blob: fe01c53c4c06295bde42affce88d2847bcbe7b6f [file] [log] [blame]
// 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.
#include <stddef.h>
#include <string>
#include "base/compiler_specific.h"
namespace gurl_base {
// constexpr version of
// 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;
// Searches for character |c| within the first |n| characters of the sequence
// pointed to by |s|.
static constexpr const T* find(const T* s, size_t n, T c);
template <typename T>
constexpr int CharTraits<T>::compare(const T* s1,
const T* s2,
size_t n) noexcept {
// Comparison with operator < fails, because of signed/unsigned
// mismatch,
// std::char_traits<T>::lt is guaranteed to be constexpr in C++14:
for (; n; --n, ++s1, ++s2) {
if (std::char_traits<T>::lt(*s1, *s2))
return -1;
if (std::char_traits<T>::lt(*s2, *s1))
return 1;
return 0;
template <typename T>
constexpr size_t CharTraits<T>::length(const T* s) noexcept {
size_t i = 0;
for (; *s; ++s)
return i;
template <typename T>
constexpr const T* CharTraits<T>::find(const T* s, size_t n, T c) {
for (; n; --n, ++s) {
if (std::char_traits<T>::eq(*s, c))
return s;
return nullptr;
// char and wchar_t specialization of CharTraits that can use clang's constexpr
// instrinsics, where available.
#if HAS_FEATURE(cxx_constexpr_string_builtins)
template <>
struct CharTraits<char> {
static constexpr int compare(const char* s1,
const char* s2,
size_t n) noexcept {
return __builtin_memcmp(s1, s2, n);
static constexpr size_t length(const char* s) noexcept {
return __builtin_strlen(s);
static constexpr const char* find(const char* s, size_t n, char c) {
return __builtin_char_memchr(s, c, n);
template <>
struct CharTraits<wchar_t> {
static constexpr int compare(const wchar_t* s1,
const wchar_t* s2,
size_t n) noexcept {
return __builtin_wmemcmp(s1, s2, n);
static constexpr size_t length(const wchar_t* s) noexcept {
return __builtin_wcslen(s);
static constexpr const wchar_t* find(const wchar_t* s, size_t n, wchar_t c) {
return __builtin_wmemchr(s, c, n);
} // namespace base