223 lines · c
1//===-- Standalone implementation std::string_view --------------*- 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-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef LLVM_LIBC_SRC___SUPPORT_CPP_STRING_VIEW_H10#define LLVM_LIBC_SRC___SUPPORT_CPP_STRING_VIEW_H11 12#include "limits.h"13#include "src/__support/common.h"14#include "src/__support/macros/config.h"15 16#include <stddef.h>17 18namespace LIBC_NAMESPACE_DECL {19namespace cpp {20 21// This is very simple alternate of the std::string_view class. There is no22// bounds check performed in any of the methods. The callers are expected to23// do the checks before invoking the methods.24//25// This class will be extended as needed in future.26class string_view {27private:28 const char *Data;29 size_t Len;30 31 LIBC_INLINE static size_t min(size_t A, size_t B) { return A <= B ? A : B; }32 33 LIBC_INLINE static int compareMemory(const char *Lhs, const char *Rhs,34 size_t Length) {35 for (size_t i = 0; i < Length; ++i)36 if (int Diff = (int)Lhs[i] - (int)Rhs[i])37 return Diff;38 return 0;39 }40 41 LIBC_INLINE static constexpr size_t length(const char *Str) {42 for (const char *End = Str;; ++End)43 if (*End == '\0')44 return static_cast<size_t>(End - Str);45 }46 47 LIBC_INLINE bool equals(string_view Other) const {48 return (Len == Other.Len &&49 compareMemory(Data, Other.Data, Other.Len) == 0);50 }51 52public:53 using value_type = char;54 using size_type = size_t;55 using difference_type = ptrdiff_t;56 using pointer = char *;57 using const_pointer = const char *;58 using reference = char &;59 using const_reference = const char &;60 using const_iterator = char *;61 using iterator = const_iterator;62 63 // special value equal to the maximum value representable by the type64 // size_type.65 LIBC_INLINE_VAR static constexpr size_t npos =66 cpp::numeric_limits<size_t>::max();67 68 LIBC_INLINE constexpr string_view() : Data(nullptr), Len(0) {}69 70 // Assumes Str is a null-terminated string. The length of the string does71 // not include the terminating null character.72 // Preconditions: [Str, Str + length(Str)) is a valid range.73 LIBC_INLINE constexpr string_view(const char *Str)74 : Data(Str), Len(length(Str)) {}75 76 // Preconditions: [Str, Str + N) is a valid range.77 LIBC_INLINE constexpr string_view(const char *Str, size_t N)78 : Data(Str), Len(N) {}79 80 LIBC_INLINE constexpr const char *data() const { return Data; }81 82 // Returns the size of the string_view.83 LIBC_INLINE constexpr size_t size() const { return Len; }84 85 // Returns whether the string_view is empty.86 LIBC_INLINE constexpr bool empty() const { return Len == 0; }87 88 // Returns an iterator to the first character of the view.89 LIBC_INLINE const char *begin() const { return Data; }90 91 // Returns an iterator to the character following the last character of the92 // view.93 LIBC_INLINE const char *end() const { return Data + Len; }94 95 // Returns a const reference to the character at specified location pos.96 // No bounds checking is performed: the behavior is undefined if pos >=97 // size().98 LIBC_INLINE constexpr const char &operator[](size_t Index) const {99 return Data[Index];100 }101 102 /// compare - Compare two strings; the result is -1, 0, or 1 if this string103 /// is lexicographically less than, equal to, or greater than the \p Other.104 LIBC_INLINE int compare(string_view Other) const {105 // Check the prefix for a mismatch.106 if (int Res = compareMemory(Data, Other.Data, min(Len, Other.Len)))107 return Res < 0 ? -1 : 1;108 // Otherwise the prefixes match, so we only need to check the lengths.109 if (Len == Other.Len)110 return 0;111 return Len < Other.Len ? -1 : 1;112 }113 114 LIBC_INLINE bool operator==(string_view Other) const { return equals(Other); }115 LIBC_INLINE bool operator!=(string_view Other) const {116 return !(*this == Other);117 }118 LIBC_INLINE bool operator<(string_view Other) const {119 return compare(Other) == -1;120 }121 LIBC_INLINE bool operator<=(string_view Other) const {122 return compare(Other) != 1;123 }124 LIBC_INLINE bool operator>(string_view Other) const {125 return compare(Other) == 1;126 }127 LIBC_INLINE bool operator>=(string_view Other) const {128 return compare(Other) != -1;129 }130 131 // Moves the start of the view forward by n characters.132 // The behavior is undefined if n > size().133 LIBC_INLINE void remove_prefix(size_t N) {134 Len -= N;135 Data += N;136 }137 138 // Moves the end of the view back by n characters.139 // The behavior is undefined if n > size().140 LIBC_INLINE void remove_suffix(size_t N) { Len -= N; }141 142 // Check if this string starts with the given Prefix.143 LIBC_INLINE bool starts_with(string_view Prefix) const {144 return Len >= Prefix.Len &&145 compareMemory(Data, Prefix.Data, Prefix.Len) == 0;146 }147 148 // Check if this string starts with the given Prefix.149 LIBC_INLINE bool starts_with(const char Prefix) const {150 return !empty() && front() == Prefix;151 }152 153 // Check if this string ends with the given Prefix.154 LIBC_INLINE bool ends_with(const char Suffix) const {155 return !empty() && back() == Suffix;156 }157 158 // Check if this string ends with the given Suffix.159 LIBC_INLINE bool ends_with(string_view Suffix) const {160 return Len >= Suffix.Len &&161 compareMemory(end() - Suffix.Len, Suffix.Data, Suffix.Len) == 0;162 }163 164 // Return a reference to the substring from [Start, Start + N).165 //166 // Start The index of the starting character in the substring; if the index is167 // npos or greater than the length of the string then the empty substring will168 // be returned.169 //170 // N The number of characters to included in the substring. If N exceeds the171 // number of characters remaining in the string, the string suffix (starting172 // with Start) will be returned.173 LIBC_INLINE string_view substr(size_t Start, size_t N = npos) const {174 Start = min(Start, Len);175 return string_view(Data + Start, min(N, Len - Start));176 }177 178 // front - Get the first character in the string.179 LIBC_INLINE char front() const { return Data[0]; }180 181 // back - Get the last character in the string.182 LIBC_INLINE char back() const { return Data[Len - 1]; }183 184 // Finds the first occurence of c in this view, starting at position From.185 LIBC_INLINE constexpr size_t find_first_of(const char c,186 size_t From = 0) const {187 for (size_t Pos = From; Pos < size(); ++Pos)188 if ((*this)[Pos] == c)189 return Pos;190 return npos;191 }192 193 // Finds the last occurence of c in this view, ending at position End.194 LIBC_INLINE constexpr size_t find_last_of(const char c,195 size_t End = npos) const {196 End = End >= size() ? size() : End + 1;197 for (; End > 0; --End)198 if ((*this)[End - 1] == c)199 return End - 1;200 return npos;201 }202 203 // Finds the first character not equal to c in this view, starting at position204 // From.205 LIBC_INLINE constexpr size_t find_first_not_of(const char c,206 size_t From = 0) const {207 for (size_t Pos = From; Pos < size(); ++Pos)208 if ((*this)[Pos] != c)209 return Pos;210 return npos;211 }212 213 // Check if this view contains the given character.214 LIBC_INLINE constexpr bool contains(char c) const {215 return find_first_of(c) != npos;216 }217};218 219} // namespace cpp220} // namespace LIBC_NAMESPACE_DECL221 222#endif // LLVM_LIBC_SRC___SUPPORT_CPP_STRING_VIEW_H223