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      1 //===--- Encoding.h - Format C++ code -------------------------------------===//
      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 /// \brief 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_FORMAT_ENCODING_H
     17 #define LLVM_CLANG_FORMAT_ENCODING_H
     18 
     19 #include "clang/Basic/LLVM.h"
     20 #include "llvm/Support/ConvertUTF.h"
     21 #include "llvm/Support/Unicode.h"
     22 
     23 namespace clang {
     24 namespace format {
     25 namespace encoding {
     26 
     27 enum Encoding {
     28   Encoding_UTF8,
     29   Encoding_Unknown // We treat all other encodings as 8-bit encodings.
     30 };
     31 
     32 /// \brief Detects encoding of the Text. If the Text can be decoded using UTF-8,
     33 /// it is considered UTF8, otherwise we treat it as some 8-bit encoding.
     34 inline Encoding detectEncoding(StringRef Text) {
     35   const UTF8 *Ptr = reinterpret_cast<const UTF8 *>(Text.begin());
     36   const UTF8 *BufEnd = reinterpret_cast<const UTF8 *>(Text.end());
     37   if (::isLegalUTF8String(&Ptr, BufEnd))
     38     return Encoding_UTF8;
     39   return Encoding_Unknown;
     40 }
     41 
     42 inline unsigned getCodePointCountUTF8(StringRef Text) {
     43   unsigned CodePoints = 0;
     44   for (size_t i = 0, e = Text.size(); i < e; i += getNumBytesForUTF8(Text[i])) {
     45     ++CodePoints;
     46   }
     47   return CodePoints;
     48 }
     49 
     50 /// \brief Gets the number of code points in the Text using the specified
     51 /// Encoding.
     52 inline unsigned getCodePointCount(StringRef Text, Encoding Encoding) {
     53   switch (Encoding) {
     54   case Encoding_UTF8:
     55     return getCodePointCountUTF8(Text);
     56   default:
     57     return Text.size();
     58   }
     59 }
     60 
     61 /// \brief Returns the number of columns required to display the \p Text on a
     62 /// generic Unicode-capable terminal. Text is assumed to use the specified
     63 /// \p Encoding.
     64 inline unsigned columnWidth(StringRef Text, Encoding Encoding) {
     65   if (Encoding == Encoding_UTF8) {
     66     int ContentWidth = llvm::sys::unicode::columnWidthUTF8(Text);
     67     // FIXME: Figure out the correct way to handle this in the presence of both
     68     // printable and unprintable multi-byte UTF-8 characters. Falling back to
     69     // returning the number of bytes may cause problems, as columnWidth suddenly
     70     // becomes non-additive.
     71     if (ContentWidth >= 0)
     72       return ContentWidth;
     73   }
     74   return Text.size();
     75 }
     76 
     77 /// \brief Returns the number of columns required to display the \p Text,
     78 /// starting from the \p StartColumn on a terminal with the \p TabWidth. The
     79 /// text is assumed to use the specified \p Encoding.
     80 inline unsigned columnWidthWithTabs(StringRef Text, unsigned StartColumn,
     81                                     unsigned TabWidth, Encoding Encoding) {
     82   unsigned TotalWidth = 0;
     83   StringRef Tail = Text;
     84   for (;;) {
     85     StringRef::size_type TabPos = Tail.find('\t');
     86     if (TabPos == StringRef::npos)
     87       return TotalWidth + columnWidth(Tail, Encoding);
     88     TotalWidth += columnWidth(Tail.substr(0, TabPos), Encoding);
     89     TotalWidth += TabWidth - (TotalWidth + StartColumn) % TabWidth;
     90     Tail = Tail.substr(TabPos + 1);
     91   }
     92 }
     93 
     94 /// \brief Gets the number of bytes in a sequence representing a single
     95 /// codepoint and starting with FirstChar in the specified Encoding.
     96 inline unsigned getCodePointNumBytes(char FirstChar, Encoding Encoding) {
     97   switch (Encoding) {
     98   case Encoding_UTF8:
     99     return getNumBytesForUTF8(FirstChar);
    100   default:
    101     return 1;
    102   }
    103 }
    104 
    105 inline bool isOctDigit(char c) { return '0' <= c && c <= '7'; }
    106 
    107 inline bool isHexDigit(char c) {
    108   return ('0' <= c && c <= '9') || ('a' <= c && c <= 'f') ||
    109          ('A' <= c && c <= 'F');
    110 }
    111 
    112 /// \brief Gets the length of an escape sequence inside a C++ string literal.
    113 /// Text should span from the beginning of the escape sequence (starting with a
    114 /// backslash) to the end of the string literal.
    115 inline unsigned getEscapeSequenceLength(StringRef Text) {
    116   assert(Text[0] == '\\');
    117   if (Text.size() < 2)
    118     return 1;
    119 
    120   switch (Text[1]) {
    121   case 'u':
    122     return 6;
    123   case 'U':
    124     return 10;
    125   case 'x': {
    126     unsigned I = 2; // Point after '\x'.
    127     while (I < Text.size() && isHexDigit(Text[I]))
    128       ++I;
    129     return I;
    130   }
    131   default:
    132     if (isOctDigit(Text[1])) {
    133       unsigned I = 1;
    134       while (I < Text.size() && I < 4 && isOctDigit(Text[I]))
    135         ++I;
    136       return I;
    137     }
    138     return 2;
    139   }
    140 }
    141 
    142 } // namespace encoding
    143 } // namespace format
    144 } // namespace clang
    145 
    146 #endif // LLVM_CLANG_FORMAT_ENCODING_H
    147