CRC-32C

crc32c.h

#pragma once

#include <cstdint>

#include <x86intrin.h>

inline
std::uint32_t crc32c(const void * input, std::size_t size, std::uint32_t result = ~0)
{
    auto i8 = static_cast< const std::uint8_t * >(input);
    auto count = std::min(size, (sizeof(std::uint32_t) - ((i8 - static_cast< decltype(i8) >(0)) % sizeof(std::uint32_t))) % sizeof(std::uint32_t));
    for (std::size_t p = 0; p < count; ++p) {
        result = _mm_crc32_u8(result, i8[p]);
    }
    i8 += count;
    size -= count;
    auto i32 = static_cast< const std::uint32_t * >(static_cast< const void * >(i8));
    for (std::size_t p = 0; p < size / sizeof(std::uint32_t); ++p) {
        result = _mm_crc32_u32(result, i32[p]);
    }
    i8 += size;
    size %= sizeof(std::uint32_t);
    i8 -= size;
    for (std::size_t p = 0; p < size; ++p) {
        result = _mm_crc32_u8(result, i8[p]);
    }
    return ~result; // crc32c({0xAB, 0x9B, 0xE0, 0x9B}) == 0, crc32c("DYB|O") == 0
}