/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ /* vim: set ts=8 sts=2 et sw=2 tw=80: */ /* 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/. */ /* * Reusable template meta-functions on types and compile-time values. Meta- * functions are placed inside the 'tl' namespace to avoid conflict with non- * meta functions of the same name (e.g., mozilla::tl::FloorLog2 vs. * mozilla::FloorLog2). * * When constexpr support becomes universal, we should probably use that instead * of some of these templates, for simplicity. */ #ifndef mozilla_TemplateLib_h #define mozilla_TemplateLib_h #include <limits.h> #include <stddef.h> #include "mozilla/TypeTraits.h" namespace mozilla { namespace tl { /** Compute min/max. */ template<size_t I, size_t J> struct Min { static const size_t value = I < J ? I : J; }; template<size_t I, size_t J> struct Max { static const size_t value = I > J ? I : J; }; /** Compute floor(log2(i)). */ template<size_t I> struct FloorLog2 { static const size_t value = 1 + FloorLog2<I / 2>::value; }; template<> struct FloorLog2<0> { /* Error */ }; template<> struct FloorLog2<1> { static const size_t value = 0; }; /** Compute ceiling(log2(i)). */ template<size_t I> struct CeilingLog2 { static const size_t value = FloorLog2<2 * I - 1>::value; }; /** Round up to the nearest power of 2. */ template<size_t I> struct RoundUpPow2 { static const size_t value = size_t(1) << CeilingLog2<I>::value; }; template<> struct RoundUpPow2<0> { static const size_t value = 1; }; /** Compute the number of bits in the given unsigned type. */ template<typename T> struct BitSize { static const size_t value = sizeof(T) * CHAR_BIT; }; /** * Produce an N-bit mask, where N <= BitSize<size_t>::value. Handle the * language-undefined edge case when N = BitSize<size_t>::value. */ template<size_t N> struct NBitMask { // Assert the precondition. On success this evaluates to 0. Otherwise it // triggers divide-by-zero at compile time: a guaranteed compile error in // C++11, and usually one in C++98. Add this value to |value| to assure // its computation. static const size_t checkPrecondition = 0 / size_t(N < BitSize<size_t>::value); static const size_t value = (size_t(1) << N) - 1 + checkPrecondition; }; template<> struct NBitMask<BitSize<size_t>::value> { static const size_t value = size_t(-1); }; /** * For the unsigned integral type size_t, compute a mask M for N such that * for all X, !(X & M) implies X * N will not overflow (w.r.t size_t) */ template<size_t N> struct MulOverflowMask { static const size_t value = ~NBitMask<BitSize<size_t>::value - CeilingLog2<N>::value>::value; }; template<> struct MulOverflowMask<0> { /* Error */ }; template<> struct MulOverflowMask<1> { static const size_t value = 0; }; /** * And<bool...> computes the logical 'and' of its argument booleans. * * Examples: * mozilla::t1::And<true, true>::value is true. * mozilla::t1::And<true, false>::value is false. * mozilla::t1::And<>::value is true. */ template<bool...> struct And; template<> struct And<> : public TrueType { }; template<bool C1, bool... Cn> struct And<C1, Cn...> : public Conditional<C1, And<Cn...>, FalseType>::Type { }; } // namespace tl } // namespace mozilla #endif /* mozilla_TemplateLib_h */