comparison osx/include/kj/units.h @ 62:0994c39f1e94

Cap'n Proto v0.6 + build for OSX

 #if defined(__GNUC__) && !KJ_HEADER_WARNINGS
 #pragma GCC system_header
 #endif
 
 #include "common.h"
+#include <inttypes.h>
 
 namespace kj {
 
 // =======================================================================================
 // IDs

   inline constexpr bool operator> (const Id& other) const { return value >  other.value; }
 };
 
 // =======================================================================================
 // Quantity and UnitRatio -- implement unit analysis via the type system
+
+struct Unsafe_ {};
+constexpr Unsafe_ unsafe = Unsafe_();
+// Use as a parameter to constructors that are unsafe to indicate that you really do mean it.
+
+template <uint64_t maxN, typename T>
+class Bounded;
+template <uint value>
+class BoundedConst;
 
 template <typename T> constexpr bool isIntegral() { return false; }
 template <> constexpr bool isIntegral<char>() { return true; }
 template <> constexpr bool isIntegral<signed char>() { return true; }
 template <> constexpr bool isIntegral<short>() { return true; }

 template <> constexpr bool isIntegral<unsigned short>() { return true; }
 template <> constexpr bool isIntegral<unsigned int>() { return true; }
 template <> constexpr bool isIntegral<unsigned long>() { return true; }
 template <> constexpr bool isIntegral<unsigned long long>() { return true; }
 
+template <typename T>
+struct IsIntegralOrBounded_ { static constexpr bool value = isIntegral<T>(); };
+template <uint64_t m, typename T>
+struct IsIntegralOrBounded_<Bounded<m, T>> { static constexpr bool value = true; };
+template <uint v>
+struct IsIntegralOrBounded_<BoundedConst<v>> { static constexpr bool value = true; };
+
+template <typename T>
+inline constexpr bool isIntegralOrBounded() { return IsIntegralOrBounded_<T>::value; }
+
 template <typename Number, typename Unit1, typename Unit2>
 class UnitRatio {
   // A multiplier used to convert Quantities of one unit to Quantities of another unit.  See
   // Quantity, below.
   //
   // Construct this type by dividing one Quantity by another of a different unit.  Use this type
   // by multiplying it by a Quantity, or dividing a Quantity by it.
 
-  static_assert(isIntegral<Number>(), "Underlying type for UnitRatio must be integer.");
+  static_assert(isIntegralOrBounded<Number>(),
+      "Underlying type for UnitRatio must be integer.");
 
 public:
   inline UnitRatio() {}
 
-  constexpr explicit UnitRatio(Number unit1PerUnit2): unit1PerUnit2(unit1PerUnit2) {}
+  constexpr UnitRatio(Number unit1PerUnit2, decltype(unsafe)): unit1PerUnit2(unit1PerUnit2) {}
   // This constructor was intended to be private, but GCC complains about it being private in a
   // bunch of places that don't appear to even call it, so I made it public.  Oh well.
 
   template <typename OtherNumber>
   inline constexpr UnitRatio(const UnitRatio<OtherNumber, Unit1, Unit2>& other)
       : unit1PerUnit2(other.unit1PerUnit2) {}
 
   template <typename OtherNumber>
-  inline constexpr UnitRatio<decltype(Number(1)+OtherNumber(1)), Unit1, Unit2>
+  inline constexpr UnitRatio<decltype(Number()+OtherNumber()), Unit1, Unit2>
       operator+(UnitRatio<OtherNumber, Unit1, Unit2> other) const {
-    return UnitRatio<decltype(Number(1)+OtherNumber(1)), Unit1, Unit2>(
-        unit1PerUnit2 + other.unit1PerUnit2);
-  }
-  template <typename OtherNumber>
-  inline constexpr UnitRatio<decltype(Number(1)-OtherNumber(1)), Unit1, Unit2>
+    return UnitRatio<decltype(Number()+OtherNumber()), Unit1, Unit2>(
+        unit1PerUnit2 + other.unit1PerUnit2, unsafe);
+  }
+  template <typename OtherNumber>
+  inline constexpr UnitRatio<decltype(Number()-OtherNumber()), Unit1, Unit2>
       operator-(UnitRatio<OtherNumber, Unit1, Unit2> other) const {
-    return UnitRatio<decltype(Number(1)-OtherNumber(1)), Unit1, Unit2>(
-        unit1PerUnit2 - other.unit1PerUnit2);
+    return UnitRatio<decltype(Number()-OtherNumber()), Unit1, Unit2>(
+        unit1PerUnit2 - other.unit1PerUnit2, unsafe);
   }
 
   template <typename OtherNumber, typename Unit3>
-  inline constexpr UnitRatio<decltype(Number(1)*OtherNumber(1)), Unit3, Unit2>
+  inline constexpr UnitRatio<decltype(Number()*OtherNumber()), Unit3, Unit2>
       operator*(UnitRatio<OtherNumber, Unit3, Unit1> other) const {
     // U1 / U2 * U3 / U1 = U3 / U2
-    return UnitRatio<decltype(Number(1)*OtherNumber(1)), Unit3, Unit2>(
-        unit1PerUnit2 * other.unit1PerUnit2);
+    return UnitRatio<decltype(Number()*OtherNumber()), Unit3, Unit2>(
+        unit1PerUnit2 * other.unit1PerUnit2, unsafe);
   }
   template <typename OtherNumber, typename Unit3>
-  inline constexpr UnitRatio<decltype(Number(1)*OtherNumber(1)), Unit1, Unit3>
+  inline constexpr UnitRatio<decltype(Number()*OtherNumber()), Unit1, Unit3>
       operator*(UnitRatio<OtherNumber, Unit2, Unit3> other) const {
     // U1 / U2 * U2 / U3 = U1 / U3
-    return UnitRatio<decltype(Number(1)*OtherNumber(1)), Unit1, Unit3>(
-        unit1PerUnit2 * other.unit1PerUnit2);
+    return UnitRatio<decltype(Number()*OtherNumber()), Unit1, Unit3>(
+        unit1PerUnit2 * other.unit1PerUnit2, unsafe);
   }
 
   template <typename OtherNumber, typename Unit3>
-  inline constexpr UnitRatio<decltype(Number(1)*OtherNumber(1)), Unit3, Unit2>
+  inline constexpr UnitRatio<decltype(Number()*OtherNumber()), Unit3, Unit2>
       operator/(UnitRatio<OtherNumber, Unit1, Unit3> other) const {
     // (U1 / U2) / (U1 / U3) = U3 / U2
-    return UnitRatio<decltype(Number(1)*OtherNumber(1)), Unit3, Unit2>(
-        unit1PerUnit2 / other.unit1PerUnit2);
+    return UnitRatio<decltype(Number()*OtherNumber()), Unit3, Unit2>(
+        unit1PerUnit2 / other.unit1PerUnit2, unsafe);
   }
   template <typename OtherNumber, typename Unit3>
-  inline constexpr UnitRatio<decltype(Number(1)*OtherNumber(1)), Unit1, Unit3>
+  inline constexpr UnitRatio<decltype(Number()*OtherNumber()), Unit1, Unit3>
       operator/(UnitRatio<OtherNumber, Unit3, Unit2> other) const {
     // (U1 / U2) / (U3 / U2) = U1 / U3
-    return UnitRatio<decltype(Number(1)*OtherNumber(1)), Unit1, Unit3>(
-        unit1PerUnit2 / other.unit1PerUnit2);
-  }
-
-  template <typename OtherNumber>
-  inline decltype(Number(1) / OtherNumber(1))
+    return UnitRatio<decltype(Number()*OtherNumber()), Unit1, Unit3>(
+        unit1PerUnit2 / other.unit1PerUnit2, unsafe);
+  }
+
+  template <typename OtherNumber>
+  inline decltype(Number() / OtherNumber())
       operator/(UnitRatio<OtherNumber, Unit1, Unit2> other) const {
     return unit1PerUnit2 / other.unit1PerUnit2;
   }
 
   inline bool operator==(UnitRatio other) const { return unit1PerUnit2 == other.unit1PerUnit2; }

   template <typename OtherNumber, typename OtherUnit>
   friend class Quantity;
   template <typename OtherNumber, typename OtherUnit1, typename OtherUnit2>
   friend class UnitRatio;
 
-  template <typename N1, typename N2, typename U1, typename U2>
-  friend inline constexpr UnitRatio<decltype(N1(1) * N2(1)), U1, U2>
+  template <typename N1, typename N2, typename U1, typename U2, typename>
+  friend inline constexpr UnitRatio<decltype(N1() * N2()), U1, U2>
       operator*(N1, UnitRatio<N2, U1, U2>);
 };
 
-template <typename N1, typename N2, typename U1, typename U2>
-inline constexpr UnitRatio<decltype(N1(1) * N2(1)), U1, U2>
+template <typename N1, typename N2, typename U1, typename U2,
+          typename = EnableIf<isIntegralOrBounded<N1>() && isIntegralOrBounded<N2>()>>
+inline constexpr UnitRatio<decltype(N1() * N2()), U1, U2>
     operator*(N1 n, UnitRatio<N2, U1, U2> r) {
-  return UnitRatio<decltype(N1(1) * N2(1)), U1, U2>(n * r.unit1PerUnit2);
+  return UnitRatio<decltype(N1() * N2()), U1, U2>(n * r.unit1PerUnit2, unsafe);
 }
 
 template <typename Number, typename Unit>
 class Quantity {
   // A type-safe numeric quantity, specified in terms of some unit.  Two Quantities cannot be used

   //
   //   void waitThreeMinutes() {
   //     waitFor(3 * MINUTES);
   //   }
 
-  static_assert(isIntegral<Number>(), "Underlying type for Quantity must be integer.");
+  static_assert(isIntegralOrBounded<Number>(),
+      "Underlying type for Quantity must be integer.");
 
 public:
-  inline constexpr Quantity() {}
+  inline constexpr Quantity() = default;
 
   inline constexpr Quantity(MaxValue_): value(maxValue) {}
   inline constexpr Quantity(MinValue_): value(minValue) {}
   // Allow initialization from maxValue and minValue.
   // TODO(msvc): decltype(maxValue) and decltype(minValue) deduce unknown-type for these function
   // parameters, causing the compiler to complain of a duplicate constructor definition, so we
   // specify MaxValue_ and MinValue_ types explicitly.
 
-  inline explicit constexpr Quantity(Number value): value(value) {}
+  inline constexpr Quantity(Number value, decltype(unsafe)): value(value) {}
   // This constructor was intended to be private, but GCC complains about it being private in a
   // bunch of places that don't appear to even call it, so I made it public.  Oh well.
 
   template <typename OtherNumber>
   inline constexpr Quantity(const Quantity<OtherNumber, Unit>& other)
       : value(other.value) {}
 
   template <typename OtherNumber>
-  inline constexpr Quantity<decltype(Number(1) + OtherNumber(1)), Unit>
+  inline Quantity& operator=(const Quantity<OtherNumber, Unit>& other) {
+    value = other.value;
+    return *this;
+  }
+
+  template <typename OtherNumber>
+  inline constexpr Quantity<decltype(Number() + OtherNumber()), Unit>
       operator+(const Quantity<OtherNumber, Unit>& other) const {
-    return Quantity<decltype(Number(1) + OtherNumber(1)), Unit>(value + other.value);
-  }
-  template <typename OtherNumber>
-  inline constexpr Quantity<decltype(Number(1) - OtherNumber(1)), Unit>
+    return Quantity<decltype(Number() + OtherNumber()), Unit>(value + other.value, unsafe);
+  }
+  template <typename OtherNumber>
+  inline constexpr Quantity<decltype(Number() - OtherNumber()), Unit>
       operator-(const Quantity<OtherNumber, Unit>& other) const {
-    return Quantity<decltype(Number(1) - OtherNumber(1)), Unit>(value - other.value);
-  }
-  template <typename OtherNumber>
-  inline constexpr Quantity<decltype(Number(1) * OtherNumber(1)), Unit>
+    return Quantity<decltype(Number() - OtherNumber()), Unit>(value - other.value, unsafe);
+  }
+  template <typename OtherNumber, typename = EnableIf<isIntegralOrBounded<OtherNumber>()>>
+  inline constexpr Quantity<decltype(Number() * OtherNumber()), Unit>
       operator*(OtherNumber other) const {
-    static_assert(isIntegral<OtherNumber>(), "Multiplied Quantity by non-integer.");
-    return Quantity<decltype(Number(1) * other), Unit>(value * other);
-  }
-  template <typename OtherNumber>
-  inline constexpr Quantity<decltype(Number(1) / OtherNumber(1)), Unit>
+    return Quantity<decltype(Number() * other), Unit>(value * other, unsafe);
+  }
+  template <typename OtherNumber, typename = EnableIf<isIntegralOrBounded<OtherNumber>()>>
+  inline constexpr Quantity<decltype(Number() / OtherNumber()), Unit>
       operator/(OtherNumber other) const {
-    static_assert(isIntegral<OtherNumber>(), "Divided Quantity by non-integer.");
-    return Quantity<decltype(Number(1) / other), Unit>(value / other);
-  }
-  template <typename OtherNumber>
-  inline constexpr decltype(Number(1) / OtherNumber(1))
+    return Quantity<decltype(Number() / other), Unit>(value / other, unsafe);
+  }
+  template <typename OtherNumber>
+  inline constexpr decltype(Number() / OtherNumber())
       operator/(const Quantity<OtherNumber, Unit>& other) const {
     return value / other.value;
   }
   template <typename OtherNumber>
-  inline constexpr decltype(Number(1) % OtherNumber(1))
+  inline constexpr Quantity<decltype(Number() % OtherNumber()), Unit>
       operator%(const Quantity<OtherNumber, Unit>& other) const {
-    return value % other.value;
+    return Quantity<decltype(Number() % OtherNumber()), Unit>(value % other.value, unsafe);
   }
 
   template <typename OtherNumber, typename OtherUnit>
-  inline constexpr Quantity<decltype(Number(1) * OtherNumber(1)), OtherUnit>
-      operator*(const UnitRatio<OtherNumber, OtherUnit, Unit>& ratio) const {
-    return Quantity<decltype(Number(1) * OtherNumber(1)), OtherUnit>(
-        value * ratio.unit1PerUnit2);
+  inline constexpr Quantity<decltype(Number() * OtherNumber()), OtherUnit>
+      operator*(UnitRatio<OtherNumber, OtherUnit, Unit> ratio) const {
+    return Quantity<decltype(Number() * OtherNumber()), OtherUnit>(
+        value * ratio.unit1PerUnit2, unsafe);
   }
   template <typename OtherNumber, typename OtherUnit>
-  inline constexpr Quantity<decltype(Number(1) / OtherNumber(1)), OtherUnit>
-      operator/(const UnitRatio<OtherNumber, Unit, OtherUnit>& ratio) const {
-    return Quantity<decltype(Number(1) / OtherNumber(1)), OtherUnit>(
-        value / ratio.unit1PerUnit2);
+  inline constexpr Quantity<decltype(Number() / OtherNumber()), OtherUnit>
+      operator/(UnitRatio<OtherNumber, Unit, OtherUnit> ratio) const {
+    return Quantity<decltype(Number() / OtherNumber()), OtherUnit>(
+        value / ratio.unit1PerUnit2, unsafe);
   }
   template <typename OtherNumber, typename OtherUnit>
-  inline constexpr Quantity<decltype(Number(1) % OtherNumber(1)), Unit>
-      operator%(const UnitRatio<OtherNumber, Unit, OtherUnit>& ratio) const {
-    return Quantity<decltype(Number(1) % OtherNumber(1)), Unit>(
-        value % ratio.unit1PerUnit2);
+  inline constexpr Quantity<decltype(Number() % OtherNumber()), Unit>
+      operator%(UnitRatio<OtherNumber, Unit, OtherUnit> ratio) const {
+    return Quantity<decltype(Number() % OtherNumber()), Unit>(
+        value % ratio.unit1PerUnit2, unsafe);
   }
   template <typename OtherNumber, typename OtherUnit>
-  inline constexpr UnitRatio<decltype(Number(1) / OtherNumber(1)), Unit, OtherUnit>
-      operator/(const Quantity<OtherNumber, OtherUnit>& other) const {
-    return UnitRatio<decltype(Number(1) / OtherNumber(1)), Unit, OtherUnit>(value / other.value);
+  inline constexpr UnitRatio<decltype(Number() / OtherNumber()), Unit, OtherUnit>
+      operator/(Quantity<OtherNumber, OtherUnit> other) const {
+    return UnitRatio<decltype(Number() / OtherNumber()), Unit, OtherUnit>(
+        value / other.value, unsafe);
   }
 
   template <typename OtherNumber>
   inline constexpr bool operator==(const Quantity<OtherNumber, Unit>& other) const {
     return value == other.value;

   template <typename OtherNumber, typename OtherUnit>
   friend class Quantity;
 
   template <typename Number1, typename Number2, typename Unit2>
   friend inline constexpr auto operator*(Number1 a, Quantity<Number2, Unit2> b)
-      -> Quantity<decltype(Number1(1) * Number2(1)), Unit2>;
-
-  template <typename T>
-  friend inline constexpr T unit();
+      -> Quantity<decltype(Number1() * Number2()), Unit2>;
+};
+
+template <typename T> struct Unit_ {
+  static inline constexpr T get() { return T(1); }
+};
+template <typename T, typename U>
+struct Unit_<Quantity<T, U>> {
+  static inline constexpr Quantity<decltype(Unit_<T>::get()), U> get() {
+    return Quantity<decltype(Unit_<T>::get()), U>(Unit_<T>::get(), unsafe);
+  }
 };
 
 template <typename T>
-inline constexpr T unit() { return T(1); }
+inline constexpr auto unit() -> decltype(Unit_<T>::get()) { return Unit_<T>::get(); }
 // unit<Quantity<T, U>>() returns a Quantity of value 1.  It also, intentionally, works on basic
 // numeric types.
 
 template <typename Number1, typename Number2, typename Unit>
 inline constexpr auto operator*(Number1 a, Quantity<Number2, Unit> b)
-    -> Quantity<decltype(Number1(1) * Number2(1)), Unit> {
-  return Quantity<decltype(Number1(1) * Number2(1)), Unit>(a * b.value);
+    -> Quantity<decltype(Number1() * Number2()), Unit> {
+  return Quantity<decltype(Number1() * Number2()), Unit>(a * b.value, unsafe);
 }
 
 template <typename Number1, typename Number2, typename Unit, typename Unit2>
 inline constexpr auto operator*(UnitRatio<Number1, Unit2, Unit> ratio,
     Quantity<Number2, Unit> measure)

 template <typename T>
 inline constexpr T origin() { return T(0 * unit<UnitOf<T>>()); }
 // origin<Absolute<T, U>>() returns an Absolute of value 0.  It also, intentionally, works on basic
 // numeric types.
 
+// =======================================================================================
+// Overflow avoidance
+
+template <uint64_t n, uint accum = 0>
+struct BitCount_ {
+  static constexpr uint value = BitCount_<(n >> 1), accum + 1>::value;
+};
+template <uint accum>
+struct BitCount_<0, accum> {
+  static constexpr uint value = accum;
+};
+
+template <uint64_t n>
+inline constexpr uint bitCount() { return BitCount_<n>::value; }
+// Number of bits required to represent the number `n`.
+
+template <uint bitCountBitCount> struct AtLeastUInt_ {
+  static_assert(bitCountBitCount < 7, "don't know how to represent integers over 64 bits");
+};
+template <> struct AtLeastUInt_<0> { typedef uint8_t Type; };
+template <> struct AtLeastUInt_<1> { typedef uint8_t Type; };
+template <> struct AtLeastUInt_<2> { typedef uint8_t Type; };
+template <> struct AtLeastUInt_<3> { typedef uint8_t Type; };
+template <> struct AtLeastUInt_<4> { typedef uint16_t Type; };
+template <> struct AtLeastUInt_<5> { typedef uint32_t Type; };
+template <> struct AtLeastUInt_<6> { typedef uint64_t Type; };
+
+template <uint bits>
+using AtLeastUInt = typename AtLeastUInt_<bitCount<max(bits, 1) - 1>()>::Type;
+// AtLeastUInt<n> is an unsigned integer of at least n bits. E.g. AtLeastUInt<12> is uint16_t.
+
+// -------------------------------------------------------------------
+
+template <uint value>
+class BoundedConst {
+  // A constant integer value on which we can do bit size analysis.
+
+public:
+  BoundedConst() = default;
+
+  inline constexpr uint unwrap() const { return value; }
+
+#define OP(op, check) \
+  template <uint other> \
+  inline constexpr BoundedConst<(value op other)> \
+      operator op(BoundedConst<other>) const { \
+    static_assert(check, "overflow in BoundedConst arithmetic"); \
+    return BoundedConst<(value op other)>(); \
+  }
+#define COMPARE_OP(op) \
+  template <uint other> \
+  inline constexpr bool operator op(BoundedConst<other>) const { \
+    return value op other; \
+  }
+
+  OP(+, value + other >= value)
+  OP(-, value - other <= value)
+  OP(*, value * other / other == value)
+  OP(/, true)   // div by zero already errors out; no other division ever overflows
+  OP(%, true)   // mod by zero already errors out; no other modulus ever overflows
+  OP(<<, value << other >= value)
+  OP(>>, true)  // right shift can't overflow
+  OP(&, true)   // bitwise ops can't overflow
+  OP(|, true)   // bitwise ops can't overflow
+
+  COMPARE_OP(==)
+  COMPARE_OP(!=)
+  COMPARE_OP(< )
+  COMPARE_OP(> )
+  COMPARE_OP(<=)
+  COMPARE_OP(>=)
+#undef OP
+#undef COMPARE_OP
+};
+
+template <uint64_t m, typename T>
+struct Unit_<Bounded<m, T>> {
+  static inline constexpr BoundedConst<1> get() { return BoundedConst<1>(); }
+};
+
+template <uint value>
+struct Unit_<BoundedConst<value>> {
+  static inline constexpr BoundedConst<1> get() { return BoundedConst<1>(); }
+};
+
+template <uint value>
+inline constexpr BoundedConst<value> bounded() {
+  return BoundedConst<value>();
+}
+
+template <uint64_t a, uint64_t b>
+static constexpr uint64_t boundedAdd() {
+  static_assert(a + b >= a, "possible overflow detected");
+  return a + b;
+}
+template <uint64_t a, uint64_t b>
+static constexpr uint64_t boundedSub() {
+  static_assert(a - b <= a, "possible underflow detected");
+  return a - b;
+}
+template <uint64_t a, uint64_t b>
+static constexpr uint64_t boundedMul() {
+  static_assert(a * b / b == a, "possible overflow detected");
+  return a * b;
+}
+template <uint64_t a, uint64_t b>
+static constexpr uint64_t boundedLShift() {
+  static_assert(a << b >= a, "possible overflow detected");
+  return a << b;
+}
+
+template <uint a, uint b>
+inline constexpr BoundedConst<kj::min(a, b)> min(BoundedConst<a>, BoundedConst<b>) {
+  return bounded<kj::min(a, b)>();
+}
+template <uint a, uint b>
+inline constexpr BoundedConst<kj::max(a, b)> max(BoundedConst<a>, BoundedConst<b>) {
+  return bounded<kj::max(a, b)>();
+}
+// We need to override min() and max() between constants because the ternary operator in the
+// default implementation would complain.
+
+// -------------------------------------------------------------------
+
+template <uint64_t maxN, typename T>
+class Bounded {
+public:
+  static_assert(maxN <= T(kj::maxValue), "possible overflow detected");
+
+  Bounded() = default;
+
+  Bounded(const Bounded& other) = default;
+  template <typename OtherInt, typename = EnableIf<isIntegral<OtherInt>()>>
+  inline constexpr Bounded(OtherInt value): value(value) {
+    static_assert(OtherInt(maxValue) <= maxN, "possible overflow detected");
+  }
+  template <uint64_t otherMax, typename OtherT>
+  inline constexpr Bounded(const Bounded<otherMax, OtherT>& other)
+      : value(other.value) {
+    static_assert(otherMax <= maxN, "possible overflow detected");
+  }
+  template <uint otherValue>
+  inline constexpr Bounded(BoundedConst<otherValue>)
+      : value(otherValue) {
+    static_assert(otherValue <= maxN, "overflow detected");
+  }
+
+  Bounded& operator=(const Bounded& other) = default;
+  template <typename OtherInt, typename = EnableIf<isIntegral<OtherInt>()>>
+  Bounded& operator=(OtherInt other) {
+    static_assert(OtherInt(maxValue) <= maxN, "possible overflow detected");
+    value = other;
+    return *this;
+  }
+  template <uint64_t otherMax, typename OtherT>
+  inline Bounded& operator=(const Bounded<otherMax, OtherT>& other) {
+    static_assert(otherMax <= maxN, "possible overflow detected");
+    value = other.value;
+    return *this;
+  }
+  template <uint otherValue>
+  inline Bounded& operator=(BoundedConst<otherValue>) {
+    static_assert(otherValue <= maxN, "overflow detected");
+    value = otherValue;
+    return *this;
+  }
+
+  inline constexpr T unwrap() const { return value; }
+
+#define OP(op, newMax) \
+  template <uint64_t otherMax, typename otherT> \
+  inline constexpr Bounded<newMax, decltype(T() op otherT())> \
+      operator op(const Bounded<otherMax, otherT>& other) const { \
+    return Bounded<newMax, decltype(T() op otherT())>(value op other.value, unsafe); \
+  }
+#define COMPARE_OP(op) \
+  template <uint64_t otherMax, typename OtherT> \
+  inline constexpr bool operator op(const Bounded<otherMax, OtherT>& other) const { \
+    return value op other.value; \
+  }
+
+  OP(+, (boundedAdd<maxN, otherMax>()))
+  OP(*, (boundedMul<maxN, otherMax>()))
+  OP(/, maxN)
+  OP(%, otherMax - 1)
+
+  // operator- is intentionally omitted because we mostly use this with unsigned types, and
+  // subtraction requires proof that subtrahend is not greater than the minuend.
+
+  COMPARE_OP(==)
+  COMPARE_OP(!=)
+  COMPARE_OP(< )
+  COMPARE_OP(> )
+  COMPARE_OP(<=)
+  COMPARE_OP(>=)
+
+#undef OP
+#undef COMPARE_OP
+
+  template <uint64_t newMax, typename ErrorFunc>
+  inline Bounded<newMax, T> assertMax(ErrorFunc&& func) const {
+    // Assert that the number is no more than `newMax`. Otherwise, call `func`.
+    static_assert(newMax < maxN, "this bounded size assertion is redundant");
+    if (KJ_UNLIKELY(value > newMax)) func();
+    return Bounded<newMax, T>(value, unsafe);
+  }
+
+  template <uint64_t otherMax, typename OtherT, typename ErrorFunc>
+  inline Bounded<maxN, decltype(T() - OtherT())> subtractChecked(
+      const Bounded<otherMax, OtherT>& other, ErrorFunc&& func) const {
+    // Subtract a number, calling func() if the result would underflow.
+    if (KJ_UNLIKELY(value < other.value)) func();
+    return Bounded<maxN, decltype(T() - OtherT())>(value - other.value, unsafe);
+  }
+
+  template <uint otherValue, typename ErrorFunc>
+  inline Bounded<maxN - otherValue, T> subtractChecked(
+      BoundedConst<otherValue>, ErrorFunc&& func) const {
+    // Subtract a number, calling func() if the result would underflow.
+    static_assert(otherValue <= maxN, "underflow detected");
+    if (KJ_UNLIKELY(value < otherValue)) func();
+    return Bounded<maxN - otherValue, T>(value - otherValue, unsafe);
+  }
+
+  template <uint64_t otherMax, typename OtherT>
+  inline Maybe<Bounded<maxN, decltype(T() - OtherT())>> trySubtract(
+      const Bounded<otherMax, OtherT>& other) const {
+    // Subtract a number, calling func() if the result would underflow.
+    if (value < other.value) {
+      return nullptr;
+    } else {
+      return Bounded<maxN, decltype(T() - OtherT())>(value - other.value, unsafe);
+    }
+  }
+
+  template <uint otherValue>
+  inline Maybe<Bounded<maxN - otherValue, T>> trySubtract(BoundedConst<otherValue>) const {
+    // Subtract a number, calling func() if the result would underflow.
+    if (value < otherValue) {
+      return nullptr;
+    } else {
+      return Bounded<maxN - otherValue, T>(value - otherValue, unsafe);
+    }
+  }
+
+  inline constexpr Bounded(T value, decltype(unsafe)): value(value) {}
+  template <uint64_t otherMax, typename OtherT>
+  inline constexpr Bounded(Bounded<otherMax, OtherT> value, decltype(unsafe))
+      : value(value.value) {}
+  // Mainly for internal use.
+  //
+  // Only use these as a last resort, with ample commentary on why you think it's safe.
+
+private:
+  T value;
+
+  template <uint64_t, typename>
+  friend class Bounded;
+};
+
+template <typename Number>
+inline constexpr Bounded<Number(kj::maxValue), Number> bounded(Number value) {
+  return Bounded<Number(kj::maxValue), Number>(value, unsafe);
+}
+
+inline constexpr Bounded<1, uint8_t> bounded(bool value) {
+  return Bounded<1, uint8_t>(value, unsafe);
+}
+
+template <uint bits, typename Number>
+inline constexpr Bounded<maxValueForBits<bits>(), Number> assumeBits(Number value) {
+  return Bounded<maxValueForBits<bits>(), Number>(value, unsafe);
+}
+
+template <uint bits, uint64_t maxN, typename T>
+inline constexpr Bounded<maxValueForBits<bits>(), T> assumeBits(Bounded<maxN, T> value) {
+  return Bounded<maxValueForBits<bits>(), T>(value, unsafe);
+}
+
+template <uint bits, typename Number, typename Unit>
+inline constexpr auto assumeBits(Quantity<Number, Unit> value)
+    -> Quantity<decltype(assumeBits<bits>(value / unit<Quantity<Number, Unit>>())), Unit> {
+  return Quantity<decltype(assumeBits<bits>(value / unit<Quantity<Number, Unit>>())), Unit>(
+      assumeBits<bits>(value / unit<Quantity<Number, Unit>>()), unsafe);
+}
+
+template <uint64_t maxN, typename Number>
+inline constexpr Bounded<maxN, Number> assumeMax(Number value) {
+  return Bounded<maxN, Number>(value, unsafe);
+}
+
+template <uint64_t newMaxN, uint64_t maxN, typename T>
+inline constexpr Bounded<newMaxN, T> assumeMax(Bounded<maxN, T> value) {
+  return Bounded<newMaxN, T>(value, unsafe);
+}
+
+template <uint64_t maxN, typename Number, typename Unit>
+inline constexpr auto assumeMax(Quantity<Number, Unit> value)
+    -> Quantity<decltype(assumeMax<maxN>(value / unit<Quantity<Number, Unit>>())), Unit> {
+  return Quantity<decltype(assumeMax<maxN>(value / unit<Quantity<Number, Unit>>())), Unit>(
+      assumeMax<maxN>(value / unit<Quantity<Number, Unit>>()), unsafe);
+}
+
+template <uint maxN, typename Number>
+inline constexpr Bounded<maxN, Number> assumeMax(BoundedConst<maxN>, Number value) {
+  return assumeMax<maxN>(value);
+}
+
+template <uint newMaxN, uint64_t maxN, typename T>
+inline constexpr Bounded<newMaxN, T> assumeMax(BoundedConst<maxN>, Bounded<maxN, T> value) {
+  return assumeMax<maxN>(value);
+}
+
+template <uint maxN, typename Number, typename Unit>
+inline constexpr auto assumeMax(Quantity<BoundedConst<maxN>, Unit>, Quantity<Number, Unit> value)
+    -> decltype(assumeMax<maxN>(value)) {
+  return assumeMax<maxN>(value);
+}
+
+template <uint64_t newMax, uint64_t maxN, typename T, typename ErrorFunc>
+inline Bounded<newMax, T> assertMax(Bounded<maxN, T> value, ErrorFunc&& errorFunc) {
+  // Assert that the bounded value is less than or equal to the given maximum, calling errorFunc()
+  // if not.
+  static_assert(newMax < maxN, "this bounded size assertion is redundant");
+  return value.template assertMax<newMax>(kj::fwd<ErrorFunc>(errorFunc));
+}
+
+template <uint64_t newMax, uint64_t maxN, typename T, typename Unit, typename ErrorFunc>
+inline Quantity<Bounded<newMax, T>, Unit> assertMax(
+    Quantity<Bounded<maxN, T>, Unit> value, ErrorFunc&& errorFunc) {
+  // Assert that the bounded value is less than or equal to the given maximum, calling errorFunc()
+  // if not.
+  static_assert(newMax < maxN, "this bounded size assertion is redundant");
+  return (value / unit<decltype(value)>()).template assertMax<newMax>(
+      kj::fwd<ErrorFunc>(errorFunc)) * unit<decltype(value)>();
+}
+
+template <uint newMax, uint64_t maxN, typename T, typename ErrorFunc>
+inline Bounded<newMax, T> assertMax(
+    BoundedConst<newMax>, Bounded<maxN, T> value, ErrorFunc&& errorFunc) {
+  return assertMax<newMax>(value, kj::mv(errorFunc));
+}
+
+template <uint newMax, uint64_t maxN, typename T, typename Unit, typename ErrorFunc>
+inline Quantity<Bounded<newMax, T>, Unit> assertMax(
+    Quantity<BoundedConst<newMax>, Unit>,
+    Quantity<Bounded<maxN, T>, Unit> value, ErrorFunc&& errorFunc) {
+  return assertMax<newMax>(value, kj::mv(errorFunc));
+}
+
+template <uint64_t newBits, uint64_t maxN, typename T, typename ErrorFunc = ThrowOverflow>
+inline Bounded<maxValueForBits<newBits>(), T> assertMaxBits(
+    Bounded<maxN, T> value, ErrorFunc&& errorFunc = ErrorFunc()) {
+  // Assert that the bounded value requires no more than the given number of bits, calling
+  // errorFunc() if not.
+  return assertMax<maxValueForBits<newBits>()>(value, kj::fwd<ErrorFunc>(errorFunc));
+}
+
+template <uint64_t newBits, uint64_t maxN, typename T, typename Unit,
+          typename ErrorFunc = ThrowOverflow>
+inline Quantity<Bounded<maxValueForBits<newBits>(), T>, Unit> assertMaxBits(
+    Quantity<Bounded<maxN, T>, Unit> value, ErrorFunc&& errorFunc = ErrorFunc()) {
+  // Assert that the bounded value requires no more than the given number of bits, calling
+  // errorFunc() if not.
+  return assertMax<maxValueForBits<newBits>()>(value, kj::fwd<ErrorFunc>(errorFunc));
+}
+
+template <typename newT, uint64_t maxN, typename T>
+inline constexpr Bounded<maxN, newT> upgradeBound(Bounded<maxN, T> value) {
+  return value;
+}
+
+template <typename newT, uint64_t maxN, typename T, typename Unit>
+inline constexpr Quantity<Bounded<maxN, newT>, Unit> upgradeBound(
+    Quantity<Bounded<maxN, T>, Unit> value) {
+  return value;
+}
+
+template <uint64_t maxN, typename T, typename Other, typename ErrorFunc>
+inline auto subtractChecked(Bounded<maxN, T> value, Other other, ErrorFunc&& errorFunc)
+    -> decltype(value.subtractChecked(other, kj::fwd<ErrorFunc>(errorFunc))) {
+  return value.subtractChecked(other, kj::fwd<ErrorFunc>(errorFunc));
+}
+
+template <typename T, typename U, typename Unit, typename ErrorFunc>
+inline auto subtractChecked(Quantity<T, Unit> value, Quantity<U, Unit> other, ErrorFunc&& errorFunc)
+    -> Quantity<decltype(subtractChecked(T(), U(), kj::fwd<ErrorFunc>(errorFunc))), Unit> {
+  return subtractChecked(value / unit<Quantity<T, Unit>>(),
+                         other / unit<Quantity<U, Unit>>(),
+                         kj::fwd<ErrorFunc>(errorFunc))
+      * unit<Quantity<T, Unit>>();
+}
+
+template <uint64_t maxN, typename T, typename Other>
+inline auto trySubtract(Bounded<maxN, T> value, Other other)
+    -> decltype(value.trySubtract(other)) {
+  return value.trySubtract(other);
+}
+
+template <typename T, typename U, typename Unit>
+inline auto trySubtract(Quantity<T, Unit> value, Quantity<U, Unit> other)
+    -> Maybe<Quantity<decltype(subtractChecked(T(), U(), int())), Unit>> {
+  return trySubtract(value / unit<Quantity<T, Unit>>(),
+                     other / unit<Quantity<U, Unit>>())
+      .map([](decltype(subtractChecked(T(), U(), int())) x) {
+    return x * unit<Quantity<T, Unit>>();
+  });
+}
+
+template <uint64_t aN, uint64_t bN, typename A, typename B>
+inline constexpr Bounded<kj::min(aN, bN), WiderType<A, B>>
+min(Bounded<aN, A> a, Bounded<bN, B> b) {
+  return Bounded<kj::min(aN, bN), WiderType<A, B>>(kj::min(a.unwrap(), b.unwrap()), unsafe);
+}
+template <uint64_t aN, uint64_t bN, typename A, typename B>
+inline constexpr Bounded<kj::max(aN, bN), WiderType<A, B>>
+max(Bounded<aN, A> a, Bounded<bN, B> b) {
+  return Bounded<kj::max(aN, bN), WiderType<A, B>>(kj::max(a.unwrap(), b.unwrap()), unsafe);
+}
+// We need to override min() and max() because:
+// 1) WiderType<> might not choose the correct bounds.
+// 2) One of the two sides of the ternary operator in the default implementation would fail to
+//    typecheck even though it is OK in practice.
+
+// -------------------------------------------------------------------
+// Operators between Bounded and BoundedConst
+
+#define OP(op, newMax) \
+template <uint64_t maxN, uint cvalue, typename T> \
+inline constexpr Bounded<(newMax), decltype(T() op uint())> operator op( \
+    Bounded<maxN, T> value, BoundedConst<cvalue>) { \
+  return Bounded<(newMax), decltype(T() op uint())>(value.unwrap() op cvalue, unsafe); \
+}
+
+#define REVERSE_OP(op, newMax) \
+template <uint64_t maxN, uint cvalue, typename T> \
+inline constexpr Bounded<(newMax), decltype(uint() op T())> operator op( \
+    BoundedConst<cvalue>, Bounded<maxN, T> value) { \
+  return Bounded<(newMax), decltype(uint() op T())>(cvalue op value.unwrap(), unsafe); \
+}
+
+#define COMPARE_OP(op) \
+template <uint64_t maxN, uint cvalue, typename T> \
+inline constexpr bool operator op(Bounded<maxN, T> value, BoundedConst<cvalue>) { \
+  return value.unwrap() op cvalue; \
+} \
+template <uint64_t maxN, uint cvalue, typename T> \
+inline constexpr bool operator op(BoundedConst<cvalue>, Bounded<maxN, T> value) { \
+  return cvalue op value.unwrap(); \
+}
+
+OP(+, (boundedAdd<maxN, cvalue>()))
+REVERSE_OP(+, (boundedAdd<maxN, cvalue>()))
+
+OP(*, (boundedMul<maxN, cvalue>()))
+REVERSE_OP(*, (boundedAdd<maxN, cvalue>()))
+
+OP(/, maxN / cvalue)
+REVERSE_OP(/, cvalue)  // denominator could be 1
+
+OP(%, cvalue - 1)
+REVERSE_OP(%, maxN - 1)
+
+OP(<<, (boundedLShift<maxN, cvalue>()))
+REVERSE_OP(<<, (boundedLShift<cvalue, maxN>()))
+
+OP(>>, maxN >> cvalue)
+REVERSE_OP(>>, cvalue >> maxN)
+
+OP(&, maxValueForBits<bitCount<maxN>()>() & cvalue)
+REVERSE_OP(&, maxValueForBits<bitCount<maxN>()>() & cvalue)
+
+OP(|, maxN | cvalue)
+REVERSE_OP(|, maxN | cvalue)
+
+COMPARE_OP(==)
+COMPARE_OP(!=)
+COMPARE_OP(< )
+COMPARE_OP(> )
+COMPARE_OP(<=)
+COMPARE_OP(>=)
+
+#undef OP
+#undef REVERSE_OP
+#undef COMPARE_OP
+
+template <uint64_t maxN, uint cvalue, typename T>
+inline constexpr Bounded<cvalue, decltype(uint() - T())>
+    operator-(BoundedConst<cvalue>, Bounded<maxN, T> value) {
+  // We allow subtraction of a variable from a constant only if the constant is greater than or
+  // equal to the maximum possible value of the variable. Since the variable could be zero, the
+  // result can be as large as the constant.
+  //
+  // We do not allow subtraction of a constant from a variable because there's never a guarantee it
+  // won't underflow (unless the constant is zero, which is silly).
+  static_assert(cvalue >= maxN, "possible underflow detected");
+  return Bounded<cvalue, decltype(uint() - T())>(cvalue - value.unwrap(), unsafe);
+}
+
+template <uint64_t aN, uint b, typename A>
+inline constexpr Bounded<kj::min(aN, b), A> min(Bounded<aN, A> a, BoundedConst<b>) {
+  return Bounded<kj::min(aN, b), A>(kj::min(b, a.unwrap()), unsafe);
+}
+template <uint64_t aN, uint b, typename A>
+inline constexpr Bounded<kj::min(aN, b), A> min(BoundedConst<b>, Bounded<aN, A> a) {
+  return Bounded<kj::min(aN, b), A>(kj::min(a.unwrap(), b), unsafe);
+}
+template <uint64_t aN, uint b, typename A>
+inline constexpr Bounded<kj::max(aN, b), A> max(Bounded<aN, A> a, BoundedConst<b>) {
+  return Bounded<kj::max(aN, b), A>(kj::max(b, a.unwrap()), unsafe);
+}
+template <uint64_t aN, uint b, typename A>
+inline constexpr Bounded<kj::max(aN, b), A> max(BoundedConst<b>, Bounded<aN, A> a) {
+  return Bounded<kj::max(aN, b), A>(kj::max(a.unwrap(), b), unsafe);
+}
+// We need to override min() between a Bounded and a constant since:
+// 1) WiderType<> might choose BoundedConst over a 1-byte Bounded, which is wrong.
+// 2) To clamp the bounds of the output type.
+// 3) Same ternary operator typechecking issues.
+
+// -------------------------------------------------------------------
+
+template <uint64_t maxN, typename T>
+class SafeUnwrapper {
+public:
+  inline explicit constexpr SafeUnwrapper(Bounded<maxN, T> value): value(value.unwrap()) {}
+
+  template <typename U, typename = EnableIf<isIntegral<U>()>>
+  inline constexpr operator U() const {
+    static_assert(maxN <= U(maxValue), "possible truncation detected");
+    return value;
+  }
+
+  inline constexpr operator bool() const {
+    static_assert(maxN <= 1, "possible truncation detected");
+    return value;
+  }
+
+private:
+  T value;
+};
+
+template <uint64_t maxN, typename T>
+inline constexpr SafeUnwrapper<maxN, T> unbound(Bounded<maxN, T> bounded) {
+  // Unwraps the bounded value, returning a value that can be implicitly cast to any integer type.
+  // If this implicit cast could truncate, a compile-time error will be raised.
+  return SafeUnwrapper<maxN, T>(bounded);
+}
+
+template <uint64_t value>
+class SafeConstUnwrapper {
+public:
+  template <typename T, typename = EnableIf<isIntegral<T>()>>
+  inline constexpr operator T() const {
+    static_assert(value <= T(maxValue), "this operation will truncate");
+    return value;
+  }
+
+  inline constexpr operator bool() const {
+    static_assert(value <= 1, "this operation will truncate");
+    return value;
+  }
+};
+
+template <uint value>
+inline constexpr SafeConstUnwrapper<value> unbound(BoundedConst<value>) {
+  return SafeConstUnwrapper<value>();
+}
+
+template <typename T, typename U>
+inline constexpr T unboundAs(U value) {
+  return unbound(value);
+}
+
+template <uint64_t requestedMax, uint64_t maxN, typename T>
+inline constexpr T unboundMax(Bounded<maxN, T> value) {
+  // Explicitly ungaurd expecting a value that is at most `maxN`.
+  static_assert(maxN <= requestedMax, "possible overflow detected");
+  return value.unwrap();
+}
+
+template <uint64_t requestedMax, uint value>
+inline constexpr uint unboundMax(BoundedConst<value>) {
+  // Explicitly ungaurd expecting a value that is at most `maxN`.
+  static_assert(value <= requestedMax, "overflow detected");
+  return value;
+}
+
+template <uint bits, typename T>
+inline constexpr auto unboundMaxBits(T value) ->
+    decltype(unboundMax<maxValueForBits<bits>()>(value)) {
+  // Explicitly ungaurd expecting a value that fits into `bits` bits.
+  return unboundMax<maxValueForBits<bits>()>(value);
+}
+
+#define OP(op) \
+template <uint64_t maxN, typename T, typename U> \
+inline constexpr auto operator op(T a, SafeUnwrapper<maxN, U> b) -> decltype(a op (T)b) { \
+  return a op (AtLeastUInt<sizeof(T)*8>)b; \
+} \
+template <uint64_t maxN, typename T, typename U> \
+inline constexpr auto operator op(SafeUnwrapper<maxN, U> b, T a) -> decltype((T)b op a) { \
+  return (AtLeastUInt<sizeof(T)*8>)b op a; \
+} \
+template <uint64_t value, typename T> \
+inline constexpr auto operator op(T a, SafeConstUnwrapper<value> b) -> decltype(a op (T)b) { \
+  return a op (AtLeastUInt<sizeof(T)*8>)b; \
+} \
+template <uint64_t value, typename T> \
+inline constexpr auto operator op(SafeConstUnwrapper<value> b, T a) -> decltype((T)b op a) { \
+  return (AtLeastUInt<sizeof(T)*8>)b op a; \
+}
+
+OP(+)
+OP(-)
+OP(*)
+OP(/)
+OP(%)
+OP(<<)
+OP(>>)
+OP(&)
+OP(|)
+OP(==)
+OP(!=)
+OP(<=)
+OP(>=)
+OP(<)
+OP(>)
+
+#undef OP
+
+// -------------------------------------------------------------------
+
+template <uint64_t maxN, typename T>
+class Range<Bounded<maxN, T>> {
+public:
+  inline constexpr Range(Bounded<maxN, T> begin, Bounded<maxN, T> end)
+      : inner(unbound(begin), unbound(end)) {}
+  inline explicit constexpr Range(Bounded<maxN, T> end)
+      : inner(unbound(end)) {}
+
+  class Iterator {
+  public:
+    Iterator() = default;
+    inline explicit Iterator(typename Range<T>::Iterator inner): inner(inner) {}
+
+    inline Bounded<maxN, T> operator* () const { return Bounded<maxN, T>(*inner, unsafe); }
+    inline Iterator& operator++() { ++inner; return *this; }
+
+    inline bool operator==(const Iterator& other) const { return inner == other.inner; }
+    inline bool operator!=(const Iterator& other) const { return inner != other.inner; }
+
+  private:
+    typename Range<T>::Iterator inner;
+  };
+
+  inline Iterator begin() const { return Iterator(inner.begin()); }
+  inline Iterator end() const { return Iterator(inner.end()); }
+
+private:
+  Range<T> inner;
+};
+
+template <typename T, typename U>
+class Range<Quantity<T, U>> {
+public:
+  inline constexpr Range(Quantity<T, U> begin, Quantity<T, U> end)
+      : inner(begin / unit<Quantity<T, U>>(), end / unit<Quantity<T, U>>()) {}
+  inline explicit constexpr Range(Quantity<T, U> end)
+      : inner(end / unit<Quantity<T, U>>()) {}
+
+  class Iterator {
+  public:
+    Iterator() = default;
+    inline explicit Iterator(typename Range<T>::Iterator inner): inner(inner) {}
+
+    inline Quantity<T, U> operator* () const { return *inner * unit<Quantity<T, U>>(); }
+    inline Iterator& operator++() { ++inner; return *this; }
+
+    inline bool operator==(const Iterator& other) const { return inner == other.inner; }
+    inline bool operator!=(const Iterator& other) const { return inner != other.inner; }
+
+  private:
+    typename Range<T>::Iterator inner;
+  };
+
+  inline Iterator begin() const { return Iterator(inner.begin()); }
+  inline Iterator end() const { return Iterator(inner.end()); }
+
+private:
+  Range<T> inner;
+};
+
+template <uint value>
+inline constexpr Range<Bounded<value, uint>> zeroTo(BoundedConst<value> end) {
+  return Range<Bounded<value, uint>>(end);
+}
+
+template <uint value, typename Unit>
+inline constexpr Range<Quantity<Bounded<value, uint>, Unit>>
+    zeroTo(Quantity<BoundedConst<value>, Unit> end) {
+  return Range<Quantity<Bounded<value, uint>, Unit>>(end);
+}
+
 }  // namespace kj
 
 #endif  // KJ_UNITS_H_