From d1de75bf540f091b4dfc860713d556e578c0f158 Mon Sep 17 00:00:00 2001 From: Abseil Team Date: Fri, 25 Sep 2020 10:29:25 -0700 Subject: Export of internal Abseil changes -- f50d25c8f8491ef7031cbbcad78edd15f98c2bd1 by Abseil Team : Add myriad2 to HAVE_MMAP Remove mutex_nonprod and associated defines. PiperOrigin-RevId: 333759830 -- 25ef4c577ea983aa3fcd6cfe2af6cdc62a06f520 by Samuel Benzaquen : Internal refactor. Represent the data with a union to allow for better constexpr support in the future. PiperOrigin-RevId: 333756733 GitOrigin-RevId: f50d25c8f8491ef7031cbbcad78edd15f98c2bd1 Change-Id: Ieecd2c47cb20de638726eb3f9fc2e5682d05dcca --- absl/strings/cord.h | 95 ++++++++++++++++++++++++++--------------------------- 1 file changed, 46 insertions(+), 49 deletions(-) (limited to 'absl/strings/cord.h') diff --git a/absl/strings/cord.h b/absl/strings/cord.h index b8b251b0..653a1181 100644 --- a/absl/strings/cord.h +++ b/absl/strings/cord.h @@ -644,14 +644,12 @@ class Cord { // InlineRep holds either a tree pointer, or an array of kMaxInline bytes. class InlineRep { public: - static constexpr unsigned char kMaxInline = 15; + static constexpr unsigned char kMaxInline = cord_internal::kMaxInline; static_assert(kMaxInline >= sizeof(absl::cord_internal::CordRep*), ""); - // Tag byte & kMaxInline means we are storing a pointer. - static constexpr unsigned char kTreeFlag = 1 << 4; - // Tag byte & kProfiledFlag means we are profiling the Cord. - static constexpr unsigned char kProfiledFlag = 1 << 5; + static constexpr unsigned char kTreeFlag = cord_internal::kTreeFlag; + static constexpr unsigned char kProfiledFlag = cord_internal::kProfiledFlag; - constexpr InlineRep() : data_{} {} + constexpr InlineRep() : data_() {} InlineRep(const InlineRep& src); InlineRep(InlineRep&& src); InlineRep& operator=(const InlineRep& src); @@ -684,16 +682,16 @@ class Cord { void GetAppendRegion(char** region, size_t* size, size_t max_length); void GetAppendRegion(char** region, size_t* size); bool IsSame(const InlineRep& other) const { - return memcmp(data_, other.data_, sizeof(data_)) == 0; + return memcmp(&data_, &other.data_, sizeof(data_)) == 0; } int BitwiseCompare(const InlineRep& other) const { uint64_t x, y; - // Use memcpy to avoid anti-aliasing issues. - memcpy(&x, data_, sizeof(x)); - memcpy(&y, other.data_, sizeof(y)); + // Use memcpy to avoid aliasing issues. + memcpy(&x, &data_, sizeof(x)); + memcpy(&y, &other.data_, sizeof(y)); if (x == y) { - memcpy(&x, data_ + 8, sizeof(x)); - memcpy(&y, other.data_ + 8, sizeof(y)); + memcpy(&x, reinterpret_cast(&data_) + 8, sizeof(x)); + memcpy(&y, reinterpret_cast(&other.data_) + 8, sizeof(y)); if (x == y) return 0; } return absl::big_endian::FromHost64(x) < absl::big_endian::FromHost64(y) @@ -706,16 +704,16 @@ class Cord { // to 15 bytes does not cause a memory allocation. absl::strings_internal::STLStringResizeUninitialized(dst, sizeof(data_) - 1); - memcpy(&(*dst)[0], data_, sizeof(data_) - 1); + memcpy(&(*dst)[0], &data_, sizeof(data_) - 1); // erase is faster than resize because the logic for memory allocation is // not needed. - dst->erase(data_[kMaxInline]); + dst->erase(tagged_size()); } // Copies the inline contents into `dst`. Assumes the cord is not empty. void CopyToArray(char* dst) const; - bool is_tree() const { return data_[kMaxInline] > kMaxInline; } + bool is_tree() const { return tagged_size() > kMaxInline; } private: friend class Cord; @@ -724,10 +722,18 @@ class Cord { // Unrefs the tree, stops profiling, and zeroes the contents void ClearSlow(); - // If the data has length <= kMaxInline, we store it in data_[0..len-1], - // and store the length in data_[kMaxInline]. Else we store it in a tree - // and store a pointer to that tree in data_[0..sizeof(CordRep*)-1]. - alignas(absl::cord_internal::CordRep*) char data_[kMaxInline + 1]; + void ResetToEmpty() { data_ = {}; } + + // This uses reinterpret_cast instead of the union to avoid accessing the + // inactive union element. The tagged size is not a common prefix. + void set_tagged_size(char new_tag) { + reinterpret_cast(&data_)[kMaxInline] = new_tag; + } + char tagged_size() const { + return reinterpret_cast(&data_)[kMaxInline]; + } + + cord_internal::InlineData data_; }; InlineRep contents_; @@ -879,12 +885,12 @@ Cord MakeCordFromExternal(absl::string_view data, Releaser&& releaser) { } inline Cord::InlineRep::InlineRep(const Cord::InlineRep& src) { - cord_internal::SmallMemmove(data_, src.data_, sizeof(data_)); + data_ = src.data_; } inline Cord::InlineRep::InlineRep(Cord::InlineRep&& src) { - memcpy(data_, src.data_, sizeof(data_)); - memset(src.data_, 0, sizeof(data_)); + data_ = src.data_; + src.ResetToEmpty(); } inline Cord::InlineRep& Cord::InlineRep::operator=(const Cord::InlineRep& src) { @@ -892,7 +898,7 @@ inline Cord::InlineRep& Cord::InlineRep::operator=(const Cord::InlineRep& src) { return *this; } if (!is_tree() && !src.is_tree()) { - cord_internal::SmallMemmove(data_, src.data_, sizeof(data_)); + data_ = src.data_; return *this; } AssignSlow(src); @@ -904,8 +910,8 @@ inline Cord::InlineRep& Cord::InlineRep::operator=( if (is_tree()) { ClearSlow(); } - memcpy(data_, src.data_, sizeof(data_)); - memset(src.data_, 0, sizeof(data_)); + data_ = src.data_; + src.ResetToEmpty(); return *this; } @@ -914,43 +920,39 @@ inline void Cord::InlineRep::Swap(Cord::InlineRep* rhs) { return; } - Cord::InlineRep tmp; - cord_internal::SmallMemmove(tmp.data_, data_, sizeof(data_)); - cord_internal::SmallMemmove(data_, rhs->data_, sizeof(data_)); - cord_internal::SmallMemmove(rhs->data_, tmp.data_, sizeof(data_)); + std::swap(data_, rhs->data_); } inline const char* Cord::InlineRep::data() const { - return is_tree() ? nullptr : data_; + return is_tree() ? nullptr : data_.as_chars; } inline absl::cord_internal::CordRep* Cord::InlineRep::tree() const { if (is_tree()) { - absl::cord_internal::CordRep* rep; - memcpy(&rep, data_, sizeof(rep)); - return rep; + return data_.as_tree.rep; } else { return nullptr; } } -inline bool Cord::InlineRep::empty() const { return data_[kMaxInline] == 0; } +inline bool Cord::InlineRep::empty() const { return tagged_size() == 0; } inline size_t Cord::InlineRep::size() const { - const char tag = data_[kMaxInline]; + const char tag = tagged_size(); if (tag <= kMaxInline) return tag; return static_cast(tree()->length); } inline void Cord::InlineRep::set_tree(absl::cord_internal::CordRep* rep) { if (rep == nullptr) { - memset(data_, 0, sizeof(data_)); + ResetToEmpty(); } else { bool was_tree = is_tree(); - memcpy(data_, &rep, sizeof(rep)); - memset(data_ + sizeof(rep), 0, sizeof(data_) - sizeof(rep) - 1); + data_.as_tree = {rep, {}, tagged_size()}; if (!was_tree) { - data_[kMaxInline] = kTreeFlag; + // If we were not a tree already, set the tag. + // Otherwise, leave it alone because it might have the profile bit on. + set_tagged_size(kTreeFlag); } } } @@ -961,25 +963,20 @@ inline void Cord::InlineRep::replace_tree(absl::cord_internal::CordRep* rep) { set_tree(rep); return; } - memcpy(data_, &rep, sizeof(rep)); - memset(data_ + sizeof(rep), 0, sizeof(data_) - sizeof(rep) - 1); + data_.as_tree = {rep, {}, tagged_size()}; } inline absl::cord_internal::CordRep* Cord::InlineRep::clear() { - const char tag = data_[kMaxInline]; - absl::cord_internal::CordRep* result = nullptr; - if (tag > kMaxInline) { - memcpy(&result, data_, sizeof(result)); - } - memset(data_, 0, sizeof(data_)); // Clear the cord + absl::cord_internal::CordRep* result = tree(); + ResetToEmpty(); return result; } inline void Cord::InlineRep::CopyToArray(char* dst) const { assert(!is_tree()); - size_t n = data_[kMaxInline]; + size_t n = tagged_size(); assert(n != 0); - cord_internal::SmallMemmove(dst, data_, n); + cord_internal::SmallMemmove(dst, data_.as_chars, n); } constexpr inline Cord::Cord() noexcept {} -- cgit v1.2.3