A benchmark comparing bytewise and bitwise CRC implementations

crc_benchmark.cpp

#include <benchmark/benchmark.h>
#include <cstdint>
#include <array>
#include <random>
#include <algorithm>

static std::array<std::uint8_t, (1 << 16)> data;

static unsigned int CRC16_bitwise(const uint8_t *buf, int len)
{  
  unsigned int crc = 0xFFFF;
  for (int pos = 0; pos < len; pos++)
  {
  crc ^= (unsigned int)buf[pos];    // XOR byte into least sig. byte of crc

  for (int i = 8; i != 0; i--) {    // Loop over each bit
    if ((crc & 0x0001) != 0) {      // If the LSB is set
      crc >>= 1;                    // Shift right and XOR 0xA001
      crc ^= 0xA001;
    }
    else                            // Else LSB is not set
      crc >>= 1;                    // Just shift right
    }
  }

  return crc;
}

static uint16_t CRC16_bytewise (const uint8_t *nData, int wLength)
{
    static const uint16_t wCRCTable[] = {
    0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
    0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
    0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
    0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
    0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
    0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
    0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
    0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
    0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
    0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
    0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
    0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
    0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
    0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
    0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
    0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
    0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
    0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
    0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
    0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
    0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
    0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
    0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
    0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
    0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
    0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
    0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
    0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
    0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
    0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
    0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
    0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040 };

    uint8_t nTemp;
    uint16_t wCRCWord = 0xFFFF;

    while (wLength--)
    {
        nTemp = *nData++ ^ wCRCWord;
        wCRCWord >>= 8;
        wCRCWord  ^= wCRCTable[(nTemp & 0xFF)];
    }
    return wCRCWord;
} // End: CRC16

static void BM_BitwiseCRC(benchmark::State& state) {
  for (auto _ : state)
    benchmark::DoNotOptimize(CRC16_bitwise(data.data(), state.range(0)));
  
  state.SetBytesProcessed(state.iterations() * state.range(0));
}
BENCHMARK(BM_BitwiseCRC)->RangeMultiplier(2)->Range(8, 1<<16);

static void BM_BytewiseCRC(benchmark::State& state) {
  for (auto _ : state)
    benchmark::DoNotOptimize(CRC16_bytewise(data.data(), state.range(0)));
  
  state.SetBytesProcessed(state.iterations() * state.range(0));
}
BENCHMARK(BM_BytewiseCRC)->RangeMultiplier(2)->Range(8, 1<<16);

int main(int argc, char** argv) {
  std::random_device r;
  std::default_random_engine e1(r());
  std::uniform_int_distribution<uint8_t> uniform_dist(0, 0xFF);
  std::generate(std::begin(data), std::end(data), [&]() {
    return uniform_dist(e1);
  });

  benchmark::Initialize(&argc, argv);
  benchmark::RunSpecifiedBenchmarks();
}

/* Results on a i7-2630QM :
-------------------------------------------------------------------------------
Benchmark                     Time             CPU   Iterations UserCounters...
-------------------------------------------------------------------------------
BM_BitwiseCRC/8             133 ns          132 ns      5381388 bytes_per_second=57.6174M/s
BM_BitwiseCRC/16            268 ns          268 ns      2609578 bytes_per_second=56.89M/s
BM_BitwiseCRC/32            538 ns          538 ns      1291759 bytes_per_second=56.7167M/s
BM_BitwiseCRC/64           1078 ns         1078 ns       634390 bytes_per_second=56.6419M/s
BM_BitwiseCRC/128          2143 ns         2141 ns       327213 bytes_per_second=57.0035M/s
BM_BitwiseCRC/256          4280 ns         4276 ns       162734 bytes_per_second=57.1019M/s
BM_BitwiseCRC/512          8569 ns         8563 ns        81169 bytes_per_second=57.0248M/s
BM_BitwiseCRC/1024        17145 ns        17132 ns        40801 bytes_per_second=57.0007M/s
BM_BitwiseCRC/2048        34240 ns        34168 ns        20202 bytes_per_second=57.1624M/s
BM_BitwiseCRC/4096        68297 ns        68250 ns        10147 bytes_per_second=57.2348M/s
BM_BitwiseCRC/8192       137088 ns       137001 ns         5103 bytes_per_second=57.025M/s
BM_BitwiseCRC/16384      275114 ns       274899 ns         2558 bytes_per_second=56.839M/s
BM_BitwiseCRC/32768      548467 ns       547900 ns         1254 bytes_per_second=57.0359M/s
BM_BitwiseCRC/65536     1098852 ns      1098000 ns          637 bytes_per_second=56.9217M/s
BM_BytewiseCRC/8           14.6 ns         14.5 ns     49068842 bytes_per_second=524.685M/s
BM_BytewiseCRC/16          35.3 ns         35.2 ns     19844193 bytes_per_second=433.19M/s
BM_BytewiseCRC/32          86.3 ns         86.3 ns      8097436 bytes_per_second=353.816M/s
BM_BytewiseCRC/64           192 ns          192 ns      3610579 bytes_per_second=317.391M/s
BM_BytewiseCRC/128          397 ns          397 ns      1747146 bytes_per_second=307.44M/s
BM_BytewiseCRC/256          808 ns          807 ns       859120 bytes_per_second=302.531M/s
BM_BytewiseCRC/512         1628 ns         1627 ns       426534 bytes_per_second=300.076M/s
BM_BytewiseCRC/1024        3292 ns         3289 ns       214352 bytes_per_second=296.951M/s
BM_BytewiseCRC/2048        6548 ns         6544 ns       105093 bytes_per_second=298.481M/s
BM_BytewiseCRC/4096       13125 ns        13116 ns        53236 bytes_per_second=297.823M/s
BM_BytewiseCRC/8192       26390 ns        26349 ns        26357 bytes_per_second=296.505M/s
BM_BytewiseCRC/16384      53102 ns        53041 ns        13195 bytes_per_second=294.583M/s
BM_BytewiseCRC/32768     104876 ns       104795 ns         6552 bytes_per_second=298.2M/s
BM_BytewiseCRC/65536     213223 ns       213057 ns         3342 bytes_per_second=293.349M/s
*/