--- /dev/null
+// 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
+//
+// https://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_BASE_INTERNAL_BITS_H_
+#define ABSL_BASE_INTERNAL_BITS_H_
+
+// This file contains bitwise ops which are implementation details of various
+// absl libraries.
+
+#include <cstdint>
+
+// Clang on Windows has __builtin_clzll; otherwise we need to use the
+// windows intrinsic functions.
+#if defined(_MSC_VER)
+#include <intrin.h>
+#if defined(_M_X64)
+#pragma intrinsic(_BitScanReverse64)
+#pragma intrinsic(_BitScanForward64)
+#endif
+#pragma intrinsic(_BitScanReverse)
+#pragma intrinsic(_BitScanForward)
+#endif
+
+#include "absl/base/attributes.h"
+
+#if defined(_MSC_VER)
+// We can achieve something similar to attribute((always_inline)) with MSVC by
+// using the __forceinline keyword, however this is not perfect. MSVC is
+// much less aggressive about inlining, and even with the __forceinline keyword.
+#define ABSL_BASE_INTERNAL_FORCEINLINE __forceinline
+#else
+// Use default attribute inline.
+#define ABSL_BASE_INTERNAL_FORCEINLINE inline ABSL_ATTRIBUTE_ALWAYS_INLINE
+#endif
+
+
+namespace absl {
+namespace base_internal {
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros64Slow(uint64_t n) {
+ 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"[n] + zeroes;
+}
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros64(uint64_t n) {
+#if defined(_MSC_VER) && defined(_M_X64)
+ // MSVC does not have __buitin_clzll. Use _BitScanReverse64.
+ unsigned long result = 0; // NOLINT(runtime/int)
+ if (_BitScanReverse64(&result, n)) {
+ return 63 - result;
+ }
+ return 64;
+#elif defined(_MSC_VER)
+ // MSVC does not have __buitin_clzll. Compose two calls to _BitScanReverse
+ unsigned long result = 0; // NOLINT(runtime/int)
+ if ((n >> 32) && _BitScanReverse(&result, n >> 32)) {
+ return 31 - result;
+ }
+ if (_BitScanReverse(&result, n)) {
+ return 63 - result;
+ }
+ return 64;
+#elif defined(__GNUC__)
+ // Use __builtin_clzll, which uses the following instructions:
+ // x86: bsr
+ // ARM64: clz
+ // PPC: cntlzd
+ static_assert(sizeof(unsigned long long) == sizeof(n), // NOLINT(runtime/int)
+ "__builtin_clzll does not take 64-bit arg");
+
+ // Handle 0 as a special case because __builtin_clzll(0) is undefined.
+ if (n == 0) {
+ return 64;
+ }
+ return __builtin_clzll(n);
+#else
+ return CountLeadingZeros64Slow(n);
+#endif
+}
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros32Slow(uint64_t n) {
+ int zeroes = 28;
+ 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"[n] + zeroes;
+}
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros32(uint32_t n) {
+#if defined(_MSC_VER)
+ unsigned long result = 0; // NOLINT(runtime/int)
+ if (_BitScanReverse(&result, n)) {
+ return 31 - result;
+ }
+ return 32;
+#elif defined(__GNUC__)
+ // Use __builtin_clz, which uses the following instructions:
+ // x86: bsr
+ // ARM64: clz
+ // PPC: cntlzd
+ static_assert(sizeof(int) == sizeof(n),
+ "__builtin_clz does not take 32-bit arg");
+
+ // Handle 0 as a special case because __builtin_clz(0) is undefined.
+ if (n == 0) {
+ return 32;
+ }
+ return __builtin_clz(n);
+#else
+ return CountLeadingZeros32Slow(n);
+#endif
+}
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero64Slow(uint64_t n) {
+ int c = 63;
+ n &= ~n + 1;
+ if (n & 0x00000000FFFFFFFF) c -= 32;
+ if (n & 0x0000FFFF0000FFFF) c -= 16;
+ if (n & 0x00FF00FF00FF00FF) c -= 8;
+ if (n & 0x0F0F0F0F0F0F0F0F) c -= 4;
+ if (n & 0x3333333333333333) c -= 2;
+ if (n & 0x5555555555555555) c -= 1;
+ return c;
+}
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero64(uint64_t n) {
+#if defined(_MSC_VER) && defined(_M_X64)
+ unsigned long result = 0; // NOLINT(runtime/int)
+ _BitScanForward64(&result, n);
+ return result;
+#elif defined(_MSC_VER)
+ unsigned long result = 0; // NOLINT(runtime/int)
+ if (static_cast<uint32_t>(n) == 0) {
+ _BitScanForward(&result, n >> 32);
+ return result + 32;
+ }
+ _BitScanForward(&result, n);
+ return result;
+#elif defined(__GNUC__)
+ static_assert(sizeof(unsigned long long) == sizeof(n), // NOLINT(runtime/int)
+ "__builtin_ctzll does not take 64-bit arg");
+ return __builtin_ctzll(n);
+#else
+ return CountTrailingZerosNonZero64Slow(n);
+#endif
+}
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero32Slow(uint32_t n) {
+ int c = 31;
+ n &= ~n + 1;
+ if (n & 0x0000FFFF) c -= 16;
+ if (n & 0x00FF00FF) c -= 8;
+ if (n & 0x0F0F0F0F) c -= 4;
+ if (n & 0x33333333) c -= 2;
+ if (n & 0x55555555) c -= 1;
+ return c;
+}
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero32(uint32_t n) {
+#if defined(_MSC_VER)
+ unsigned long result = 0; // NOLINT(runtime/int)
+ _BitScanForward(&result, n);
+ return result;
+#elif defined(__GNUC__)
+ static_assert(sizeof(int) == sizeof(n),
+ "__builtin_ctz does not take 32-bit arg");
+ return __builtin_ctz(n);
+#else
+ return CountTrailingZerosNonZero32Slow(n);
+#endif
+}
+
+#undef ABSL_BASE_INTERNAL_FORCEINLINE
+
+} // namespace base_internal
+} // namespace absl
+
+#endif // ABSL_BASE_INTERNAL_BITS_H_
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