93 lines
2.5 KiB
C++
93 lines
2.5 KiB
C++
// Copyright 2018 The Chromium Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style license that can be
|
|
// found in the LICENSE file.
|
|
|
|
#ifndef BASE_STRINGS_CHAR_TRAITS_H_
|
|
#define BASE_STRINGS_CHAR_TRAITS_H_
|
|
|
|
#include <stddef.h>
|
|
|
|
#include "base/compiler_specific.h"
|
|
|
|
namespace base {
|
|
|
|
// constexpr version of http://en.cppreference.com/w/cpp/string/char_traits.
|
|
// This currently just implements the bits needed to support a (mostly)
|
|
// constexpr StringPiece.
|
|
//
|
|
// TODO(dcheng): Once we switch to C++17, most methods will become constexpr and
|
|
// we can switch over to using the one in the standard library.
|
|
template <typename T>
|
|
struct CharTraits {
|
|
// Performs a lexographical comparison of the first N characters of |s1| and
|
|
// |s2|. Returns 0 if equal, -1 if |s1| is less than |s2|, and 1 if |s1| is
|
|
// greater than |s2|.
|
|
static constexpr int compare(const T* s1, const T* s2, size_t n) noexcept;
|
|
|
|
// Returns the length of |s|, assuming null termination (and not including the
|
|
// terminating null).
|
|
static constexpr size_t length(const T* s) noexcept;
|
|
};
|
|
|
|
template <typename T>
|
|
constexpr int CharTraits<T>::compare(const T* s1,
|
|
const T* s2,
|
|
size_t n) noexcept {
|
|
for (; n; --n, ++s1, ++s2) {
|
|
if (*s1 < *s2)
|
|
return -1;
|
|
if (*s1 > *s2)
|
|
return 1;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
template <typename T>
|
|
constexpr size_t CharTraits<T>::length(const T* s) noexcept {
|
|
size_t i = 0;
|
|
for (; *s; ++s)
|
|
++i;
|
|
return i;
|
|
}
|
|
|
|
// char specialization of CharTraits that can use clang's constexpr instrinsics,
|
|
// where available.
|
|
template <>
|
|
struct CharTraits<char> {
|
|
static constexpr int compare(const char* s1,
|
|
const char* s2,
|
|
size_t n) noexcept;
|
|
static constexpr size_t length(const char* s) noexcept;
|
|
};
|
|
|
|
constexpr int CharTraits<char>::compare(const char* s1,
|
|
const char* s2,
|
|
size_t n) noexcept {
|
|
#if HAS_FEATURE(cxx_constexpr_string_builtins)
|
|
return __builtin_memcmp(s1, s2, n);
|
|
#else
|
|
for (; n; --n, ++s1, ++s2) {
|
|
if (*s1 < *s2)
|
|
return -1;
|
|
if (*s1 > *s2)
|
|
return 1;
|
|
}
|
|
return 0;
|
|
#endif
|
|
}
|
|
|
|
constexpr size_t CharTraits<char>::length(const char* s) noexcept {
|
|
#if defined(__clang__)
|
|
return __builtin_strlen(s);
|
|
#else
|
|
size_t i = 0;
|
|
for (; *s; ++s)
|
|
++i;
|
|
return i;
|
|
#endif
|
|
}
|
|
|
|
} // namespace base
|
|
|
|
#endif // BASE_STRINGS_CHAR_TRAITS_H_
|