/*
 * This is a constexpr-capable CRC32 checksum based on Ivor Wanders' code from
 * https://gist.github.com/iwanders/8e1cb7b92af2ccf8d1a73450d771f483
 *
 * which was, in turn:
 *
 * Based on code from Python's crcmod module. Polynomial "crc-32".
 * polynomial: 0x104C11DB7, bit reverse algorithm:
 * crcmod.Crc(0x104C11DB7, initCrc=0, xorOut=0xFFFFFFFF)
 *
 * I made it possible to do
 *
 * std::string a_string("abc");
 * uint32_t string_crc = morph::crc32 (a_string);
 *
 * or:
 *
 * constexpr uint32_t crc = morph::crc32 (a_string);
 *
 * and we can use it in a switch statement like:
 *
 *   using std::literals::string_view_literals::operator""sv;
 *
 *   switch (string_crc) {
 *   case morph::crc32 ("abc"sv):
 *   {
 *       std::cout << "Matched abc" << std::endl;
 *       break;
 *   }
 *   // etc
 *   }
 */

/*
  The MIT License (MIT)
  Copyright (c) 2018 Ivor Wanders
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  SOFTWARE.
*/

#pragma once

#include <cstdint>
#include <type_traits>
#include <string_view>

namespace morph {

    static constexpr uint32_t crc_table[256] =
    {
        0x00000000u, 0x77073096u, 0xee0e612cu, 0x990951bau, 0x076dc419u,
        0x706af48fu, 0xe963a535u, 0x9e6495a3u, 0x0edb8832u, 0x79dcb8a4u,
        0xe0d5e91eu, 0x97d2d988u, 0x09b64c2bu, 0x7eb17cbdu, 0xe7b82d07u,
        0x90bf1d91u, 0x1db71064u, 0x6ab020f2u, 0xf3b97148u, 0x84be41deu,
        0x1adad47du, 0x6ddde4ebu, 0xf4d4b551u, 0x83d385c7u, 0x136c9856u,
        0x646ba8c0u, 0xfd62f97au, 0x8a65c9ecu, 0x14015c4fu, 0x63066cd9u,
        0xfa0f3d63u, 0x8d080df5u, 0x3b6e20c8u, 0x4c69105eu, 0xd56041e4u,
        0xa2677172u, 0x3c03e4d1u, 0x4b04d447u, 0xd20d85fdu, 0xa50ab56bu,
        0x35b5a8fau, 0x42b2986cu, 0xdbbbc9d6u, 0xacbcf940u, 0x32d86ce3u,
        0x45df5c75u, 0xdcd60dcfu, 0xabd13d59u, 0x26d930acu, 0x51de003au,
        0xc8d75180u, 0xbfd06116u, 0x21b4f4b5u, 0x56b3c423u, 0xcfba9599u,
        0xb8bda50fu, 0x2802b89eu, 0x5f058808u, 0xc60cd9b2u, 0xb10be924u,
        0x2f6f7c87u, 0x58684c11u, 0xc1611dabu, 0xb6662d3du, 0x76dc4190u,
        0x01db7106u, 0x98d220bcu, 0xefd5102au, 0x71b18589u, 0x06b6b51fu,
        0x9fbfe4a5u, 0xe8b8d433u, 0x7807c9a2u, 0x0f00f934u, 0x9609a88eu,
        0xe10e9818u, 0x7f6a0dbbu, 0x086d3d2du, 0x91646c97u, 0xe6635c01u,
        0x6b6b51f4u, 0x1c6c6162u, 0x856530d8u, 0xf262004eu, 0x6c0695edu,
        0x1b01a57bu, 0x8208f4c1u, 0xf50fc457u, 0x65b0d9c6u, 0x12b7e950u,
        0x8bbeb8eau, 0xfcb9887cu, 0x62dd1ddfu, 0x15da2d49u, 0x8cd37cf3u,
        0xfbd44c65u, 0x4db26158u, 0x3ab551ceu, 0xa3bc0074u, 0xd4bb30e2u,
        0x4adfa541u, 0x3dd895d7u, 0xa4d1c46du, 0xd3d6f4fbu, 0x4369e96au,
        0x346ed9fcu, 0xad678846u, 0xda60b8d0u, 0x44042d73u, 0x33031de5u,
        0xaa0a4c5fu, 0xdd0d7cc9u, 0x5005713cu, 0x270241aau, 0xbe0b1010u,
        0xc90c2086u, 0x5768b525u, 0x206f85b3u, 0xb966d409u, 0xce61e49fu,
        0x5edef90eu, 0x29d9c998u, 0xb0d09822u, 0xc7d7a8b4u, 0x59b33d17u,
        0x2eb40d81u, 0xb7bd5c3bu, 0xc0ba6cadu, 0xedb88320u, 0x9abfb3b6u,
        0x03b6e20cu, 0x74b1d29au, 0xead54739u, 0x9dd277afu, 0x04db2615u,
        0x73dc1683u, 0xe3630b12u, 0x94643b84u, 0x0d6d6a3eu, 0x7a6a5aa8u,
        0xe40ecf0bu, 0x9309ff9du, 0x0a00ae27u, 0x7d079eb1u, 0xf00f9344u,
        0x8708a3d2u, 0x1e01f268u, 0x6906c2feu, 0xf762575du, 0x806567cbu,
        0x196c3671u, 0x6e6b06e7u, 0xfed41b76u, 0x89d32be0u, 0x10da7a5au,
        0x67dd4accu, 0xf9b9df6fu, 0x8ebeeff9u, 0x17b7be43u, 0x60b08ed5u,
        0xd6d6a3e8u, 0xa1d1937eu, 0x38d8c2c4u, 0x4fdff252u, 0xd1bb67f1u,
        0xa6bc5767u, 0x3fb506ddu, 0x48b2364bu, 0xd80d2bdau, 0xaf0a1b4cu,
        0x36034af6u, 0x41047a60u, 0xdf60efc3u, 0xa867df55u, 0x316e8eefu,
        0x4669be79u, 0xcb61b38cu, 0xbc66831au, 0x256fd2a0u, 0x5268e236u,
        0xcc0c7795u, 0xbb0b4703u, 0x220216b9u, 0x5505262fu, 0xc5ba3bbeu,
        0xb2bd0b28u, 0x2bb45a92u, 0x5cb36a04u, 0xc2d7ffa7u, 0xb5d0cf31u,
        0x2cd99e8bu, 0x5bdeae1du, 0x9b64c2b0u, 0xec63f226u, 0x756aa39cu,
        0x026d930au, 0x9c0906a9u, 0xeb0e363fu, 0x72076785u, 0x05005713u,
        0x95bf4a82u, 0xe2b87a14u, 0x7bb12baeu, 0x0cb61b38u, 0x92d28e9bu,
        0xe5d5be0du, 0x7cdcefb7u, 0x0bdbdf21u, 0x86d3d2d4u, 0xf1d4e242u,
        0x68ddb3f8u, 0x1fda836eu, 0x81be16cdu, 0xf6b9265bu, 0x6fb077e1u,
        0x18b74777u, 0x88085ae6u, 0xff0f6a70u, 0x66063bcau, 0x11010b5cu,
        0x8f659effu, 0xf862ae69u, 0x616bffd3u, 0x166ccf45u, 0xa00ae278u,
        0xd70dd2eeu, 0x4e048354u, 0x3903b3c2u, 0xa7672661u, 0xd06016f7u,
        0x4969474du, 0x3e6e77dbu, 0xaed16a4au, 0xd9d65adcu, 0x40df0b66u,
        0x37d83bf0u, 0xa9bcae53u, 0xdebb9ec5u, 0x47b2cf7fu, 0x30b5ffe9u,
        0xbdbdf21cu, 0xcabac28au, 0x53b39330u, 0x24b4a3a6u, 0xbad03605u,
        0xcdd70693u, 0x54de5729u, 0x23d967bfu, 0xb3667a2eu, 0xc4614ab8u,
        0x5d681b02u, 0x2a6f2b94u, 0xb40bbe37u, 0xc30c8ea1u, 0x5a05df1bu,
        0x2d02ef8du
    };

    constexpr uint32_t crc32 (const std::string_view& str)
    {
        const char* data = str.data();
        uint32_t len = str.size();
        uint32_t crc = 0;

        crc = crc ^ 0xffffffffu;
        for (uint32_t i = 0; i < len; i++) {
            crc = crc_table[*data ^ (crc & 0xff)] ^ (crc >> 8);
            data++;
        }
        crc = crc ^ 0xffffffffu;
        return crc;
    }

}  // namespace morph
