summaryrefslogtreecommitdiff
path: root/absl/strings/str_cat.cc
blob: 99eb28908c192f8035fe490745fd5f6d8c674635 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
// 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
//
//      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.

#include "absl/strings/str_cat.h"

#include <assert.h>
#include <algorithm>
#include <cstdint>
#include <cstring>

#include "absl/strings/ascii.h"
#include "absl/strings/internal/resize_uninitialized.h"

namespace absl {

AlphaNum::AlphaNum(Hex hex) {
  char* const end = &digits_[numbers_internal::kFastToBufferSize];
  char* writer = end;
  uint64_t value = hex.value;
  static const char hexdigits[] = "0123456789abcdef";
  do {
    *--writer = hexdigits[value & 0xF];
    value >>= 4;
  } while (value != 0);

  char* beg;
  if (end - writer < hex.width) {
    beg = end - hex.width;
    std::fill_n(beg, writer - beg, hex.fill);
  } else {
    beg = writer;
  }

  piece_ = absl::string_view(beg, end - beg);
}

// ----------------------------------------------------------------------
// StrCat()
//    This merges the given strings or integers, with no delimiter.  This
//    is designed to be the fastest possible way to construct a std::string out
//    of a mix of raw C strings, StringPieces, 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();
  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.begin();
  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.begin();
  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.begin();
  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 {

// 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 (const absl::string_view piece : pieces) total_size += piece.size();
  strings_internal::STLStringResizeUninitialized(&result, total_size);

  char* const begin = &*result.begin();
  char* out = begin;
  for (const absl::string_view piece : pieces) {
    const size_t this_size = piece.size();
    memcpy(out, piece.data(), this_size);
    out += this_size;
  }
  assert(out == begin + result.size());
  return result;
}

// It's possible to call StrAppend with an absl::string_view that is itself a
// fragment of the std::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 std::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 (const absl::string_view piece : pieces) {
    ASSERT_NO_OVERLAP(*dest, piece);
    total_size += piece.size();
  }
  strings_internal::STLStringResizeUninitialized(dest, total_size);

  char* const begin = &*dest->begin();
  char* out = begin + old_size;
  for (const absl::string_view piece : pieces) {
    const size_t this_size = piece.size();
    memcpy(out, piece.data(), this_size);
    out += this_size;
  }
  assert(out == begin + dest->size());
}

}  // namespace strings_internal

void StrAppend(std::string* dest, const AlphaNum& a) {
  ASSERT_NO_OVERLAP(*dest, a);
  dest->append(a.data(), a.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::STLStringResizeUninitialized(
      dest, old_size + a.size() + b.size());
  char* const begin = &*dest->begin();
  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::STLStringResizeUninitialized(
      dest, old_size + a.size() + b.size() + c.size());
  char* const begin = &*dest->begin();
  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::STLStringResizeUninitialized(
      dest, old_size + a.size() + b.size() + c.size() + d.size());
  char* const begin = &*dest->begin();
  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());
}

}  // namespace absl