string_util_internal.h (2076B)
1 // Copyright 2020 The Chromium Authors 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef BASE_STRINGS_STRING_UTIL_INTERNAL_H_ 6 #define BASE_STRINGS_STRING_UTIL_INTERNAL_H_ 7 8 #include <type_traits> 9 10 #include "base/ranges/algorithm.h" 11 #include "base/strings/string_piece.h" 12 13 namespace base::internal { 14 15 // ASCII-specific tolower. The standard library's tolower is locale sensitive, 16 // so we don't want to use it here. 17 template <typename CharT, 18 typename = std::enable_if_t<std::is_integral_v<CharT>>> 19 constexpr CharT ToLowerASCII(CharT c) { 20 return (c >= 'A' && c <= 'Z') ? (c + ('a' - 'A')) : c; 21 } 22 23 template <typename T> 24 constexpr int CompareCaseInsensitiveASCIIT(T a, T b) { 25 // Find the first characters that aren't equal and compare them. If the end 26 // of one of the strings is found before a nonequal character, the lengths 27 // of the strings are compared. Compare using the unsigned type so the sort 28 // order is independent of the signedness of `char`. 29 static_assert(std::is_integral_v<typename T::value_type>); 30 using UCharT = std::make_unsigned_t<typename T::value_type>; 31 size_t i = 0; 32 while (i < a.length() && i < b.length()) { 33 UCharT lower_a = static_cast<UCharT>(ToLowerASCII(a[i])); 34 UCharT lower_b = static_cast<UCharT>(ToLowerASCII(b[i])); 35 if (lower_a < lower_b) 36 return -1; 37 if (lower_a > lower_b) 38 return 1; 39 i++; 40 } 41 42 // End of one string hit before finding a different character. Expect the 43 // common case to be "strings equal" at this point so check that first. 44 if (a.length() == b.length()) 45 return 0; 46 47 if (a.length() < b.length()) 48 return -1; 49 return 1; 50 } 51 52 template <typename CharT, typename CharU> 53 inline bool EqualsCaseInsensitiveASCIIT(BasicStringPiece<CharT> a, 54 BasicStringPiece<CharU> b) { 55 return ranges::equal(a, b, [](auto lhs, auto rhs) { 56 return ToLowerASCII(lhs) == ToLowerASCII(rhs); 57 }); 58 } 59 60 } // namespace base::internal 61 62 #endif // BASE_STRINGS_STRING_UTIL_INTERNAL_H_