text: // Copyright 2018 The Abseil Authors.
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //      http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  #ifndef S2_THIRD_PARTY_ABSL_STRINGS_INTERNAL_BITS_H_
  #define S2_THIRD_PARTY_ABSL_STRINGS_INTERNAL_BITS_H_
  
  #include <cstdint>
  
  #if defined(_MSC_VER) && defined(_M_X64)
  #include <intrin.h>
  #pragma intrinsic(_BitScanReverse64)
  #endif
  
  namespace s2_absl {
  namespace strings_internal {
  
  // Returns the number of leading 0 bits in a 64-bit value.
  inline int CountLeadingZeros64(uint64_t n) {
  #if defined(__GNUC__)
    static_assert(sizeof(unsigned long long) == sizeof(n),  // NOLINT(runtime/int)
                  "__builtin_clzll does not take 64bit arg");
    return n == 0 ? 64 : __builtin_clzll(n);
  #elif defined(_MSC_VER) && defined(_M_X64)
    unsigned long result;  // NOLINT(runtime/int)
    if (_BitScanReverse64(&result, n)) {
      return 63 - result;
    }
    return 64;
  #else
    int zeroes = 60;
    if (n >> 32) zeroes -= 32, n >>= 32;
    if (n >> 16) zeroes -= 16, n >>= 16;
    if (n >> 8) zeroes -= 8, n >>= 8;
    if (n >> 4) zeroes -= 4, n >>= 4;
    return "\4\3\2\2\1\1\1\1\0\0\0\0\0\0\0\0"[n] + zeroes;
  #endif
  }
  
  }  // namespace strings_internal
  }  // namespace s2_absl
  
  #endif  // S2_THIRD_PARTY_ABSL_STRINGS_INTERNAL_BITS_H_
  