04dd99d8c1
- 2201f1644336e64280dbd20207d8fbc3bfea2bf4 Internal change. by Abseil Team <absl-team@google.com> - 94e6b5b20d2cc754c99a18c575a4f1f3cd1f28d4 Rename no_throw_ctor to nothrow_ctor to match the standar... by Abseil Team <absl-team@google.com> - 86aa34d2129c4914c5133b7b619480aae786288e Update header files in debugging target by Tom Manshreck <shreck@google.com> - ed234519ced458724a7267b8fdf184eaae1c97c7 Remove CMAKE_CXX_WARNING_VLA from our c++ flags in the cm... by Jon Cohen <cohenjon@google.com> GitOrigin-RevId: abe587c2360b21f085b7d65a77d840015bc04cf6 Change-Id: I92f9301c69419d3830c358b88984967185aa33f6
53 lines
1.6 KiB
C++
53 lines
1.6 KiB
C++
// Copyright 2018 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef ABSL_STRINGS_INTERNAL_BITS_H_
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#define ABSL_STRINGS_INTERNAL_BITS_H_
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#include <cstdint>
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#if defined(_MSC_VER) && defined(_M_X64)
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#include <intrin.h>
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#pragma intrinsic(_BitScanReverse64)
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#endif
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namespace absl {
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namespace strings_internal {
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// Returns the number of leading 0 bits in a 64-bit value.
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inline int CountLeadingZeros64(uint64_t n) {
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#if defined(__GNUC__)
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static_assert(sizeof(unsigned long long) == sizeof(n), // NOLINT(runtime/int)
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"__builtin_clzll does not take 64bit arg");
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return n == 0 ? 64 : __builtin_clzll(n);
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#elif defined(_MSC_VER) && defined(_M_X64)
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unsigned long result; // NOLINT(runtime/int)
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if (_BitScanReverse64(&result, n)) {
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return 63 - result;
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}
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return 64;
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#else
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int zeroes = 60;
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if (n >> 32) zeroes -= 32, n >>= 32;
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if (n >> 16) zeroes -= 16, n >>= 16;
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if (n >> 8) zeroes -= 8, n >>= 8;
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if (n >> 4) zeroes -= 4, n >>= 4;
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return "\4\3\2\2\1\1\1\1\0\0\0\0\0\0\0\0"[n] + zeroes;
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#endif
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}
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} // namespace strings_internal
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} // namespace absl
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#endif // ABSL_STRINGS_INTERNAL_BITS_H_
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