void OsRetrieveCpuInfo()

in c++/src/CpuInfoUtil.cc [139:209]
54 lines of code
26 McCabe index (conditional complexity)

    void OsRetrieveCpuInfo(int64_t* hardwareFlags, CpuInfo::Vendor* vendor,
                           std::string* modelName) {
      int register_EAX_id = 1;
      int highest_valid_id = 0;
      int highest_extended_valid_id = 0;
      std::bitset<32> features_ECX;
      std::array<int, 4> cpuInfo;

      // Get highest valid id
      __cpuid(cpuInfo.data(), 0);
      highest_valid_id = cpuInfo[0];
      // HEX of "GenuineIntel": 47656E75 696E6549 6E74656C
      // HEX of "AuthenticAMD": 41757468 656E7469 63414D44
      if (cpuInfo[1] == 0x756e6547 && cpuInfo[3] == 0x49656e69 && cpuInfo[2] == 0x6c65746e) {
        *vendor = CpuInfo::Vendor::Intel;
      } else if (cpuInfo[1] == 0x68747541 && cpuInfo[3] == 0x69746e65 && cpuInfo[2] == 0x444d4163) {
        *vendor = CpuInfo::Vendor::AMD;
      }

      if (highest_valid_id <= register_EAX_id) {
        return;
      }

      // EAX=1: Processor Info and Feature Bits
      __cpuidex(cpuInfo.data(), register_EAX_id, 0);
      features_ECX = cpuInfo[2];

      // Get highest extended id
      __cpuid(cpuInfo.data(), 0x80000000);
      highest_extended_valid_id = cpuInfo[0];

      // Retrieve CPU model name
      if (highest_extended_valid_id >= static_cast<int>(0x80000004)) {
        modelName->clear();
        for (int i = 0x80000002; i <= static_cast<int>(0x80000004); ++i) {
          __cpuidex(cpuInfo.data(), i, 0);
          *modelName += std::string(reinterpret_cast<char*>(cpuInfo.data()), sizeof(cpuInfo));
        }
      }

      bool zmm_enabled = false;
      if (features_ECX[27]) {  // OSXSAVE
        // Query if the OS supports saving ZMM registers when switching contexts
        int64_t xcr0 = _xgetbv(0);
        zmm_enabled = (xcr0 & 0xE0) == 0xE0;
      }

      if (features_ECX[9]) *hardwareFlags |= CpuInfo::SSSE3;
      if (features_ECX[19]) *hardwareFlags |= CpuInfo::SSE4_1;
      if (features_ECX[20]) *hardwareFlags |= CpuInfo::SSE4_2;
      if (features_ECX[23]) *hardwareFlags |= CpuInfo::POPCNT;
      if (features_ECX[28]) *hardwareFlags |= CpuInfo::AVX;

      // cpuid with EAX=7, ECX=0: Extended Features
      register_EAX_id = 7;
      if (highest_valid_id > register_EAX_id) {
        __cpuidex(cpuInfo.data(), register_EAX_id, 0);
        std::bitset<32> features_EBX = cpuInfo[1];

        if (features_EBX[3]) *hardwareFlags |= CpuInfo::BMI1;
        if (features_EBX[5]) *hardwareFlags |= CpuInfo::AVX2;
        if (features_EBX[8]) *hardwareFlags |= CpuInfo::BMI2;
        if (zmm_enabled) {
          if (features_EBX[16]) *hardwareFlags |= CpuInfo::AVX512F;
          if (features_EBX[17]) *hardwareFlags |= CpuInfo::AVX512DQ;
          if (features_EBX[28]) *hardwareFlags |= CpuInfo::AVX512CD;
          if (features_EBX[30]) *hardwareFlags |= CpuInfo::AVX512BW;
          if (features_EBX[31]) *hardwareFlags |= CpuInfo::AVX512VL;
        }
      }
    }