Encoding.h revision 341825 
1//===--- Encoding.h - Format C++ code ---------------------------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9///
10/// \file
11/// Contains functions for text encoding manipulation. Supports UTF-8,
12/// 8-bit encodings and escape sequences in C++ string literals.
13///
14//===----------------------------------------------------------------------===//
15
16#ifndef LLVM_CLANG_LIB_FORMAT_ENCODING_H
17#define LLVM_CLANG_LIB_FORMAT_ENCODING_H
18
19#include "clang/Basic/LLVM.h"
20#include "llvm/ADT/StringRef.h"
21#include "llvm/Support/ConvertUTF.h"
22#include "llvm/Support/Unicode.h"
23
24namespace clang {
25namespace format {
26namespace encoding {
27
28enum Encoding {
29  Encoding_UTF8,
30  Encoding_Unknown // We treat all other encodings as 8-bit encodings.
31};
32
33/// Detects encoding of the Text. If the Text can be decoded using UTF-8,
34/// it is considered UTF8, otherwise we treat it as some 8-bit encoding.
35inline Encoding detectEncoding(StringRef Text) {
36  const llvm::UTF8 *Ptr = reinterpret_cast<const llvm::UTF8 *>(Text.begin());
37  const llvm::UTF8 *BufEnd = reinterpret_cast<const llvm::UTF8 *>(Text.end());
38  if (llvm::isLegalUTF8String(&Ptr, BufEnd))
39    return Encoding_UTF8;
40  return Encoding_Unknown;
41}
42
43/// Returns the number of columns required to display the \p Text on a
44/// generic Unicode-capable terminal. Text is assumed to use the specified
45/// \p Encoding.
46inline unsigned columnWidth(StringRef Text, Encoding Encoding) {
47  if (Encoding == Encoding_UTF8) {
48    int ContentWidth = llvm::sys::unicode::columnWidthUTF8(Text);
49    // FIXME: Figure out the correct way to handle this in the presence of both
50    // printable and unprintable multi-byte UTF-8 characters. Falling back to
51    // returning the number of bytes may cause problems, as columnWidth suddenly
52    // becomes non-additive.
53    if (ContentWidth >= 0)
54      return ContentWidth;
55  }
56  return Text.size();
57}
58
59/// Returns the number of columns required to display the \p Text,
60/// starting from the \p StartColumn on a terminal with the \p TabWidth. The
61/// text is assumed to use the specified \p Encoding.
62inline unsigned columnWidthWithTabs(StringRef Text, unsigned StartColumn,
63                                    unsigned TabWidth, Encoding Encoding) {
64  unsigned TotalWidth = 0;
65  StringRef Tail = Text;
66  for (;;) {
67    StringRef::size_type TabPos = Tail.find('\t');
68    if (TabPos == StringRef::npos)
69      return TotalWidth + columnWidth(Tail, Encoding);
70    TotalWidth += columnWidth(Tail.substr(0, TabPos), Encoding);
71    TotalWidth += TabWidth - (TotalWidth + StartColumn) % TabWidth;
72    Tail = Tail.substr(TabPos + 1);
73  }
74}
75
76/// Gets the number of bytes in a sequence representing a single
77/// codepoint and starting with FirstChar in the specified Encoding.
78inline unsigned getCodePointNumBytes(char FirstChar, Encoding Encoding) {
79  switch (Encoding) {
80  case Encoding_UTF8:
81    return llvm::getNumBytesForUTF8(FirstChar);
82  default:
83    return 1;
84  }
85}
86
87inline bool isOctDigit(char c) { return '0' <= c && c <= '7'; }
88
89inline bool isHexDigit(char c) {
90  return ('0' <= c && c <= '9') || ('a' <= c && c <= 'f') ||
91         ('A' <= c && c <= 'F');
92}
93
94/// Gets the length of an escape sequence inside a C++ string literal.
95/// Text should span from the beginning of the escape sequence (starting with a
96/// backslash) to the end of the string literal.
97inline unsigned getEscapeSequenceLength(StringRef Text) {
98  assert(Text[0] == '\\');
99  if (Text.size() < 2)
100    return 1;
101
102  switch (Text[1]) {
103  case 'u':
104    return 6;
105  case 'U':
106    return 10;
107  case 'x': {
108    unsigned I = 2; // Point after '\x'.
109    while (I < Text.size() && isHexDigit(Text[I]))
110      ++I;
111    return I;
112  }
113  default:
114    if (isOctDigit(Text[1])) {
115      unsigned I = 1;
116      while (I < Text.size() && I < 4 && isOctDigit(Text[I]))
117        ++I;
118      return I;
119    }
120    return 1 + llvm::getNumBytesForUTF8(Text[1]);
121  }
122}
123
124} // namespace encoding
125} // namespace format
126} // namespace clang
127
128#endif
129