xpcom/string/nsASCIIMask.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef nsASCIIMask_h_
   8 #define nsASCIIMask_h_
   9
  10 #include <array>
  11 #include <utility>
  12
  13 #include "mozilla/Attributes.h"
  14
  15 typedef std::array<bool, 128> ASCIIMaskArray;
  16
  17 namespace mozilla {
  18
  19 // Boolean arrays, fixed size and filled in at compile time, meant to
  20 // record something about each of the (standard) ASCII characters.
  21 // No extended ASCII for now, there has been no use case.
  22 // If you have loops that go through a string character by character
  23 // and test for equality to a certain set of characters before deciding
  24 // on a course of action, chances are building up one of these arrays
  25 // and using it is going to be faster, especially if the set of
  26 // characters is more than one long, and known at compile time.
  27 class ASCIIMask {
  28  public:
  29   // Preset masks for some common character groups
  30   // When testing, you must check if the index is < 128 or use IsMasked()
  31   //
  32   // if (someChar < 128 && MaskCRLF()[someChar]) this is \r or \n
  33
  34   static const ASCIIMaskArray& MaskCRLF();
  35   static const ASCIIMaskArray& Mask0to9();
  36   static const ASCIIMaskArray& MaskCRLFTab();
  37   static const ASCIIMaskArray& MaskWhitespace();
  38
  39   static MOZ_ALWAYS_INLINE bool IsMasked(const ASCIIMaskArray& aMask,
  40                                          uint32_t aChar) {
  41     return aChar < 128 && aMask[aChar];
  42   }
  43 };
  44
  45 // Outside of the preset ones, use these templates to create more masks.
  46 //
  47 // The example creation will look like this:
  48 //
  49 // constexpr bool TestABC(char c) { return c == 'A' || c == 'B' || c == 'C'; }
  50 // constexpr std::array<bool, 128> sABCMask = CreateASCIIMask(TestABC);
  51 // ...
  52 // if (someChar < 128 && sABCMask[someChar]) this is A or B or C
  53
  54 namespace asciimask_details {
  55 template <typename F, size_t... Indices>
  56 constexpr std::array<bool, 128> CreateASCIIMask(
  57     F fun, std::index_sequence<Indices...>) {
  58   return {{fun(Indices)...}};
  59 }
  60 }  // namespace asciimask_details
  61
  62 template <typename F>
  63 constexpr std::array<bool, 128> CreateASCIIMask(F fun) {
  64   return asciimask_details::CreateASCIIMask(fun,
  65                                             std::make_index_sequence<128>{});
  66 }
  67
  68 }  // namespace mozilla
  69
  70 #endif  // nsASCIIMask_h_