+/*
+ * Copyright 2017 Facebook, Inc.
+ *
+ * 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.
+ */
+
+/**
+ * Various low-level, bit-manipulation routines.
+ *
+ * findFirstSet(x) [constexpr]
+ * find first (least significant) bit set in a value of an integral type,
+ * 1-based (like ffs()). 0 = no bits are set (x == 0)
+ *
+ * findLastSet(x) [constexpr]
+ * find last (most significant) bit set in a value of an integral type,
+ * 1-based. 0 = no bits are set (x == 0)
+ * for x != 0, findLastSet(x) == 1 + floor(log2(x))
+ *
+ * nextPowTwo(x) [constexpr]
+ * Finds the next power of two >= x.
+ *
+ * isPowTwo(x) [constexpr]
+ * return true iff x is a power of two
+ *
+ * popcount(x)
+ * return the number of 1 bits in x
+ *
+ * Endian
+ * convert between native, big, and little endian representation
+ * Endian::big(x) big <-> native
+ * Endian::little(x) little <-> native
+ * Endian::swap(x) big <-> little
+ *
+ * @author Tudor Bosman (tudorb@fb.com)
+ */
+
+#pragma once
+
+// MSVC does not support intrinsics constexpr
+#if defined(_MSC_VER)
+#define FOLLY_INTRINSIC_CONSTEXPR const
+#else
+#define FOLLY_INTRINSIC_CONSTEXPR constexpr
+#endif
+
+#include <cassert>
+#include <cinttypes>
+#include <cstdint>
+#include <cstring>
+#include <limits>
+#include <type_traits>
+
+#include <folly/Portability.h>
+#include <folly/lang/Assume.h>
+#include <folly/portability/Builtins.h>
+
+namespace folly {
+
+// Generate overloads for findFirstSet as wrappers around
+// appropriate ffs, ffsl, ffsll gcc builtins
+template <class T>
+inline FOLLY_INTRINSIC_CONSTEXPR
+typename std::enable_if<
+ (std::is_integral<T>::value &&
+ std::is_unsigned<T>::value &&
+ sizeof(T) <= sizeof(unsigned int)),
+ unsigned int>::type
+ findFirstSet(T x) {
+ return static_cast<unsigned int>(__builtin_ffs(static_cast<int>(x)));
+}
+
+template <class T>
+inline FOLLY_INTRINSIC_CONSTEXPR
+typename std::enable_if<
+ (std::is_integral<T>::value &&
+ std::is_unsigned<T>::value &&
+ sizeof(T) > sizeof(unsigned int) &&
+ sizeof(T) <= sizeof(unsigned long)),
+ unsigned int>::type
+ findFirstSet(T x) {
+ return static_cast<unsigned int>(__builtin_ffsl(static_cast<long>(x)));
+}
+
+template <class T>
+inline FOLLY_INTRINSIC_CONSTEXPR
+typename std::enable_if<
+ (std::is_integral<T>::value &&
+ std::is_unsigned<T>::value &&
+ sizeof(T) > sizeof(unsigned long) &&
+ sizeof(T) <= sizeof(unsigned long long)),
+ unsigned int>::type
+ findFirstSet(T x) {
+ return static_cast<unsigned int>(__builtin_ffsll(static_cast<long long>(x)));
+}
+
+template <class T>
+inline FOLLY_INTRINSIC_CONSTEXPR
+typename std::enable_if<
+ (std::is_integral<T>::value && std::is_signed<T>::value),
+ unsigned int>::type
+ findFirstSet(T x) {
+ // Note that conversion from a signed type to the corresponding unsigned
+ // type is technically implementation-defined, but will likely work
+ // on any impementation that uses two's complement.
+ return findFirstSet(static_cast<typename std::make_unsigned<T>::type>(x));
+}
+
+// findLastSet: return the 1-based index of the highest bit set
+// for x > 0, findLastSet(x) == 1 + floor(log2(x))
+template <class T>
+inline FOLLY_INTRINSIC_CONSTEXPR
+typename std::enable_if<
+ (std::is_integral<T>::value &&
+ std::is_unsigned<T>::value &&
+ sizeof(T) <= sizeof(unsigned int)),
+ unsigned int>::type
+ findLastSet(T x) {
+ // If X is a power of two X - Y = ((X - 1) ^ Y) + 1. Doing this transformation
+ // allows GCC to remove its own xor that it adds to implement clz using bsr
+ return x ? ((8 * sizeof(unsigned int) - 1) ^ __builtin_clz(x)) + 1 : 0;
+}
+
+template <class T>
+inline FOLLY_INTRINSIC_CONSTEXPR
+typename std::enable_if<
+ (std::is_integral<T>::value &&
+ std::is_unsigned<T>::value &&
+ sizeof(T) > sizeof(unsigned int) &&
+ sizeof(T) <= sizeof(unsigned long)),
+ unsigned int>::type
+ findLastSet(T x) {
+ return x ? ((8 * sizeof(unsigned long) - 1) ^ __builtin_clzl(x)) + 1 : 0;
+}
+
+template <class T>
+inline FOLLY_INTRINSIC_CONSTEXPR
+typename std::enable_if<
+ (std::is_integral<T>::value &&
+ std::is_unsigned<T>::value &&
+ sizeof(T) > sizeof(unsigned long) &&
+ sizeof(T) <= sizeof(unsigned long long)),
+ unsigned int>::type
+ findLastSet(T x) {
+ return x ? ((8 * sizeof(unsigned long long) - 1) ^ __builtin_clzll(x)) + 1
+ : 0;
+}
+
+template <class T>
+inline FOLLY_INTRINSIC_CONSTEXPR
+typename std::enable_if<
+ (std::is_integral<T>::value &&
+ std::is_signed<T>::value),
+ unsigned int>::type
+ findLastSet(T x) {
+ return findLastSet(static_cast<typename std::make_unsigned<T>::type>(x));
+}
+
+template <class T>
+inline FOLLY_INTRINSIC_CONSTEXPR
+typename std::enable_if<
+ std::is_integral<T>::value && std::is_unsigned<T>::value,
+ T>::type
+nextPowTwo(T v) {
+ return v ? (T(1) << findLastSet(v - 1)) : 1;
+}
+
+template <class T>
+inline FOLLY_INTRINSIC_CONSTEXPR typename std::
+ enable_if<std::is_integral<T>::value && std::is_unsigned<T>::value, T>::type
+ prevPowTwo(T v) {
+ return v ? (T(1) << (findLastSet(v) - 1)) : 0;
+}
+
+template <class T>
+inline constexpr typename std::enable_if<
+ std::is_integral<T>::value && std::is_unsigned<T>::value,
+ bool>::type
+isPowTwo(T v) {
+ return (v != 0) && !(v & (v - 1));
+}
+
+/**
+ * Population count
+ */
+template <class T>
+inline typename std::enable_if<
+ (std::is_integral<T>::value &&
+ std::is_unsigned<T>::value &&
+ sizeof(T) <= sizeof(unsigned int)),
+ size_t>::type
+ popcount(T x) {
+ return size_t(__builtin_popcount(x));
+}
+
+template <class T>
+inline typename std::enable_if<
+ (std::is_integral<T>::value &&
+ std::is_unsigned<T>::value &&
+ sizeof(T) > sizeof(unsigned int) &&
+ sizeof(T) <= sizeof(unsigned long long)),
+ size_t>::type
+ popcount(T x) {
+ return size_t(__builtin_popcountll(x));
+}
+
+/**
+ * Endianness detection and manipulation primitives.
+ */
+namespace detail {
+
+template <size_t Size>
+struct uint_types_by_size;
+
+#define FB_GEN(sz, fn) \
+ static inline uint##sz##_t byteswap_gen(uint##sz##_t v) { \
+ return fn(v); \
+ } \
+ template <> \
+ struct uint_types_by_size<sz / 8> { \
+ using type = uint##sz##_t; \
+ };
+
+FB_GEN(8, uint8_t)
+#ifdef _MSC_VER
+FB_GEN(64, _byteswap_uint64)
+FB_GEN(32, _byteswap_ulong)
+FB_GEN(16, _byteswap_ushort)
+#else
+FB_GEN(64, __builtin_bswap64)
+FB_GEN(32, __builtin_bswap32)
+FB_GEN(16, __builtin_bswap16)
+#endif
+
+#undef FB_GEN
+
+template <class T>
+struct EndianInt {
+ static_assert(
+ (std::is_integral<T>::value && !std::is_same<T, bool>::value) ||
+ std::is_floating_point<T>::value,
+ "template type parameter must be non-bool integral or floating point");
+ static T swap(T x) {
+ // we implement this with memcpy because that is defined behavior in C++
+ // we rely on compilers to optimize away the memcpy calls
+ constexpr auto s = sizeof(T);
+ using B = typename uint_types_by_size<s>::type;
+ B b;
+ std::memcpy(&b, &x, s);
+ b = byteswap_gen(b);
+ std::memcpy(&x, &b, s);
+ return x;
+ }
+ static T big(T x) {
+ return kIsLittleEndian ? EndianInt::swap(x) : x;
+ }
+ static T little(T x) {
+ return kIsBigEndian ? EndianInt::swap(x) : x;
+ }
+};
+
+} // namespace detail
+
+// big* convert between native and big-endian representations
+// little* convert between native and little-endian representations
+// swap* convert between big-endian and little-endian representations
+//
+// ntohs, htons == big16
+// ntohl, htonl == big32
+#define FB_GEN1(fn, t, sz) \
+ static t fn##sz(t x) { return fn<t>(x); } \
+
+#define FB_GEN2(t, sz) \
+ FB_GEN1(swap, t, sz) \
+ FB_GEN1(big, t, sz) \
+ FB_GEN1(little, t, sz)
+
+#define FB_GEN(sz) \
+ FB_GEN2(uint##sz##_t, sz) \
+ FB_GEN2(int##sz##_t, sz)
+
+class Endian {
+ public:
+ enum class Order : uint8_t {
+ LITTLE,
+ BIG
+ };
+
+ static constexpr Order order = kIsLittleEndian ? Order::LITTLE : Order::BIG;
+
+ template <class T> static T swap(T x) {
+ return folly::detail::EndianInt<T>::swap(x);
+ }
+ template <class T> static T big(T x) {
+ return folly::detail::EndianInt<T>::big(x);
+ }
+ template <class T> static T little(T x) {
+ return folly::detail::EndianInt<T>::little(x);
+ }
+
+#if !defined(__ANDROID__)
+ FB_GEN(64)
+ FB_GEN(32)
+ FB_GEN(16)
+ FB_GEN(8)
+#endif
+};
+
+#undef FB_GEN
+#undef FB_GEN2
+#undef FB_GEN1
+
+
+template <class T, class Enable=void> struct Unaligned;
+
+/**
+ * Representation of an unaligned value of a POD type.
+ */
+FOLLY_PACK_PUSH
+template <class T>
+struct Unaligned<
+ T,
+ typename std::enable_if<std::is_pod<T>::value>::type> {
+ Unaligned() = default; // uninitialized
+ /* implicit */ Unaligned(T v) : value(v) { }
+ T value;
+} FOLLY_PACK_ATTR;
+FOLLY_PACK_POP
+
+/**
+ * Read an unaligned value of type T and return it.
+ */
+template <class T>
+inline T loadUnaligned(const void* p) {
+ static_assert(sizeof(Unaligned<T>) == sizeof(T), "Invalid unaligned size");
+ static_assert(alignof(Unaligned<T>) == 1, "Invalid alignment");
+ if (kHasUnalignedAccess) {
+ return static_cast<const Unaligned<T>*>(p)->value;
+ } else {
+ T value;
+ memcpy(&value, p, sizeof(T));
+ return value;
+ }
+}
+
+/**
+ * Write an unaligned value of type T.
+ */
+template <class T>
+inline void storeUnaligned(void* p, T value) {
+ static_assert(sizeof(Unaligned<T>) == sizeof(T), "Invalid unaligned size");
+ static_assert(alignof(Unaligned<T>) == 1, "Invalid alignment");
+ if (kHasUnalignedAccess) {
+ // Prior to C++14, the spec says that a placement new like this
+ // is required to check that p is not nullptr, and to do nothing
+ // if p is a nullptr. By assuming it's not a nullptr, we get a
+ // nice loud segfault in optimized builds if p is nullptr, rather
+ // than just silently doing nothing.
+ folly::assume(p != nullptr);
+ new (p) Unaligned<T>(value);
+ } else {
+ memcpy(p, &value, sizeof(T));
+ }
+}
+
+template <typename T>
+T bitReverse(T n) {
+ auto m = static_cast<typename std::make_unsigned<T>::type>(n);
+ m = ((m & 0xAAAAAAAAAAAAAAAA) >> 1) | ((m & 0x5555555555555555) << 1);
+ m = ((m & 0xCCCCCCCCCCCCCCCC) >> 2) | ((m & 0x3333333333333333) << 2);
+ m = ((m & 0xF0F0F0F0F0F0F0F0) >> 4) | ((m & 0x0F0F0F0F0F0F0F0F) << 4);
+ return static_cast<T>(Endian::swap(m));
+}
+
+} // namespace folly
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