mfbt/Range.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 mozilla_Range_h
   8 #define mozilla_Range_h
   9
  10 #include "mozilla/RangedPtr.h"
  11 #include "mozilla/Span.h"
  12
  13 #include <stddef.h>
  14 #include <type_traits>
  15
  16 namespace mozilla {
  17
  18 // Range<T> is a tuple containing a pointer and a length.
  19 template <typename T>
  20 class Range {
  21   template <typename U>
  22   friend class Range;
  23
  24   // Reassignment of RangedPtrs is so (subtly) restrictive that we just make
  25   // Range immutable.
  26   const RangedPtr<T> mStart;
  27   const RangedPtr<T> mEnd;
  28
  29  public:
  30   Range() : mStart(nullptr, 0), mEnd(nullptr, 0) {}
  31   Range(T* aPtr, size_t aLength)
  32       : mStart(aPtr, aPtr, aPtr + aLength),
  33         mEnd(aPtr + aLength, aPtr, aPtr + aLength) {
  34     if (!aPtr) {
  35       MOZ_ASSERT(!aLength,
  36                  "Range does not support nullptr with non-zero length.");
  37       // ...because merely having a pointer to `nullptr + 1` is undefined
  38       // behavior. UBSAN catches this as of clang-10.
  39     }
  40   }
  41   Range(const RangedPtr<T>& aStart, const RangedPtr<T>& aEnd)
  42       : mStart(aStart.get(), aStart.get(), aEnd.get()),
  43         mEnd(aEnd.get(), aStart.get(), aEnd.get()) {
  44     // Only accept two RangedPtrs within the same range.
  45     aStart.checkIdenticalRange(aEnd);
  46     MOZ_ASSERT(aStart <= aEnd);
  47   }
  48
  49   template <typename U, class = std::enable_if_t<
  50                             std::is_convertible_v<U (*)[], T (*)[]>, int>>
  51   MOZ_IMPLICIT Range(const Range<U>& aOther)
  52       : mStart(aOther.mStart), mEnd(aOther.mEnd) {}
  53
  54   MOZ_IMPLICIT Range(Span<T> aSpan) : Range(aSpan.Elements(), aSpan.Length()) {}
  55
  56   template <typename U, class = std::enable_if_t<
  57                             std::is_convertible_v<U (*)[], T (*)[]>, int>>
  58   MOZ_IMPLICIT Range(const Span<U>& aSpan)
  59       : Range(aSpan.Elements(), aSpan.Length()) {}
  60
  61   RangedPtr<T> begin() const { return mStart; }
  62   RangedPtr<T> end() const { return mEnd; }
  63   size_t length() const { return mEnd - mStart; }
  64
  65   T& operator[](size_t aOffset) const { return mStart[aOffset]; }
  66
  67   explicit operator bool() const { return mStart != nullptr; }
  68
  69   operator Span<T>() { return Span<T>(mStart.get(), length()); }
  70
  71   operator Span<const T>() const { return Span<T>(mStart.get(), length()); }
  72 };
  73
  74 template <typename T>
  75 Span(Range<T>&) -> Span<T>;
  76
  77 template <typename T>
  78 Span(const Range<T>&) -> Span<const T>;
  79
  80 }  // namespace mozilla
  81
  82 #endif /* mozilla_Range_h */