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/**
* Copyright (C) 2020-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
/**
* Replacements for <cctype> or <ctype.h> functions and macros.
* These should be used instead of the corresponding standard functions.
* Note the camel-case spelling to distinguish these from the C++ functions
* and especially the C macros.
*
* Regarding the capitalization of these functions: POSIX defines standard
* identifiers for the 12 character classes. Each "is"- function here directly
* references and evokes such a POSIX identifier, so they are not
* camel-cased as ordinary English phrases (so `isAlnum` not `isAlNum`).
*
* <https://en.wikipedia.org/wiki/Regular_expression#Character_classes>
*
* Problems with the standard functions:
*
* - They accept int (to accept the EOF of -1 and integrate with cstdio).
* Passing negative char values other than EOF is undefined behavior!
* They cannot be used directly in std algorithms operating on char
* arguments because of this, say to `std::transform` or `std::find_if`
* on a `std::string`. You need a lambda and it has to do a cast.
* - Most are locale dependent, so they have to be slow. Dropping
* locale makes the "is"- functions 200% faster.
* - They return int instead of bool for C compatibility. Undesirable in C++.
* - In C they are macros, so they are very different entities depending on
* the subtle choice of #include <cctype> vs #include <ctype.h>.
* - Support for the EOF value bloats the lookup tables and carves out a
* surprising special case.
*
* The `<cctype>` character classification functions are a subtle source of bugs.
* See warnings at <https://en.cppreference.com/w/cpp/header/cctype>.
*
* The proper call sequence is often not done, creating bugs. So
* here are some more suitable C++17 implementations. We can make our versions
* constexpr and noexcept because they don't depend on the locale or other
* dynamic program state.
*/
#pragma once
#include <array>
#include <cstdint>
namespace mongo::ctype {
namespace detail {
/** Define a bit position for each character class queryable with this API. */
enum ClassBit : uint16_t {
kUpper = 1 << 0, //< [upper] UPPERCASE
kLower = 1 << 1, //< [lower] lowercase
kAlpha = 1 << 2, //< [alpha] Alphabetic (upper case or lower case)
kDigit = 1 << 3, //< [digit] Decimal digit
kXdigit = 1 << 4, //< [xdigit] Hexadecimal digit (upper case or lower case: [0-9A-Fa-f])
kSpace = 1 << 5, //< [space] Whitespace ([ \t\r\n\f\v])
kPrint = 1 << 6, //< [print] Printing (non-control chars)
kGraph = 1 << 7, //< [graph] Graphical (non-control, non-whitespace)
kBlank = 1 << 8, //< [blank] Blank (' ', '\t')
kCntrl = 1 << 9, //< [cntrl] Control character: 0x00-0x1f, and 0x7f (DEL)
kPunct = 1 << 10, //< [punct] Punctuation (graphical, but not alphanumeric)
kAlnum = 1 << 11 //< [alnum] Alphanumeric (letter or digit)
};
/** Returns the bitwise-or of all `ClassBit` pertinent to character `c`. */
constexpr uint16_t calculateClassBits(unsigned char c) {
if (c >= 0x80)
return 0;
uint16_t r = 0;
if (c <= 0x1f || c == 0x7f)
r |= kCntrl;
if (!(r & kCntrl))
r |= kPrint;
if (c == '\t' || c == ' ')
r |= kBlank;
if ((r & kBlank) || c == '\n' || c == '\v' || c == '\f' || c == '\r')
r |= kSpace;
if (c >= 'A' && c <= 'Z')
r |= kUpper;
if (c >= 'a' && c <= 'z')
r |= kLower;
if (c >= '0' && c <= '9')
r |= kDigit;
if ((r & kUpper) || (r & kLower))
r |= kAlpha;
if ((r & kDigit) || (c >= 'A' && c <= 'F') || (c >= 'a' && c <= 'f'))
r |= kXdigit;
if ((r & kAlpha) || (r & kDigit))
r |= kAlnum;
if ((r & kPrint) && !(r & kSpace))
r |= kGraph;
if ((r & kGraph) && !(r & kAlnum))
r |= kPunct;
return r;
}
/** The character class memberships for each char. */
constexpr auto chClassTable = [] {
std::array<uint16_t, 256> arr{};
for (size_t i = 0; i < arr.size(); ++i)
arr[i] = calculateClassBits(i);
return arr;
}();
constexpr bool isMember(char c, uint16_t mask) {
return chClassTable[static_cast<unsigned char>(c)] & mask;
}
/** Lookup table for `toUpper`. */
constexpr auto chUpperTable = [] {
std::array<char, 256> arr{};
for (size_t i = 0; i < arr.size(); ++i)
arr[i] = isMember(i, kLower) ? 'A' + (i - 'a') : i;
return arr;
}();
/** Lookup table for `toLower`. */
constexpr auto chLowerTable = [] {
std::array<char, 256> arr{};
for (size_t i = 0; i < arr.size(); ++i)
arr[i] = isMember(i, kUpper) ? 'a' + (i - 'A') : i;
return arr;
}();
} // namespace detail
/**
* These 12 "is"- functions exactly match the <cctype> definitions for the
* POSIX (or C) locale. See the corresponding definitions in <cctype>.
* <https://en.cppreference.com/w/cpp/header/cctype>
* See notes above.
*/
constexpr bool isAlnum(char c) noexcept {
return detail::isMember(c, detail::kAlnum);
}
constexpr bool isAlpha(char c) noexcept {
return detail::isMember(c, detail::kAlpha);
}
constexpr bool isLower(char c) noexcept {
return detail::isMember(c, detail::kLower);
}
constexpr bool isUpper(char c) noexcept {
return detail::isMember(c, detail::kUpper);
}
constexpr bool isDigit(char c) noexcept {
return detail::isMember(c, detail::kDigit);
}
constexpr bool isXdigit(char c) noexcept {
return detail::isMember(c, detail::kXdigit);
}
constexpr bool isCntrl(char c) noexcept {
return detail::isMember(c, detail::kCntrl);
}
constexpr bool isGraph(char c) noexcept {
return detail::isMember(c, detail::kGraph);
}
constexpr bool isSpace(char c) noexcept {
return detail::isMember(c, detail::kSpace);
}
constexpr bool isBlank(char c) noexcept {
return detail::isMember(c, detail::kBlank);
}
constexpr bool isPrint(char c) noexcept {
return detail::isMember(c, detail::kPrint);
}
constexpr bool isPunct(char c) noexcept {
return detail::isMember(c, detail::kPunct);
}
/**
* Returns the upper case of `c` if `c` is lower case, otherwise `c`.
* Unlike `std::toupper`, is not affected by locale. See notes above.
*/
constexpr char toUpper(char c) noexcept {
return detail::chUpperTable[static_cast<unsigned char>(c)];
}
/**
* Returns the lower case of `c` if `c` is upper case, otherwise `c`.
* Unlike `std::tolower`, is not affected by locale. See notes above.
*/
constexpr char toLower(char c) noexcept {
return detail::chLowerTable[static_cast<unsigned char>(c)];
}
} // namespace mongo::ctype
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