ashleyroll / crc_cpp Goto Github PK

Modify the traits to support different bit sizes to allow users to trade space for speed.

First of all, I went to your talk (virtually) at cppcon and I really enjoyed it and this library is really great. I have many legacy IOT message formats that use really "unique" polynomials and starting values, so often it is a real pain to use other libraries. Yours was very easy to specialize for our CRCs.

The issue I am running into is that I can't use the crc class in a constant expression. This seems to be a simple oversight, since to fix it I just mark all the functions in that class constexpr. I can also see how it was missed because all my code worked until this morning! I have no idea what changed, I just renamed some files, but now it won't compile unless I make those functions contexpr.

Here is a minimal example godbolt:

#include <https://raw.githubusercontent.com/AshleyRoll/crc_cpp/main/include/crc_cpp.h>
#include <span>

constexpr bool check_message(std::span<const uint8_t> data, const uint8_t expected) {
    // CRC for upper half is header + first 4 sats and is in byte 14
    crc_cpp::crc8 crc;
    for(const auto b : data) {
        crc.update(b);
    }
    return expected == crc.final();
}

compiler output:

<source>: In function 'constexpr bool check_message(std::span<const unsigned char>, uint8_t)':
<source>:10:33: error: call to non-'constexpr' function 'crc_cpp::impl::crc<TAlgorithm, TABLE_SIZE>::accumulator_type crc_cpp::impl::crc<TAlgorithm, TABLE_SIZE>::final() [with TAlgorithm = crc_cpp::impl::crc_algorithm<unsigned char, 7, 0, 0, false>; crc_cpp::table_size TABLE_SIZE = crc_cpp::table_size::small; crc_cpp::impl::crc<TAlgorithm, TABLE_SIZE>::accumulator_type = unsigned char]'
https://raw.githubusercontent.com/AshleyRoll/crc_cpp/main/include/crc_cpp.h:410:44: note: 'crc_cpp::impl::crc<TAlgorithm, TABLE_SIZE>::accumulator_type crc_cpp::impl::crc<TAlgorithm, TABLE_SIZE>::final() [with TAlgorithm = crc_cpp::impl::crc_algorithm<unsigned char, 7, 0, 0, false>; crc_cpp::table_size TABLE_SIZE = crc_cpp::table_size::small; crc_cpp::impl::crc<TAlgorithm, TABLE_SIZE>::accumulator_type = unsigned char]' declared here
Compiler returned: 1

Add include guards into the header file.

Create a new release and update the Conan package with a new release after the CMake changes from PR #18