summaryrefslogtreecommitdiffstats
path: root/mfbt/CheckedInt.h
blob: a5e4f7ff1aaab99a3bba36dc845a6a906be97a18 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* Provides checked integers, detecting integer overflow and divide-by-0. */

#ifndef mozilla_CheckedInt_h
#define mozilla_CheckedInt_h

#include <stdint.h>
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/IntegerTypeTraits.h"

namespace mozilla {

template<typename T> class CheckedInt;

namespace detail {

/*
 * Step 1: manually record supported types
 *
 * What's nontrivial here is that there are different families of integer
 * types: basic integer types and stdint types. It is merrily undefined which
 * types from one family may be just typedefs for a type from another family.
 *
 * For example, on GCC 4.6, aside from the basic integer types, the only other
 * type that isn't just a typedef for some of them, is int8_t.
 */

struct UnsupportedType {};

template<typename IntegerType>
struct IsSupportedPass2
{
  static const bool value = false;
};

template<typename IntegerType>
struct IsSupported
{
  static const bool value = IsSupportedPass2<IntegerType>::value;
};

template<>
struct IsSupported<int8_t>
{ static const bool value = true; };

template<>
struct IsSupported<uint8_t>
{ static const bool value = true; };

template<>
struct IsSupported<int16_t>
{ static const bool value = true; };

template<>
struct IsSupported<uint16_t>
{ static const bool value = true; };

template<>
struct IsSupported<int32_t>
{ static const bool value = true; };

template<>
struct IsSupported<uint32_t>
{ static const bool value = true; };

template<>
struct IsSupported<int64_t>
{ static const bool value = true; };

template<>
struct IsSupported<uint64_t>
{ static const bool value = true; };


template<>
struct IsSupportedPass2<char>
{ static const bool value = true; };

template<>
struct IsSupportedPass2<signed char>
{ static const bool value = true; };

template<>
struct IsSupportedPass2<unsigned char>
{ static const bool value = true; };

template<>
struct IsSupportedPass2<short>
{ static const bool value = true; };

template<>
struct IsSupportedPass2<unsigned short>
{ static const bool value = true; };

template<>
struct IsSupportedPass2<int>
{ static const bool value = true; };

template<>
struct IsSupportedPass2<unsigned int>
{ static const bool value = true; };

template<>
struct IsSupportedPass2<long>
{ static const bool value = true; };

template<>
struct IsSupportedPass2<unsigned long>
{ static const bool value = true; };

template<>
struct IsSupportedPass2<long long>
{ static const bool value = true; };

template<>
struct IsSupportedPass2<unsigned long long>
{ static const bool value = true; };

/*
 * Step 2: Implement the actual validity checks.
 *
 * Ideas taken from IntegerLib, code different.
 */

template<typename IntegerType, size_t Size = sizeof(IntegerType)>
struct TwiceBiggerType
{
  typedef typename detail::StdintTypeForSizeAndSignedness<
                     sizeof(IntegerType) * 2,
                     IsSigned<IntegerType>::value
                   >::Type Type;
};

template<typename IntegerType>
struct TwiceBiggerType<IntegerType, 8>
{
  typedef UnsupportedType Type;
};

template<typename T>
inline bool
HasSignBit(T aX)
{
  // In C++, right bit shifts on negative values is undefined by the standard.
  // Notice that signed-to-unsigned conversions are always well-defined in the
  // standard, as the value congruent modulo 2**n as expected. By contrast,
  // unsigned-to-signed is only well-defined if the value is representable.
  return bool(typename MakeUnsigned<T>::Type(aX) >>
              PositionOfSignBit<T>::value);
}

// Bitwise ops may return a larger type, so it's good to use this inline
// helper guaranteeing that the result is really of type T.
template<typename T>
inline T
BinaryComplement(T aX)
{
  return ~aX;
}

template<typename T,
         typename U,
         bool IsTSigned = IsSigned<T>::value,
         bool IsUSigned = IsSigned<U>::value>
struct DoesRangeContainRange
{
};

template<typename T, typename U, bool Signedness>
struct DoesRangeContainRange<T, U, Signedness, Signedness>
{
  static const bool value = sizeof(T) >= sizeof(U);
};

template<typename T, typename U>
struct DoesRangeContainRange<T, U, true, false>
{
  static const bool value = sizeof(T) > sizeof(U);
};

template<typename T, typename U>
struct DoesRangeContainRange<T, U, false, true>
{
  static const bool value = false;
};

template<typename T,
         typename U,
         bool IsTSigned = IsSigned<T>::value,
         bool IsUSigned = IsSigned<U>::value,
         bool DoesTRangeContainURange = DoesRangeContainRange<T, U>::value>
struct IsInRangeImpl {};

template<typename T, typename U, bool IsTSigned, bool IsUSigned>
struct IsInRangeImpl<T, U, IsTSigned, IsUSigned, true>
{
  static bool run(U)
  {
    return true;
  }
};

template<typename T, typename U>
struct IsInRangeImpl<T, U, true, true, false>
{
  static bool run(U aX)
  {
    return aX <= MaxValue<T>::value && aX >= MinValue<T>::value;
  }
};

template<typename T, typename U>
struct IsInRangeImpl<T, U, false, false, false>
{
  static bool run(U aX)
  {
    return aX <= MaxValue<T>::value;
  }
};

template<typename T, typename U>
struct IsInRangeImpl<T, U, true, false, false>
{
  static bool run(U aX)
  {
    return sizeof(T) > sizeof(U) || aX <= U(MaxValue<T>::value);
  }
};

template<typename T, typename U>
struct IsInRangeImpl<T, U, false, true, false>
{
  static bool run(U aX)
  {
    return sizeof(T) >= sizeof(U)
           ? aX >= 0
           : aX >= 0 && aX <= U(MaxValue<T>::value);
  }
};

template<typename T, typename U>
inline bool
IsInRange(U aX)
{
  return IsInRangeImpl<T, U>::run(aX);
}

template<typename T>
inline bool
IsAddValid(T aX, T aY)
{
  // Addition is valid if the sign of aX+aY is equal to either that of aX or
  // that of aY. Since the value of aX+aY is undefined if we have a signed
  // type, we compute it using the unsigned type of the same size.  Beware!
  // These bitwise operations can return a larger integer type, if T was a
  // small type like int8_t, so we explicitly cast to T.

  typename MakeUnsigned<T>::Type ux = aX;
  typename MakeUnsigned<T>::Type uy = aY;
  typename MakeUnsigned<T>::Type result = ux + uy;
  return IsSigned<T>::value
         ? HasSignBit(BinaryComplement(T((result ^ aX) & (result ^ aY))))
         : BinaryComplement(aX) >= aY;
}

template<typename T>
inline bool
IsSubValid(T aX, T aY)
{
  // Subtraction is valid if either aX and aY have same sign, or aX-aY and aX
  // have same sign. Since the value of aX-aY is undefined if we have a signed
  // type, we compute it using the unsigned type of the same size.
  typename MakeUnsigned<T>::Type ux = aX;
  typename MakeUnsigned<T>::Type uy = aY;
  typename MakeUnsigned<T>::Type result = ux - uy;

  return IsSigned<T>::value
         ? HasSignBit(BinaryComplement(T((result ^ aX) & (aX ^ aY))))
         : aX >= aY;
}

template<typename T,
         bool IsTSigned = IsSigned<T>::value,
         bool TwiceBiggerTypeIsSupported =
           IsSupported<typename TwiceBiggerType<T>::Type>::value>
struct IsMulValidImpl {};

template<typename T, bool IsTSigned>
struct IsMulValidImpl<T, IsTSigned, true>
{
  static bool run(T aX, T aY)
  {
    typedef typename TwiceBiggerType<T>::Type TwiceBiggerType;
    TwiceBiggerType product = TwiceBiggerType(aX) * TwiceBiggerType(aY);
    return IsInRange<T>(product);
  }
};

template<typename T>
struct IsMulValidImpl<T, true, false>
{
  static bool run(T aX, T aY)
  {
    const T max = MaxValue<T>::value;
    const T min = MinValue<T>::value;

    if (aX == 0 || aY == 0) {
      return true;
    }
    if (aX > 0) {
      return aY > 0
             ? aX <= max / aY
             : aY >= min / aX;
    }

    // If we reach this point, we know that aX < 0.
    return aY > 0
           ? aX >= min / aY
           : aY >= max / aX;
  }
};

template<typename T>
struct IsMulValidImpl<T, false, false>
{
  static bool run(T aX, T aY)
  {
    return aY == 0 ||  aX <= MaxValue<T>::value / aY;
  }
};

template<typename T>
inline bool
IsMulValid(T aX, T aY)
{
  return IsMulValidImpl<T>::run(aX, aY);
}

template<typename T>
inline bool
IsDivValid(T aX, T aY)
{
  // Keep in mind that in the signed case, min/-1 is invalid because
  // abs(min)>max.
  return aY != 0 &&
         !(IsSigned<T>::value && aX == MinValue<T>::value && aY == T(-1));
}

template<typename T, bool IsTSigned = IsSigned<T>::value>
struct IsModValidImpl;

template<typename T>
inline bool
IsModValid(T aX, T aY)
{
  return IsModValidImpl<T>::run(aX, aY);
}

/*
 * Mod is pretty simple.
 * For now, let's just use the ANSI C definition:
 * If aX or aY are negative, the results are implementation defined.
 *   Consider these invalid.
 * Undefined for aY=0.
 * The result will never exceed either aX or aY.
 *
 * Checking that aX>=0 is a warning when T is unsigned.
 */

template<typename T>
struct IsModValidImpl<T, false>
{
  static inline bool run(T aX, T aY)
  {
    return aY >= 1;
  }
};

template<typename T>
struct IsModValidImpl<T, true>
{
  static inline bool run(T aX, T aY)
  {
    if (aX < 0) {
      return false;
    }
    return aY >= 1;
  }
};

template<typename T, bool IsSigned = IsSigned<T>::value>
struct NegateImpl;

template<typename T>
struct NegateImpl<T, false>
{
  static CheckedInt<T> negate(const CheckedInt<T>& aVal)
  {
    // Handle negation separately for signed/unsigned, for simpler code and to
    // avoid an MSVC warning negating an unsigned value.
    return CheckedInt<T>(0, aVal.isValid() && aVal.mValue == 0);
  }
};

template<typename T>
struct NegateImpl<T, true>
{
  static CheckedInt<T> negate(const CheckedInt<T>& aVal)
  {
    // Watch out for the min-value, which (with twos-complement) can't be
    // negated as -min-value is then (max-value + 1).
    if (!aVal.isValid() || aVal.mValue == MinValue<T>::value) {
      return CheckedInt<T>(aVal.mValue, false);
    }
    return CheckedInt<T>(-aVal.mValue, true);
  }
};

} // namespace detail


/*
 * Step 3: Now define the CheckedInt class.
 */

/**
 * @class CheckedInt
 * @brief Integer wrapper class checking for integer overflow and other errors
 * @param T the integer type to wrap. Can be any type among the following:
 *            - any basic integer type such as |int|
 *            - any stdint type such as |int8_t|
 *
 * This class implements guarded integer arithmetic. Do a computation, check
 * that isValid() returns true, you then have a guarantee that no problem, such
 * as integer overflow, happened during this computation, and you can call
 * value() to get the plain integer value.
 *
 * The arithmetic operators in this class are guaranteed not to raise a signal
 * (e.g. in case of a division by zero).
 *
 * For example, suppose that you want to implement a function that computes
 * (aX+aY)/aZ, that doesn't crash if aZ==0, and that reports on error (divide by
 * zero or integer overflow). You could code it as follows:
   @code
   bool computeXPlusYOverZ(int aX, int aY, int aZ, int* aResult)
   {
     CheckedInt<int> checkedResult = (CheckedInt<int>(aX) + aY) / aZ;
     if (checkedResult.isValid()) {
       *aResult = checkedResult.value();
       return true;
     } else {
       return false;
     }
   }
   @endcode
 *
 * Implicit conversion from plain integers to checked integers is allowed. The
 * plain integer is checked to be in range before being casted to the
 * destination type. This means that the following lines all compile, and the
 * resulting CheckedInts are correctly detected as valid or invalid:
 * @code
   // 1 is of type int, is found to be in range for uint8_t, x is valid
   CheckedInt<uint8_t> x(1);
   // -1 is of type int, is found not to be in range for uint8_t, x is invalid
   CheckedInt<uint8_t> x(-1);
   // -1 is of type int, is found to be in range for int8_t, x is valid
   CheckedInt<int8_t> x(-1);
   // 1000 is of type int16_t, is found not to be in range for int8_t,
   // x is invalid
   CheckedInt<int8_t> x(int16_t(1000));
   // 3123456789 is of type uint32_t, is found not to be in range for int32_t,
   // x is invalid
   CheckedInt<int32_t> x(uint32_t(3123456789));
 * @endcode
 * Implicit conversion from
 * checked integers to plain integers is not allowed. As shown in the
 * above example, to get the value of a checked integer as a normal integer,
 * call value().
 *
 * Arithmetic operations between checked and plain integers is allowed; the
 * result type is the type of the checked integer.
 *
 * Checked integers of different types cannot be used in the same arithmetic
 * expression.
 *
 * There are convenience typedefs for all stdint types, of the following form
 * (these are just 2 examples):
   @code
   typedef CheckedInt<int32_t> CheckedInt32;
   typedef CheckedInt<uint16_t> CheckedUint16;
   @endcode
 */
template<typename T>
class CheckedInt
{
protected:
  T mValue;
  bool mIsValid;

  template<typename U>
  CheckedInt(U aValue, bool aIsValid) : mValue(aValue), mIsValid(aIsValid)
  {
    static_assert(detail::IsSupported<T>::value &&
                  detail::IsSupported<U>::value,
                  "This type is not supported by CheckedInt");
  }

  friend struct detail::NegateImpl<T>;

public:
  /**
   * Constructs a checked integer with given @a value. The checked integer is
   * initialized as valid or invalid depending on whether the @a value
   * is in range.
   *
   * This constructor is not explicit. Instead, the type of its argument is a
   * separate template parameter, ensuring that no conversion is performed
   * before this constructor is actually called. As explained in the above
   * documentation for class CheckedInt, this constructor checks that its
   * argument is valid.
   */
  template<typename U>
  MOZ_IMPLICIT CheckedInt(U aValue) MOZ_NO_ARITHMETIC_EXPR_IN_ARGUMENT
    : mValue(T(aValue)),
      mIsValid(detail::IsInRange<T>(aValue))
  {
    static_assert(detail::IsSupported<T>::value &&
                  detail::IsSupported<U>::value,
                  "This type is not supported by CheckedInt");
  }

  template<typename U>
  friend class CheckedInt;

  template<typename U>
  CheckedInt<U> toChecked() const
  {
    CheckedInt<U> ret(mValue);
    ret.mIsValid = ret.mIsValid && mIsValid;
    return ret;
  }

  /** Constructs a valid checked integer with initial value 0 */
  CheckedInt() : mValue(0), mIsValid(true)
  {
    static_assert(detail::IsSupported<T>::value,
                  "This type is not supported by CheckedInt");
  }

  /** @returns the actual value */
  T value() const
  {
    MOZ_ASSERT(mIsValid, "Invalid checked integer (division by zero or integer overflow)");
    return mValue;
  }

  /**
   * @returns true if the checked integer is valid, i.e. is not the result
   * of an invalid operation or of an operation involving an invalid checked
   * integer
   */
  bool isValid() const
  {
    return mIsValid;
  }

  template<typename U>
  friend CheckedInt<U> operator +(const CheckedInt<U>& aLhs,
                                  const CheckedInt<U>& aRhs);
  template<typename U>
  CheckedInt& operator +=(U aRhs);
  CheckedInt& operator +=(const CheckedInt<T>& aRhs);

  template<typename U>
  friend CheckedInt<U> operator -(const CheckedInt<U>& aLhs,
                                  const CheckedInt<U>& aRhs);
  template<typename U>
  CheckedInt& operator -=(U aRhs);
  CheckedInt& operator -=(const CheckedInt<T>& aRhs);

  template<typename U>
  friend CheckedInt<U> operator *(const CheckedInt<U>& aLhs,
                                  const CheckedInt<U>& aRhs);
  template<typename U>
  CheckedInt& operator *=(U aRhs);
  CheckedInt& operator *=(const CheckedInt<T>& aRhs);

  template<typename U>
  friend CheckedInt<U> operator /(const CheckedInt<U>& aLhs,
                                  const CheckedInt<U>& aRhs);
  template<typename U>
  CheckedInt& operator /=(U aRhs);
  CheckedInt& operator /=(const CheckedInt<T>& aRhs);

  template<typename U>
  friend CheckedInt<U> operator %(const CheckedInt<U>& aLhs,
                                  const CheckedInt<U>& aRhs);
  template<typename U>
  CheckedInt& operator %=(U aRhs);
  CheckedInt& operator %=(const CheckedInt<T>& aRhs);

  CheckedInt operator -() const
  {
    return detail::NegateImpl<T>::negate(*this);
  }

  /**
   * @returns true if the left and right hand sides are valid
   * and have the same value.
   *
   * Note that these semantics are the reason why we don't offer
   * a operator!=. Indeed, we'd want to have a!=b be equivalent to !(a==b)
   * but that would mean that whenever a or b is invalid, a!=b
   * is always true, which would be very confusing.
   *
   * For similar reasons, operators <, >, <=, >= would be very tricky to
   * specify, so we just avoid offering them.
   *
   * Notice that these == semantics are made more reasonable by these facts:
   *  1. a==b implies equality at the raw data level
   *     (the converse is false, as a==b is never true among invalids)
   *  2. This is similar to the behavior of IEEE floats, where a==b
   *     means that a and b have the same value *and* neither is NaN.
   */
  bool operator ==(const CheckedInt& aOther) const
  {
    return mIsValid && aOther.mIsValid && mValue == aOther.mValue;
  }

  /** prefix ++ */
  CheckedInt& operator++()
  {
    *this += 1;
    return *this;
  }

  /** postfix ++ */
  CheckedInt operator++(int)
  {
    CheckedInt tmp = *this;
    *this += 1;
    return tmp;
  }

  /** prefix -- */
  CheckedInt& operator--()
  {
    *this -= 1;
    return *this;
  }

  /** postfix -- */
  CheckedInt operator--(int)
  {
    CheckedInt tmp = *this;
    *this -= 1;
    return tmp;
  }

private:
  /**
   * The !=, <, <=, >, >= operators are disabled:
   * see the comment on operator==.
   */
  template<typename U> bool operator !=(U aOther) const = delete;
  template<typename U> bool operator < (U aOther) const = delete;
  template<typename U> bool operator <=(U aOther) const = delete;
  template<typename U> bool operator > (U aOther) const = delete;
  template<typename U> bool operator >=(U aOther) const = delete;
};

#define MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(NAME, OP)                        \
  template<typename T>                                                        \
  inline CheckedInt<T>                                                        \
  operator OP(const CheckedInt<T>& aLhs, const CheckedInt<T>& aRhs)           \
  {                                                                           \
    if (!detail::Is##NAME##Valid(aLhs.mValue, aRhs.mValue)) {                 \
      return CheckedInt<T>(0, false);                                         \
    }                                                                         \
    return CheckedInt<T>(aLhs.mValue OP aRhs.mValue,                          \
                         aLhs.mIsValid && aRhs.mIsValid);                     \
  }

MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(Add, +)
MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(Sub, -)
MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(Mul, *)
MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(Div, /)
MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(Mod, %)

#undef MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR

// Implement castToCheckedInt<T>(x), making sure that
//  - it allows x to be either a CheckedInt<T> or any integer type
//    that can be casted to T
//  - if x is already a CheckedInt<T>, we just return a reference to it,
//    instead of copying it (optimization)

namespace detail {

template<typename T, typename U>
struct CastToCheckedIntImpl
{
  typedef CheckedInt<T> ReturnType;
  static CheckedInt<T> run(U aU) { return aU; }
};

template<typename T>
struct CastToCheckedIntImpl<T, CheckedInt<T> >
{
  typedef const CheckedInt<T>& ReturnType;
  static const CheckedInt<T>& run(const CheckedInt<T>& aU) { return aU; }
};

} // namespace detail

template<typename T, typename U>
inline typename detail::CastToCheckedIntImpl<T, U>::ReturnType
castToCheckedInt(U aU)
{
  static_assert(detail::IsSupported<T>::value &&
                detail::IsSupported<U>::value,
                "This type is not supported by CheckedInt");
  return detail::CastToCheckedIntImpl<T, U>::run(aU);
}

#define MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(OP, COMPOUND_OP)            \
  template<typename T>                                                          \
  template<typename U>                                                          \
  CheckedInt<T>& CheckedInt<T>::operator COMPOUND_OP(U aRhs)                    \
  {                                                                             \
    *this = *this OP castToCheckedInt<T>(aRhs);                                 \
    return *this;                                                               \
  }                                                                             \
  template<typename T>                                                          \
  CheckedInt<T>& CheckedInt<T>::operator COMPOUND_OP(const CheckedInt<T>& aRhs) \
  {                                                                             \
    *this = *this OP aRhs;                                                      \
    return *this;                                                               \
  }                                                                             \
  template<typename T, typename U>                                              \
  inline CheckedInt<T> operator OP(const CheckedInt<T>& aLhs, U aRhs)           \
  {                                                                             \
    return aLhs OP castToCheckedInt<T>(aRhs);                                   \
  }                                                                             \
  template<typename T, typename U>                                              \
  inline CheckedInt<T> operator OP(U aLhs, const CheckedInt<T>& aRhs)           \
  {                                                                             \
    return castToCheckedInt<T>(aLhs) OP aRhs;                                   \
  }

MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(+, +=)
MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(*, *=)
MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(-, -=)
MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(/, /=)
MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(%, %=)

#undef MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS

template<typename T, typename U>
inline bool
operator ==(const CheckedInt<T>& aLhs, U aRhs)
{
  return aLhs == castToCheckedInt<T>(aRhs);
}

template<typename T, typename U>
inline bool
operator ==(U aLhs, const CheckedInt<T>& aRhs)
{
  return castToCheckedInt<T>(aLhs) == aRhs;
}

// Convenience typedefs.
typedef CheckedInt<int8_t>   CheckedInt8;
typedef CheckedInt<uint8_t>  CheckedUint8;
typedef CheckedInt<int16_t>  CheckedInt16;
typedef CheckedInt<uint16_t> CheckedUint16;
typedef CheckedInt<int32_t>  CheckedInt32;
typedef CheckedInt<uint32_t> CheckedUint32;
typedef CheckedInt<int64_t>  CheckedInt64;
typedef CheckedInt<uint64_t> CheckedUint64;

} // namespace mozilla

#endif /* mozilla_CheckedInt_h */