gecko/js/public/TemplateLib.h
Jeff Walden 7f153524ef Bug 711672 - Break mfbt's dependency on jstypes.h by moving various API macros out of JS and into mfbt. r=luke, r=cjones
--HG--
extra : rebase_source : f18993e1eec1a5e5bcdb9cd97fa7d7c6ad261e2c
2011-12-13 14:26:58 -05:00

180 lines
7.2 KiB
C++

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* vim: set ts=8 sw=4 et tw=99 ft=cpp:
*
* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Mozilla SpiderMonkey JavaScript code.
*
* The Initial Developer of the Original Code is
* the Mozilla Foundation.
* Portions created by the Initial Developer are Copyright (C) 2011
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Luke Wagner <luke@mozilla.com>
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#ifndef js_template_lib_h__
#define js_template_lib_h__
#include "jstypes.h"
/*
* Library of reusable template meta-functions (that is, functions on types and
* compile-time values). Meta-functions are placed inside the 'tl' namespace to
* avoid conflict with non-meta functions that logically have the same name
* (e.g., js::tl::Min vs. js::Min).
*/
namespace js {
namespace tl {
/* Compute min/max/clamp. */
template <size_t i, size_t j> struct Min {
static const size_t result = i < j ? i : j;
};
template <size_t i, size_t j> struct Max {
static const size_t result = i > j ? i : j;
};
template <size_t i, size_t min, size_t max> struct Clamp {
static const size_t result = i < min ? min : (i > max ? max : i);
};
/* Compute x^y. */
template <size_t x, size_t y> struct Pow {
static const size_t result = x * Pow<x, y - 1>::result;
};
template <size_t x> struct Pow<x,0> {
static const size_t result = 1;
};
/* Compute floor(log2(i)). */
template <size_t i> struct FloorLog2 {
static const size_t result = 1 + FloorLog2<i / 2>::result;
};
template <> struct FloorLog2<0> { /* Error */ };
template <> struct FloorLog2<1> { static const size_t result = 0; };
/* Compute ceiling(log2(i)). */
template <size_t i> struct CeilingLog2 {
static const size_t result = FloorLog2<2 * i - 1>::result;
};
/* Round up to the nearest power of 2. */
template <size_t i> struct RoundUpPow2 {
static const size_t result = size_t(1) << CeilingLog2<i>::result;
};
template <> struct RoundUpPow2<0> {
static const size_t result = 1;
};
/* Compute the number of bits in the given unsigned type. */
template <class T> struct BitSize {
static const size_t result = sizeof(T) * JS_BITS_PER_BYTE;
};
/* Allow Assertions by only including the 'result' typedef if 'true'. */
template <bool> struct StaticAssert {};
template <> struct StaticAssert<true> { typedef int result; };
/* Boolean test for whether two types are the same. */
template <class T, class U> struct IsSameType {
static const bool result = false;
};
template <class T> struct IsSameType<T,T> {
static const bool result = true;
};
/*
* Produce an N-bit mask, where N <= BitSize<size_t>::result. Handle the
* language-undefined edge case when N = BitSize<size_t>::result.
*/
template <size_t N> struct NBitMask {
typedef typename StaticAssert<N < BitSize<size_t>::result>::result _;
static const size_t result = (size_t(1) << N) - 1;
};
template <> struct NBitMask<BitSize<size_t>::result> {
static const size_t result = 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 result =
~NBitMask<BitSize<size_t>::result - CeilingLog2<N>::result>::result;
};
template <> struct MulOverflowMask<0> { /* Error */ };
template <> struct MulOverflowMask<1> { static const size_t result = 0; };
/*
* Generate a mask for T such that if (X & sUnsafeRangeSizeMask), an X-sized
* array of T's is big enough to cause a ptrdiff_t overflow when subtracting
* a pointer to the end of the array from the beginning.
*/
template <class T> struct UnsafeRangeSizeMask {
/*
* The '2' factor means the top bit is clear, sizeof(T) converts from
* units of elements to bytes.
*/
static const size_t result = MulOverflowMask<2 * sizeof(T)>::result;
};
/* Return T stripped of any const-ness. */
template <class T> struct StripConst { typedef T result; };
template <class T> struct StripConst<const T> { typedef T result; };
/*
* Traits class for identifying POD types. Until C++0x, there is no automatic
* way to detect PODs, so for the moment it is done manually.
*/
template <class T> struct IsPodType { static const bool result = false; };
template <> struct IsPodType<char> { static const bool result = true; };
template <> struct IsPodType<signed char> { static const bool result = true; };
template <> struct IsPodType<unsigned char> { static const bool result = true; };
template <> struct IsPodType<short> { static const bool result = true; };
template <> struct IsPodType<unsigned short> { static const bool result = true; };
template <> struct IsPodType<int> { static const bool result = true; };
template <> struct IsPodType<unsigned int> { static const bool result = true; };
template <> struct IsPodType<long> { static const bool result = true; };
template <> struct IsPodType<unsigned long> { static const bool result = true; };
template <> struct IsPodType<long long> { static const bool result = true; };
template <> struct IsPodType<unsigned long long> { static const bool result = true; };
template <> struct IsPodType<float> { static const bool result = true; };
template <> struct IsPodType<double> { static const bool result = true; };
template <> struct IsPodType<wchar_t> { static const bool result = true; };
template <typename T> struct IsPodType<T *> { static const bool result = true; };
template <bool cond, typename T, T v1, T v2> struct If { static const T result = v1; };
template <typename T, T v1, T v2> struct If<false, T, v1, v2> { static const T result = v2; };
} /* namespace tl */
} /* namespace js */
#endif /* js_template_lib_h__ */