Source/JavaScriptCore/wtf/StdLibExtras.h

/*
 * Copyright (C) 2008 Apple Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

#ifndef WTF_StdLibExtras_h
#define WTF_StdLibExtras_h

#include <wtf/Assertions.h>

// Use these to declare and define a static local variable (static T;) so that
//  it is leaked so that its destructors are not called at exit. Using this
//  macro also allows workarounds a compiler bug present in Apple's version of GCC 4.0.1.
#ifndef DEFINE_STATIC_LOCAL
#if COMPILER(GCC) && defined(__APPLE_CC__) && __GNUC__ == 4 && __GNUC_MINOR__ == 0 && __GNUC_PATCHLEVEL__ == 1
#define DEFINE_STATIC_LOCAL(type, name, arguments) \
    static type* name##Ptr = new type arguments; \
    type& name = *name##Ptr
#else
#define DEFINE_STATIC_LOCAL(type, name, arguments) \
    static type& name = *new type arguments
#endif
#endif

// OBJECT_OFFSETOF: Like the C++ offsetof macro, but you can use it with classes.
// The magic number 0x4000 is insignificant. We use it to avoid using NULL, since
// NULL can cause compiler problems, especially in cases of multiple inheritance.
#define OBJECT_OFFSETOF(class, field) (reinterpret_cast<ptrdiff_t>(&(reinterpret_cast<class*>(0x4000)->field)) - 0x4000)

// STRINGIZE: Can convert any value to quoted string, even expandable macros
#define STRINGIZE(exp) #exp
#define STRINGIZE_VALUE_OF(exp) STRINGIZE(exp)

/*
 * The reinterpret_cast<Type1*>([pointer to Type2]) expressions - where
 * sizeof(Type1) > sizeof(Type2) - cause the following warning on ARM with GCC:
 * increases required alignment of target type.
 *
 * An implicit or an extra static_cast<void*> bypasses the warning.
 * For more info see the following bugzilla entries:
 * - https://bugs.webkit.org/show_bug.cgi?id=38045
 * - http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43976
 */
#if (CPU(ARM) || CPU(MIPS)) && COMPILER(GCC)
template<typename Type>
bool isPointerTypeAlignmentOkay(Type* ptr)
{
    return !(reinterpret_cast<intptr_t>(ptr) % __alignof__(Type));
}

template<typename TypePtr>
TypePtr reinterpret_cast_ptr(void* ptr)
{
    ASSERT(isPointerTypeAlignmentOkay(reinterpret_cast<TypePtr>(ptr)));
    return reinterpret_cast<TypePtr>(ptr);
}

template<typename TypePtr>
TypePtr reinterpret_cast_ptr(const void* ptr)
{
    ASSERT(isPointerTypeAlignmentOkay(reinterpret_cast<TypePtr>(ptr)));
    return reinterpret_cast<TypePtr>(ptr);
}
#else
#define reinterpret_cast_ptr reinterpret_cast
#endif

namespace WTF {

/*
 * C++'s idea of a reinterpret_cast lacks sufficient cojones.
 */
template<typename TO, typename FROM>
inline TO bitwise_cast(FROM from)
{
    COMPILE_ASSERT(sizeof(TO) == sizeof(FROM), WTF_bitwise_cast_sizeof_casted_types_is_equal);
    union {
        FROM from;
        TO to;
    } u;
    u.from = from;
    return u.to;
}

// Returns a count of the number of bits set in 'bits'.
inline size_t bitCount(unsigned bits)
{
    bits = bits - ((bits >> 1) & 0x55555555);
    bits = (bits & 0x33333333) + ((bits >> 2) & 0x33333333);
    return (((bits + (bits >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24;
}

// Macro that returns a compile time constant with the length of an array, but gives an error if passed a non-array.
template<typename T, size_t Size> char (&ArrayLengthHelperFunction(T (&)[Size]))[Size];
#define WTF_ARRAY_LENGTH(array) sizeof(::WTF::ArrayLengthHelperFunction(array))

// Efficient implementation that takes advantage of powers of two.
template<size_t divisor> inline size_t roundUpToMultipleOf(size_t x)
{
    COMPILE_ASSERT(divisor && !(divisor & (divisor - 1)), divisor_is_a_power_of_two);

    size_t remainderMask = divisor - 1;
    return (x + remainderMask) & ~remainderMask;
}

// Binary search algorithm, calls extractKey on pre-sorted elements in array,
// compares result with key (KeyTypes should be comparable with '--', '<', '>').
// Optimized for cases where the array contains the key, checked by assertions.
template<typename ArrayType, typename KeyType, KeyType(*extractKey)(ArrayType*)>
inline ArrayType* binarySearch(ArrayType* array, size_t size, KeyType key)
{
    // The array must contain at least one element (pre-condition, array does conatin key).
    // If the array only contains one element, no need to do the comparison.
    while (size > 1) {
        // Pick an element to check, half way through the array, and read the value.
        int pos = (size - 1) >> 1;
        KeyType val = extractKey(&array[pos]);
        
        // If the key matches, success!
        if (val == key)
            return &array[pos];
        // The item we are looking for is smaller than the item being check; reduce the value of 'size',
        // chopping off the right hand half of the array.
        else if (key < val)
            size = pos;
        // Discard all values in the left hand half of the array, up to and including the item at pos.
        else {
            size -= (pos + 1);
            array += (pos + 1);
        }

        // 'size' should never reach zero.
        ASSERT(size);
    }
    
    // If we reach this point we've chopped down to one element, no need to check it matches
    ASSERT(size == 1);
    ASSERT(key == extractKey(&array[0]));
    return &array[0];
}

} // namespace WTF

using WTF::binarySearch;
using WTF::bitwise_cast;

#endif // WTF_StdLibExtras_h