1 //===--- StringView.h -------------------------------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // FIXME: Use std::string_view instead when we support C++17.
10 // There are two copies of this file in the source tree.  The one under
11 // libcxxabi is the original and the one under llvm is the copy.  Use
12 // cp-to-llvm.sh to update the copy.  See README.txt for more details.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #ifndef DEMANGLE_STRINGVIEW_H
17 #define DEMANGLE_STRINGVIEW_H
18 
19 #include "DemangleConfig.h"
20 #include <cassert>
21 #include <cstring>
22 
23 DEMANGLE_NAMESPACE_BEGIN
24 
25 class StringView {
26   const char *First;
27   const char *Last;
28 
29 public:
30   static const size_t npos = ~size_t(0);
31 
32   template <size_t N>
33   StringView(const char (&Str)[N]) : First(Str), Last(Str + N - 1) {}
34   StringView(const char *First_, const char *Last_)
35       : First(First_), Last(Last_) {}
36   StringView(const char *First_, size_t Len)
37       : First(First_), Last(First_ + Len) {}
38   StringView(const char *Str) : First(Str), Last(Str + std::strlen(Str)) {}
39   StringView() : First(nullptr), Last(nullptr) {}
40 
41   StringView substr(size_t Pos, size_t Len = npos) const {
42     assert(Pos <= size());
43     if (Len > size() - Pos)
44       Len = size() - Pos;
45     return StringView(begin() + Pos, Len);
46   }
47 
48   size_t find(char C, size_t From = 0) const {
49     // Avoid calling memchr with nullptr.
50     if (From < size()) {
51       // Just forward to memchr, which is faster than a hand-rolled loop.
52       if (const void *P = ::memchr(First + From, C, size() - From))
53         return size_t(static_cast<const char *>(P) - First);
54     }
55     return npos;
56   }
57 
58   StringView dropFront(size_t N = 1) const {
59     if (N >= size())
60       N = size();
61     return StringView(First + N, Last);
62   }
63 
64   StringView dropBack(size_t N = 1) const {
65     if (N >= size())
66       N = size();
67     return StringView(First, Last - N);
68   }
69 
70   char front() const {
71     assert(!empty());
72     return *begin();
73   }
74 
75   char back() const {
76     assert(!empty());
77     return *(end() - 1);
78   }
79 
80   char popFront() {
81     assert(!empty());
82     return *First++;
83   }
84 
85   bool consumeFront(char C) {
86     if (!startsWith(C))
87       return false;
88     *this = dropFront(1);
89     return true;
90   }
91 
92   bool consumeFront(StringView S) {
93     if (!startsWith(S))
94       return false;
95     *this = dropFront(S.size());
96     return true;
97   }
98 
99   bool startsWith(char C) const { return !empty() && *begin() == C; }
100 
101   bool startsWith(StringView Str) const {
102     if (Str.size() > size())
103       return false;
104     return std::strncmp(Str.begin(), begin(), Str.size()) == 0;
105   }
106 
107   const char &operator[](size_t Idx) const { return *(begin() + Idx); }
108 
109   const char *begin() const { return First; }
110   const char *end() const { return Last; }
111   size_t size() const { return static_cast<size_t>(Last - First); }
112   bool empty() const { return First == Last; }
113 };
114 
115 inline bool operator==(const StringView &LHS, const StringView &RHS) {
116   return LHS.size() == RHS.size() &&
117          std::strncmp(LHS.begin(), RHS.begin(), LHS.size()) == 0;
118 }
119 
120 DEMANGLE_NAMESPACE_END
121 
122 #endif
123