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// 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 ABSL_STRINGS_INTERNAL_BITS_H_
#define ABSL_STRINGS_INTERNAL_BITS_H_
#include <cstdint>
#if defined(_MSC_VER) && defined(_M_X64)
#include <intrin.h>
#pragma intrinsic(_BitScanReverse64)
#endif
namespace absl {
inline namespace lts_2018_06_20 {
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
} // inline namespace lts_2018_06_20
} // namespace absl
#endif // ABSL_STRINGS_INTERNAL_BITS_H_
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