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-rw-r--r--absl/strings/str_cat.cc178
-rw-r--r--absl/strings/str_cat.h152
2 files changed, 196 insertions, 134 deletions
diff --git a/absl/strings/str_cat.cc b/absl/strings/str_cat.cc
index 5ec02995..2e49c31b 100644
--- a/absl/strings/str_cat.cc
+++ b/absl/strings/str_cat.cc
@@ -14,9 +14,17 @@
#include "absl/strings/str_cat.h"
+#include <assert.h>
+
+#include <algorithm>
+#include <cstddef>
#include <cstdint>
+#include <cstring>
#include <string>
+#include "absl/strings/ascii.h"
+#include "absl/strings/internal/resize_uninitialized.h"
+#include "absl/strings/numbers.h"
#include "absl/strings/string_view.h"
namespace absl {
@@ -29,26 +37,170 @@ ABSL_NAMESPACE_BEGIN
// of a mix of raw C strings, string_views, strings, and integer values.
// ----------------------------------------------------------------------
+// Append is merely a version of memcpy that returns the address of the byte
+// after the area just overwritten.
+static char* Append(char* out, const AlphaNum& x) {
+ // memcpy is allowed to overwrite arbitrary memory, so doing this after the
+ // call would force an extra fetch of x.size().
+ char* after = out + x.size();
+ if (x.size() != 0) {
+ memcpy(out, x.data(), x.size());
+ }
+ return after;
+}
+
+std::string StrCat(const AlphaNum& a, const AlphaNum& b) {
+ std::string result;
+ absl::strings_internal::STLStringResizeUninitialized(&result,
+ a.size() + b.size());
+ char* const begin = &result[0];
+ char* out = begin;
+ out = Append(out, a);
+ out = Append(out, b);
+ assert(out == begin + result.size());
+ return result;
+}
+
+std::string StrCat(const AlphaNum& a, const AlphaNum& b, const AlphaNum& c) {
+ std::string result;
+ strings_internal::STLStringResizeUninitialized(
+ &result, a.size() + b.size() + c.size());
+ char* const begin = &result[0];
+ char* out = begin;
+ out = Append(out, a);
+ out = Append(out, b);
+ out = Append(out, c);
+ assert(out == begin + result.size());
+ return result;
+}
+
+std::string StrCat(const AlphaNum& a, const AlphaNum& b, const AlphaNum& c,
+ const AlphaNum& d) {
+ std::string result;
+ strings_internal::STLStringResizeUninitialized(
+ &result, a.size() + b.size() + c.size() + d.size());
+ char* const begin = &result[0];
+ char* out = begin;
+ out = Append(out, a);
+ out = Append(out, b);
+ out = Append(out, c);
+ out = Append(out, d);
+ assert(out == begin + result.size());
+ return result;
+}
+
namespace strings_internal {
-bool HaveOverlap(const std::string& x, absl::string_view y) {
- if (y.empty()) return false;
- // TODO(b/290623057): Re-evaluate the check below: it detects when buffers
- // overlap (which is good) but it also introduces undefined behaviour when
- // buffers don't overlap (substracting pointers that do not belong to the same
- // array is UB [expr.add]). In other words, if compiler assumes that a program
- // never has UB, then it can replace `assert(HaveOverlap(x, y))` with
- // `assert(false)`.
- return (uintptr_t(y.data() - x.data()) <= uintptr_t(x.size()));
+// Do not call directly - these are not part of the public API.
+std::string CatPieces(std::initializer_list<absl::string_view> pieces) {
+ std::string result;
+ size_t total_size = 0;
+ for (absl::string_view piece : pieces) total_size += piece.size();
+ strings_internal::STLStringResizeUninitialized(&result, total_size);
+
+ char* const begin = &result[0];
+ char* out = begin;
+ for (absl::string_view piece : pieces) {
+ const size_t this_size = piece.size();
+ if (this_size != 0) {
+ memcpy(out, piece.data(), this_size);
+ out += this_size;
+ }
+ }
+ assert(out == begin + result.size());
+ return result;
}
-#if defined(__GNUC__) && !defined(__clang__)
-char* AppendAlphaNum(char* dst, const AlphaNum& a) {
- return std::copy_n(a.data(), a.size(), dst);
+// It's possible to call StrAppend with an absl::string_view that is itself a
+// fragment of the string we're appending to. However the results of this are
+// random. Therefore, check for this in debug mode. Use unsigned math so we
+// only have to do one comparison. Note, there's an exception case: appending an
+// empty string is always allowed.
+#define ASSERT_NO_OVERLAP(dest, src) \
+ assert(((src).size() == 0) || \
+ (uintptr_t((src).data() - (dest).data()) > uintptr_t((dest).size())))
+
+void AppendPieces(std::string* dest,
+ std::initializer_list<absl::string_view> pieces) {
+ size_t old_size = dest->size();
+ size_t total_size = old_size;
+ for (absl::string_view piece : pieces) {
+ ASSERT_NO_OVERLAP(*dest, piece);
+ total_size += piece.size();
+ }
+ strings_internal::STLStringResizeUninitializedAmortized(dest, total_size);
+
+ char* const begin = &(*dest)[0];
+ char* out = begin + old_size;
+ for (absl::string_view piece : pieces) {
+ const size_t this_size = piece.size();
+ if (this_size != 0) {
+ memcpy(out, piece.data(), this_size);
+ out += this_size;
+ }
+ }
+ assert(out == begin + dest->size());
}
-#endif
} // namespace strings_internal
+void StrAppend(std::string* dest, const AlphaNum& a) {
+ ASSERT_NO_OVERLAP(*dest, a);
+ std::string::size_type old_size = dest->size();
+ strings_internal::STLStringResizeUninitializedAmortized(dest,
+ old_size + a.size());
+ char* const begin = &(*dest)[0];
+ char* out = begin + old_size;
+ out = Append(out, a);
+ assert(out == begin + dest->size());
+}
+
+void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b) {
+ ASSERT_NO_OVERLAP(*dest, a);
+ ASSERT_NO_OVERLAP(*dest, b);
+ std::string::size_type old_size = dest->size();
+ strings_internal::STLStringResizeUninitializedAmortized(
+ dest, old_size + a.size() + b.size());
+ char* const begin = &(*dest)[0];
+ char* out = begin + old_size;
+ out = Append(out, a);
+ out = Append(out, b);
+ assert(out == begin + dest->size());
+}
+
+void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b,
+ const AlphaNum& c) {
+ ASSERT_NO_OVERLAP(*dest, a);
+ ASSERT_NO_OVERLAP(*dest, b);
+ ASSERT_NO_OVERLAP(*dest, c);
+ std::string::size_type old_size = dest->size();
+ strings_internal::STLStringResizeUninitializedAmortized(
+ dest, old_size + a.size() + b.size() + c.size());
+ char* const begin = &(*dest)[0];
+ char* out = begin + old_size;
+ out = Append(out, a);
+ out = Append(out, b);
+ out = Append(out, c);
+ assert(out == begin + dest->size());
+}
+
+void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b,
+ const AlphaNum& c, const AlphaNum& d) {
+ ASSERT_NO_OVERLAP(*dest, a);
+ ASSERT_NO_OVERLAP(*dest, b);
+ ASSERT_NO_OVERLAP(*dest, c);
+ ASSERT_NO_OVERLAP(*dest, d);
+ std::string::size_type old_size = dest->size();
+ strings_internal::STLStringResizeUninitializedAmortized(
+ dest, old_size + a.size() + b.size() + c.size() + d.size());
+ char* const begin = &(*dest)[0];
+ char* out = begin + old_size;
+ out = Append(out, a);
+ out = Append(out, b);
+ out = Append(out, c);
+ out = Append(out, d);
+ assert(out == begin + dest->size());
+}
+
ABSL_NAMESPACE_END
} // namespace absl
diff --git a/absl/strings/str_cat.h b/absl/strings/str_cat.h
index f5f2c016..d5f71ff0 100644
--- a/absl/strings/str_cat.h
+++ b/absl/strings/str_cat.h
@@ -91,9 +91,7 @@
#include <array>
#include <cstdint>
#include <cstring>
-#include <functional>
#include <string>
-#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
@@ -101,7 +99,6 @@
#include "absl/base/attributes.h"
#include "absl/base/port.h"
#include "absl/strings/internal/has_absl_stringify.h"
-#include "absl/strings/internal/resize_uninitialized.h"
#include "absl/strings/internal/stringify_sink.h"
#include "absl/strings/numbers.h"
#include "absl/strings/string_view.h"
@@ -412,93 +409,6 @@ class AlphaNum {
char digits_[numbers_internal::kFastToBufferSize];
};
-namespace strings_internal {
-
-// Inlining this function improves performance. However, on GCC this triggers
-// [-Werror=stringop-overflow=], and in that case we split declaration and
-// definition as a workaround.
-#if defined(__GNUC__) && !defined(__clang__)
-char* AppendAlphaNum(char* dst, const AlphaNum& a);
-#else
-inline char* AppendAlphaNum(char* dst, const AlphaNum& a) {
- return std::copy_n(a.data(), a.size(), dst);
-}
-#endif
-
-// It's possible to call StrAppend with an absl::string_view that is itself a
-// fragment of the string we're appending to. However the results of this are
-// UB. Therefore, check for this in debug mode. Use unsigned math so we
-// only have to do one comparison. Note, there's an exception case: appending an
-// empty string is always allowed.
-bool HaveOverlap(const std::string& x, absl::string_view y);
-
-// C++14 compatible alternative to left
-// https://en.cppreference.com/w/cpp/language/fold expression.
-// TODO(b/290784225): Remove `FoldLeft` once Abseil drops C++14 support.
-template <typename F, typename Acc>
-auto FoldLeft(const F&, Acc&& acc) {
- return std::forward<Acc>(acc);
-}
-template <typename F, typename Acc, typename First, typename... Rest>
-auto FoldLeft(const F& f, Acc&& acc, First&& first, Rest&&... rest) {
- return FoldLeft(f, f(std::forward<Acc>(acc), std::forward<First>(first)),
- std::forward<Rest>(rest)...);
-}
-
-template <std::size_t... Indices, typename Tuple>
-inline void StrAppendTemplate(std::index_sequence<Indices...>,
- std::string* dest, Tuple args) {
- // Note on `Is` and `Tuple`:
- //
- // The goal is to pass N arguments to `StrAppend` and retain `N` as a
- // compile-time constant. Thus, we cannot use dynamically sized collections
- // such as `absl::Span` or `std::initialized_list`: `std::tuple` comes to
- // the rescue.
- // `Tuple` is a fixed-sized collection of N elements of `const AlphaNum&`.
- // `Indices` is deduced from `std::make_index_sequence<N>` and is used as a
- // helper to writing Fold expressions on `Tuple`.
- assert(FoldLeft(std::logical_and<>{},
- !HaveOverlap(*dest, std::get<Indices>(args).Piece())...));
- size_t old_size = dest->size();
- size_t new_size =
- FoldLeft(std::plus<>{}, old_size, std::get<Indices>(args).size()...);
- strings_internal::STLStringResizeUninitializedAmortized(dest, new_size);
- FoldLeft(AppendAlphaNum, &(*dest)[old_size], std::get<Indices>(args)...);
-}
-
-template <std::size_t... Indices, typename Tuple>
-inline std::string StrCatTemplate(std::index_sequence<Indices...>, Tuple args) {
- // See implementation comments in `StrAppendTemplate`.
- std::string dest;
- size_t size = FoldLeft(std::plus<size_t>{}, size_t{0},
- std::get<Indices>(args).size()...);
- strings_internal::STLStringResizeUninitializedAmortized(&dest, size);
- FoldLeft(AppendAlphaNum, &dest[0], std::get<Indices>(args)...);
- return dest;
-}
-
-// Template functions `StrAppendImpl` and `StrCatImpl` are not exported directly
-// due to historical reasons: there are many existing dependencies that expect
-// 0-4 argument overloads to be non-template functions. Hence implementations
-// are wrapped to keep the compatibility (0-4 arguments only, 5+ arguments are
-// templates).
-
-template <typename... AV>
-inline void StrAppendImpl(std::string* dest, const AV&... args) {
- strings_internal::StrAppendTemplate(
- std::make_index_sequence<sizeof...(AV)>{}, dest,
- std::forward_as_tuple(static_cast<const AlphaNum&>(args)...));
-}
-
-template <typename... AV>
-inline std::string StrCatImpl(const AV&... args) {
- return strings_internal::StrCatTemplate(
- std::make_index_sequence<sizeof...(AV)>{},
- std::forward_as_tuple(static_cast<const AlphaNum&>(args)...));
-}
-
-} // namespace strings_internal
-
// -----------------------------------------------------------------------------
// StrCat()
// -----------------------------------------------------------------------------
@@ -526,32 +436,36 @@ inline std::string StrCatImpl(const AV&... args) {
// quadratic time operation with O(n) dynamic allocations.
//
// See `StrAppend()` below for more information.
+
+namespace strings_internal {
+
+// Do not call directly - this is not part of the public API.
+std::string CatPieces(std::initializer_list<absl::string_view> pieces);
+void AppendPieces(std::string* dest,
+ std::initializer_list<absl::string_view> pieces);
+
+} // namespace strings_internal
+
ABSL_MUST_USE_RESULT inline std::string StrCat() { return std::string(); }
+
ABSL_MUST_USE_RESULT inline std::string StrCat(const AlphaNum& a) {
return std::string(a.data(), a.size());
}
-ABSL_MUST_USE_RESULT inline std::string StrCat(const AlphaNum& a,
- const AlphaNum& b) {
- return strings_internal::StrCatImpl(a, b);
-}
-ABSL_MUST_USE_RESULT inline std::string StrCat(const AlphaNum& a,
- const AlphaNum& b,
- const AlphaNum& c) {
- return strings_internal::StrCatImpl(a, b, c);
-}
-ABSL_MUST_USE_RESULT inline std::string StrCat(const AlphaNum& a,
- const AlphaNum& b,
- const AlphaNum& c,
- const AlphaNum& d) {
- return strings_internal::StrCatImpl(a, b, c, d);
-}
+
+ABSL_MUST_USE_RESULT std::string StrCat(const AlphaNum& a, const AlphaNum& b);
+ABSL_MUST_USE_RESULT std::string StrCat(const AlphaNum& a, const AlphaNum& b,
+ const AlphaNum& c);
+ABSL_MUST_USE_RESULT std::string StrCat(const AlphaNum& a, const AlphaNum& b,
+ const AlphaNum& c, const AlphaNum& d);
// Support 5 or more arguments
template <typename... AV>
ABSL_MUST_USE_RESULT inline std::string StrCat(
const AlphaNum& a, const AlphaNum& b, const AlphaNum& c, const AlphaNum& d,
const AlphaNum& e, const AV&... args) {
- return strings_internal::StrCatImpl(a, b, c, d, e, args...);
+ return strings_internal::CatPieces(
+ {a.Piece(), b.Piece(), c.Piece(), d.Piece(), e.Piece(),
+ static_cast<const AlphaNum&>(args).Piece()...});
}
// -----------------------------------------------------------------------------
@@ -580,27 +494,23 @@ ABSL_MUST_USE_RESULT inline std::string StrCat(
// std::string s = "foobar";
// absl::string_view p = s;
// StrAppend(&s, p);
+
inline void StrAppend(std::string*) {}
-inline void StrAppend(std::string* dest, const AlphaNum& a) {
- strings_internal::StrAppendImpl(dest, a);
-}
-inline void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b) {
- strings_internal::StrAppendImpl(dest, a, b);
-}
-inline void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b,
- const AlphaNum& c) {
- strings_internal::StrAppendImpl(dest, a, b, c);
-}
-inline void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b,
- const AlphaNum& c, const AlphaNum& d) {
- strings_internal::StrAppendImpl(dest, a, b, c, d);
-}
+void StrAppend(std::string* dest, const AlphaNum& a);
+void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b);
+void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b,
+ const AlphaNum& c);
+void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b,
+ const AlphaNum& c, const AlphaNum& d);
+
// Support 5 or more arguments
template <typename... AV>
inline void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b,
const AlphaNum& c, const AlphaNum& d, const AlphaNum& e,
const AV&... args) {
- strings_internal::StrAppendImpl(dest, a, b, c, d, e, args...);
+ strings_internal::AppendPieces(
+ dest, {a.Piece(), b.Piece(), c.Piece(), d.Piece(), e.Piece(),
+ static_cast<const AlphaNum&>(args).Piece()...});
}
// Helper function for the future StrCat default floating-point format, %.6g
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-23 01:53:27 +0000