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//
// Copyright 2017 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.
//
// -----------------------------------------------------------------------------
// File: str_cat.h
// -----------------------------------------------------------------------------
//
// This package contains functions for efficiently concatenating and appending
// strings: `StrCat()` and `StrAppend()`. Most of the work within these routines
// is actually handled through use of a special AlphaNum type, which was
// designed to be used as a parameter type that efficiently manages conversion
// to strings and avoids copies in the above operations.
//
// Any routine accepting either a string or a number may accept `AlphaNum`.
// The basic idea is that by accepting a `const AlphaNum &` as an argument
// to your function, your callers will automagically convert bools, integers,
// and floating point values to strings for you.
//
// NOTE: Use of `AlphaNum` outside of the //absl/strings package is unsupported
// except for the specific case of function parameters of type `AlphaNum` or
// `const AlphaNum &`. In particular, instantiating `AlphaNum` directly as a
// stack variable is not supported.
//
// Conversion from 8-bit values is not accepted because, if it were, then an
// attempt to pass ':' instead of ":" might result in a 58 ending up in your
// result.
//
// Bools convert to "0" or "1". Pointers to types other than `char *` are not
// valid inputs. No output is generated for null `char *` pointers.
//
// Floating point numbers are formatted with six-digit precision, which is
// the default for "std::cout <<" or printf "%g" (the same as "%.6g").
//
// You can convert to hexadecimal output rather than decimal output using the
// `Hex` type contained here. To do so, pass `Hex(my_int)` as a parameter to
// `StrCat()` or `StrAppend()`. You may specify a minimum hex field width using
// a `PadSpec` enum.
//
// User-defined types can be formatted with the `AbslStringify()` customization
// point. The API relies on detecting an overload in the user-defined type's
// namespace of a free (non-member) `AbslStringify()` function as a definition
// (typically declared as a friend and implemented in-line.
// with the following signature:
//
// class MyClass { ... };
//
// template <typename Sink>
// void AbslStringify(Sink& sink, const MyClass& value);
//
// An `AbslStringify()` overload for a type should only be declared in the same
// file and namespace as said type.
//
// Note that `AbslStringify()` also supports use with `absl::StrFormat()` and
// `absl::Substitute()`.
//
// Example:
//
// struct Point {
// // To add formatting support to `Point`, we simply need to add a free
// // (non-member) function `AbslStringify()`. This method specifies how
// // Point should be printed when absl::StrCat() is called on it. You can add
// // such a free function using a friend declaration within the body of the
// // class. The sink parameter is a templated type to avoid requiring
// // dependencies.
// template <typename Sink> friend void AbslStringify(Sink&
// sink, const Point& p) {
// absl::Format(&sink, "(%v, %v)", p.x, p.y);
// }
//
// int x;
// int y;
// };
// -----------------------------------------------------------------------------
#ifndef ABSL_STRINGS_STR_CAT_H_
#define ABSL_STRINGS_STR_CAT_H_
#include <algorithm>
#include <array>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <initializer_list>
#include <string>
#include <type_traits>
#include <utility>
#include <vector>
#include "absl/base/attributes.h"
#include "absl/base/nullability.h"
#include "absl/base/port.h"
#include "absl/meta/type_traits.h"
#include "absl/strings/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"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace strings_internal {
// AlphaNumBuffer allows a way to pass a string to StrCat without having to do
// memory allocation. It is simply a pair of a fixed-size character array, and
// a size. Please don't use outside of absl, yet.
template <size_t max_size>
struct AlphaNumBuffer {
std::array<char, max_size> data;
size_t size;
};
} // namespace strings_internal
// Enum that specifies the number of significant digits to return in a `Hex` or
// `Dec` conversion and fill character to use. A `kZeroPad2` value, for example,
// would produce hexadecimal strings such as "0a","0f" and a 'kSpacePad5' value
// would produce hexadecimal strings such as " a"," f".
enum PadSpec : uint8_t {
kNoPad = 1,
kZeroPad2,
kZeroPad3,
kZeroPad4,
kZeroPad5,
kZeroPad6,
kZeroPad7,
kZeroPad8,
kZeroPad9,
kZeroPad10,
kZeroPad11,
kZeroPad12,
kZeroPad13,
kZeroPad14,
kZeroPad15,
kZeroPad16,
kZeroPad17,
kZeroPad18,
kZeroPad19,
kZeroPad20,
kSpacePad2 = kZeroPad2 + 64,
kSpacePad3,
kSpacePad4,
kSpacePad5,
kSpacePad6,
kSpacePad7,
kSpacePad8,
kSpacePad9,
kSpacePad10,
kSpacePad11,
kSpacePad12,
kSpacePad13,
kSpacePad14,
kSpacePad15,
kSpacePad16,
kSpacePad17,
kSpacePad18,
kSpacePad19,
kSpacePad20,
};
// -----------------------------------------------------------------------------
// Hex
// -----------------------------------------------------------------------------
//
// `Hex` stores a set of hexadecimal string conversion parameters for use
// within `AlphaNum` string conversions.
struct Hex {
uint64_t value;
uint8_t width;
char fill;
template <typename Int>
explicit Hex(
Int v, PadSpec spec = absl::kNoPad,
typename std::enable_if<sizeof(Int) == 1 &&
!std::is_pointer<Int>::value>::type* = nullptr)
: Hex(spec, static_cast<uint8_t>(v)) {}
template <typename Int>
explicit Hex(
Int v, PadSpec spec = absl::kNoPad,
typename std::enable_if<sizeof(Int) == 2 &&
!std::is_pointer<Int>::value>::type* = nullptr)
: Hex(spec, static_cast<uint16_t>(v)) {}
template <typename Int>
explicit Hex(
Int v, PadSpec spec = absl::kNoPad,
typename std::enable_if<sizeof(Int) == 4 &&
!std::is_pointer<Int>::value>::type* = nullptr)
: Hex(spec, static_cast<uint32_t>(v)) {}
template <typename Int>
explicit Hex(
Int v, PadSpec spec = absl::kNoPad,
typename std::enable_if<sizeof(Int) == 8 &&
!std::is_pointer<Int>::value>::type* = nullptr)
: Hex(spec, static_cast<uint64_t>(v)) {}
template <typename Pointee>
explicit Hex(absl::Nullable<Pointee*> v, PadSpec spec = absl::kNoPad)
: Hex(spec, reinterpret_cast<uintptr_t>(v)) {}
template <typename S>
friend void AbslStringify(S& sink, Hex hex) {
static_assert(
numbers_internal::kFastToBufferSize >= 32,
"This function only works when output buffer >= 32 bytes long");
char buffer[numbers_internal::kFastToBufferSize];
char* const end = &buffer[numbers_internal::kFastToBufferSize];
auto real_width =
absl::numbers_internal::FastHexToBufferZeroPad16(hex.value, end - 16);
if (real_width >= hex.width) {
sink.Append(absl::string_view(end - real_width, real_width));
} else {
// Pad first 16 chars because FastHexToBufferZeroPad16 pads only to 16 and
// max pad width can be up to 20.
std::memset(end - 32, hex.fill, 16);
// Patch up everything else up to the real_width.
std::memset(end - real_width - 16, hex.fill, 16);
sink.Append(absl::string_view(end - hex.width, hex.width));
}
}
private:
Hex(PadSpec spec, uint64_t v)
: value(v),
width(spec == absl::kNoPad
? 1
: spec >= absl::kSpacePad2 ? spec - absl::kSpacePad2 + 2
: spec - absl::kZeroPad2 + 2),
fill(spec >= absl::kSpacePad2 ? ' ' : '0') {}
};
// -----------------------------------------------------------------------------
// Dec
// -----------------------------------------------------------------------------
//
// `Dec` stores a set of decimal string conversion parameters for use
// within `AlphaNum` string conversions. Dec is slower than the default
// integer conversion, so use it only if you need padding.
struct Dec {
uint64_t value;
uint8_t width;
char fill;
bool neg;
template <typename Int>
explicit Dec(Int v, PadSpec spec = absl::kNoPad,
typename std::enable_if<(sizeof(Int) <= 8)>::type* = nullptr)
: value(v >= 0 ? static_cast<uint64_t>(v)
: uint64_t{0} - static_cast<uint64_t>(v)),
width(spec == absl::kNoPad ? 1
: spec >= absl::kSpacePad2 ? spec - absl::kSpacePad2 + 2
: spec - absl::kZeroPad2 + 2),
fill(spec >= absl::kSpacePad2 ? ' ' : '0'),
neg(v < 0) {}
template <typename S>
friend void AbslStringify(S& sink, Dec dec) {
assert(dec.width <= numbers_internal::kFastToBufferSize);
char buffer[numbers_internal::kFastToBufferSize];
char* const end = &buffer[numbers_internal::kFastToBufferSize];
char* const minfill = end - dec.width;
char* writer = end;
uint64_t val = dec.value;
while (val > 9) {
*--writer = '0' + (val % 10);
val /= 10;
}
*--writer = '0' + static_cast<char>(val);
if (dec.neg) *--writer = '-';
ptrdiff_t fillers = writer - minfill;
if (fillers > 0) {
// Tricky: if the fill character is ' ', then it's <fill><+/-><digits>
// But...: if the fill character is '0', then it's <+/-><fill><digits>
bool add_sign_again = false;
if (dec.neg && dec.fill == '0') { // If filling with '0',
++writer; // ignore the sign we just added
add_sign_again = true; // and re-add the sign later.
}
writer -= fillers;
std::fill_n(writer, fillers, dec.fill);
if (add_sign_again) *--writer = '-';
}
sink.Append(absl::string_view(writer, static_cast<size_t>(end - writer)));
}
};
// -----------------------------------------------------------------------------
// AlphaNum
// -----------------------------------------------------------------------------
//
// The `AlphaNum` class acts as the main parameter type for `StrCat()` and
// `StrAppend()`, providing efficient conversion of numeric, boolean, decimal,
// and hexadecimal values (through the `Dec` and `Hex` types) into strings.
// `AlphaNum` should only be used as a function parameter. Do not instantiate
// `AlphaNum` directly as a stack variable.
class AlphaNum {
public:
// No bool ctor -- bools convert to an integral type.
// A bool ctor would also convert incoming pointers (bletch).
// Prevent brace initialization
template <typename T>
AlphaNum(std::initializer_list<T>) = delete; // NOLINT(runtime/explicit)
AlphaNum(int x) // NOLINT(runtime/explicit)
: piece_(digits_, static_cast<size_t>(
numbers_internal::FastIntToBuffer(x, digits_) -
&digits_[0])) {}
AlphaNum(unsigned int x) // NOLINT(runtime/explicit)
: piece_(digits_, static_cast<size_t>(
numbers_internal::FastIntToBuffer(x, digits_) -
&digits_[0])) {}
AlphaNum(long x) // NOLINT(*)
: piece_(digits_, static_cast<size_t>(
numbers_internal::FastIntToBuffer(x, digits_) -
&digits_[0])) {}
AlphaNum(unsigned long x) // NOLINT(*)
: piece_(digits_, static_cast<size_t>(
numbers_internal::FastIntToBuffer(x, digits_) -
&digits_[0])) {}
AlphaNum(long long x) // NOLINT(*)
: piece_(digits_, static_cast<size_t>(
numbers_internal::FastIntToBuffer(x, digits_) -
&digits_[0])) {}
AlphaNum(unsigned long long x) // NOLINT(*)
: piece_(digits_, static_cast<size_t>(
numbers_internal::FastIntToBuffer(x, digits_) -
&digits_[0])) {}
AlphaNum(float f) // NOLINT(runtime/explicit)
: piece_(digits_, numbers_internal::SixDigitsToBuffer(f, digits_)) {}
AlphaNum(double f) // NOLINT(runtime/explicit)
: piece_(digits_, numbers_internal::SixDigitsToBuffer(f, digits_)) {}
template <size_t size>
AlphaNum( // NOLINT(runtime/explicit)
const strings_internal::AlphaNumBuffer<size>& buf
ABSL_ATTRIBUTE_LIFETIME_BOUND)
: piece_(&buf.data[0], buf.size) {}
AlphaNum(absl::Nullable<const char*> c_str // NOLINT(runtime/explicit)
ABSL_ATTRIBUTE_LIFETIME_BOUND)
: piece_(NullSafeStringView(c_str)) {}
AlphaNum(absl::string_view pc // NOLINT(runtime/explicit)
ABSL_ATTRIBUTE_LIFETIME_BOUND)
: piece_(pc) {}
template <typename T, typename = typename std::enable_if<
HasAbslStringify<T>::value>::type>
AlphaNum( // NOLINT(runtime/explicit)
const T& v ABSL_ATTRIBUTE_LIFETIME_BOUND,
strings_internal::StringifySink&& sink ABSL_ATTRIBUTE_LIFETIME_BOUND = {})
: piece_(strings_internal::ExtractStringification(sink, v)) {}
template <typename Allocator>
AlphaNum( // NOLINT(runtime/explicit)
const std::basic_string<char, std::char_traits<char>, Allocator>& str
ABSL_ATTRIBUTE_LIFETIME_BOUND)
: piece_(str) {}
// Use string literals ":" instead of character literals ':'.
AlphaNum(char c) = delete; // NOLINT(runtime/explicit)
AlphaNum(const AlphaNum&) = delete;
AlphaNum& operator=(const AlphaNum&) = delete;
absl::string_view::size_type size() const { return piece_.size(); }
absl::Nullable<const char*> data() const { return piece_.data(); }
absl::string_view Piece() const { return piece_; }
// Match unscoped enums. Use integral promotion so that a `char`-backed
// enum becomes a wider integral type AlphaNum will accept.
template <typename T,
typename = typename std::enable_if<
std::is_enum<T>{} && std::is_convertible<T, int>{} &&
!HasAbslStringify<T>::value>::type>
AlphaNum(T e) // NOLINT(runtime/explicit)
: AlphaNum(+e) {}
// This overload matches scoped enums. We must explicitly cast to the
// underlying type, but use integral promotion for the same reason as above.
template <typename T,
typename std::enable_if<std::is_enum<T>{} &&
!std::is_convertible<T, int>{} &&
!HasAbslStringify<T>::value,
char*>::type = nullptr>
AlphaNum(T e) // NOLINT(runtime/explicit)
: AlphaNum(+static_cast<typename std::underlying_type<T>::type>(e)) {}
// vector<bool>::reference and const_reference require special help to
// convert to `AlphaNum` because it requires two user defined conversions.
template <
typename T,
typename std::enable_if<
std::is_class<T>::value &&
(std::is_same<T, std::vector<bool>::reference>::value ||
std::is_same<T, std::vector<bool>::const_reference>::value)>::type* =
nullptr>
AlphaNum(T e) : AlphaNum(static_cast<bool>(e)) {} // NOLINT(runtime/explicit)
private:
absl::string_view piece_;
char digits_[numbers_internal::kFastToBufferSize];
};
// -----------------------------------------------------------------------------
// StrCat()
// -----------------------------------------------------------------------------
//
// Merges given strings or numbers, using no delimiter(s), returning the merged
// result as a string.
//
// `StrCat()` is designed to be the fastest possible way to construct a string
// out of a mix of raw C strings, string_views, strings, bool values,
// and numeric values.
//
// Don't use `StrCat()` for user-visible strings. The localization process
// works poorly on strings built up out of fragments.
//
// For clarity and performance, don't use `StrCat()` when appending to a
// string. Use `StrAppend()` instead. In particular, avoid using any of these
// (anti-)patterns:
//
// str.append(StrCat(...))
// str += StrCat(...)
// str = StrCat(str, ...)
//
// The last case is the worst, with a potential to change a loop
// from a linear time operation with O(1) dynamic allocations into a
// 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(absl::Nonnull<std::string*> dest,
std::initializer_list<absl::string_view> pieces);
void STLStringAppendUninitializedAmortized(std::string* dest, size_t to_append);
// `SingleArgStrCat` overloads take built-in `int`, `long` and `long long` types
// (signed / unsigned) to avoid ambiguity on the call side. If we used int32_t
// and int64_t, then at least one of the three (`int` / `long` / `long long`)
// would have been ambiguous when passed to `SingleArgStrCat`.
std::string SingleArgStrCat(int x);
std::string SingleArgStrCat(unsigned int x);
std::string SingleArgStrCat(long x); // NOLINT
std::string SingleArgStrCat(unsigned long x); // NOLINT
std::string SingleArgStrCat(long long x); // NOLINT
std::string SingleArgStrCat(unsigned long long x); // NOLINT
std::string SingleArgStrCat(float x);
std::string SingleArgStrCat(double x);
// `SingleArgStrAppend` overloads are defined here for the same reasons as with
// `SingleArgStrCat` above.
void SingleArgStrAppend(std::string& str, int x);
void SingleArgStrAppend(std::string& str, unsigned int x);
void SingleArgStrAppend(std::string& str, long x); // NOLINT
void SingleArgStrAppend(std::string& str, unsigned long x); // NOLINT
void SingleArgStrAppend(std::string& str, long long x); // NOLINT
void SingleArgStrAppend(std::string& str, unsigned long long x); // NOLINT
template <typename T,
typename = std::enable_if_t<std::is_arithmetic<T>::value &&
!std::is_same<T, char>::value &&
!std::is_same<T, bool>::value>>
using EnableIfFastCase = T;
} // namespace strings_internal
ABSL_MUST_USE_RESULT inline std::string StrCat() { return std::string(); }
template <typename T>
ABSL_MUST_USE_RESULT inline std::string StrCat(
strings_internal::EnableIfFastCase<T> a) {
return strings_internal::SingleArgStrCat(a);
}
ABSL_MUST_USE_RESULT inline std::string StrCat(const AlphaNum& a) {
return std::string(a.data(), a.size());
}
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::CatPieces(
{a.Piece(), b.Piece(), c.Piece(), d.Piece(), e.Piece(),
static_cast<const AlphaNum&>(args).Piece()...});
}
// -----------------------------------------------------------------------------
// StrAppend()
// -----------------------------------------------------------------------------
//
// Appends a string or set of strings to an existing string, in a similar
// fashion to `StrCat()`.
//
// WARNING: `StrAppend(&str, a, b, c, ...)` requires that none of the
// a, b, c, parameters be a reference into str. For speed, `StrAppend()` does
// not try to check each of its input arguments to be sure that they are not
// a subset of the string being appended to. That is, while this will work:
//
// std::string s = "foo";
// s += s;
//
// This output is undefined:
//
// std::string s = "foo";
// StrAppend(&s, s);
//
// This output is undefined as well, since `absl::string_view` does not own its
// data:
//
// std::string s = "foobar";
// absl::string_view p = s;
// StrAppend(&s, p);
inline void StrAppend(absl::Nonnull<std::string*>) {}
void StrAppend(absl::Nonnull<std::string*> dest, const AlphaNum& a);
void StrAppend(absl::Nonnull<std::string*> dest, const AlphaNum& a,
const AlphaNum& b);
void StrAppend(absl::Nonnull<std::string*> dest, const AlphaNum& a,
const AlphaNum& b, const AlphaNum& c);
void StrAppend(absl::Nonnull<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(absl::Nonnull<std::string*> dest, const AlphaNum& a,
const AlphaNum& b, const AlphaNum& c, const AlphaNum& d,
const AlphaNum& e, const AV&... args) {
strings_internal::AppendPieces(
dest, {a.Piece(), b.Piece(), c.Piece(), d.Piece(), e.Piece(),
static_cast<const AlphaNum&>(args).Piece()...});
}
template <class String, class T>
std::enable_if_t<
std::is_integral<absl::strings_internal::EnableIfFastCase<T>>::value, void>
StrAppend(absl::Nonnull<String*> result, T i) {
return absl::strings_internal::SingleArgStrAppend(*result, i);
}
// This overload is only selected if all the parameters are numbers that can be
// handled quickly.
// Later we can look into how we can extend this to more general argument
// mixtures without bloating codegen too much, or copying unnecessarily.
template <typename String, typename... T>
std::enable_if_t<
(sizeof...(T) > 1),
std::common_type_t<std::conditional_t<
true, void, absl::strings_internal::EnableIfFastCase<T>>...>>
StrAppend(absl::Nonnull<String*> str, T... args) {
// Do not add unnecessary variables, logic, or even "free" lambdas here.
// They can add overhead for the compiler and/or at run time.
// Furthermore, assume this function will be inlined.
// This function is carefully tailored to be able to be largely optimized away
// so that it becomes near-equivalent to the caller handling each argument
// individually while minimizing register pressure, so that the compiler
// can inline it with minimal overhead.
// First, calculate the total length, so we can perform just a single resize.
// Save all the lengths for later.
size_t total_length = 0;
const ptrdiff_t lengths[] = {
absl::numbers_internal::GetNumDigitsOrNegativeIfNegative(args)...};
for (const ptrdiff_t possibly_negative_length : lengths) {
// Lengths are negative for negative numbers. Keep them for later use, but
// take their absolute values for calculating total lengths;
total_length += possibly_negative_length < 0
? static_cast<size_t>(-possibly_negative_length)
: static_cast<size_t>(possibly_negative_length);
}
// Now reserve space for all the arguments.
const size_t old_size = str->size();
absl::strings_internal::STLStringAppendUninitializedAmortized(str,
total_length);
// Finally, output each argument one-by-one, from left to right.
size_t i = 0; // The current argument we're processing
ptrdiff_t n; // The length of the current argument
typename String::pointer pos = &(*str)[old_size];
using SomeTrivialEmptyType = std::false_type;
// Ugly code due to the lack of C++14 fold expression makes us.
const SomeTrivialEmptyType dummy1;
for (const SomeTrivialEmptyType& dummy2 :
{(/* Comma expressions are poor man's C++17 fold expression for C++14 */
(void)(n = lengths[i]),
(void)(n < 0 ? (void)(*pos++ = '-'), (n = ~n) : 0),
(void)absl::numbers_internal::FastIntToBufferBackward(
absl::numbers_internal::UnsignedAbsoluteValue(std::move(args)),
pos += n, static_cast<uint32_t>(n)),
(void)++i, dummy1)...}) {
(void)dummy2; // Remove & migrate to fold expressions in C++17
}
}
// Helper function for the future StrCat default floating-point format, %.6g
// This is fast.
inline strings_internal::AlphaNumBuffer<
numbers_internal::kSixDigitsToBufferSize>
SixDigits(double d) {
strings_internal::AlphaNumBuffer<numbers_internal::kSixDigitsToBufferSize>
result;
result.size = numbers_internal::SixDigitsToBuffer(d, &result.data[0]);
return result;
}
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_STRINGS_STR_CAT_H_