibrary::get_byte_nibbles() function.

To generate a nibble indexed lookup table for a CRC calculation, use the ::picolibrary::generate_nibble_indexed_lookup_table() function.

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