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// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_STRINGS_STRING_UTIL_INTERNAL_H_
#define BASE_STRINGS_STRING_UTIL_INTERNAL_H_
#include <algorithm>
#include <concepts>
#include <string_view>
#include <type_traits>
namespace base::internal {
// ASCII-specific tolower. The standard library's tolower is locale sensitive,
// so we don't want to use it here.
template <typename CharT>
requires(std::integral<CharT>)
constexpr CharT ToLowerASCII(CharT c) {
return (c >= 'A' && c <= 'Z') ? (c + ('a' - 'A')) : c;
}
template <typename T>
requires(std::integral<typename T::value_type>)
constexpr int CompareCaseInsensitiveASCIIT(T a, T b) {
// Find the first characters that aren't equal and compare them. If the end
// of one of the strings is found before a nonequal character, the lengths
// of the strings are compared. Compare using the unsigned type so the sort
// order is independent of the signedness of `char`.
using UCharT = std::make_unsigned_t<typename T::value_type>;
size_t i = 0;
while (i < a.length() && i < b.length()) {
UCharT lower_a = static_cast<UCharT>(ToLowerASCII(a[i]));
UCharT lower_b = static_cast<UCharT>(ToLowerASCII(b[i]));
if (lower_a < lower_b) {
return -1;
}
if (lower_a > lower_b) {
return 1;
}
i++;
}
// End of one string hit before finding a different character. Expect the
// common case to be "strings equal" at this point so check that first.
if (a.length() == b.length()) {
return 0;
}
if (a.length() < b.length()) {
return -1;
}
return 1;
}
template <typename CharT, typename CharU>
inline bool EqualsCaseInsensitiveASCIIT(std::basic_string_view<CharT> a,
std::basic_string_view<CharU> b) {
return std::ranges::equal(a, b, [](auto lhs, auto rhs) {
return ToLowerASCII(lhs) == ToLowerASCII(rhs);
});
}
} // namespace base::internal
#endif // BASE_STRINGS_STRING_UTIL_INTERNAL_H_
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