StdLibExtras.h revision 2bde8e466a4451c7319e3a072d118917957d6554 
1/*
2 * Copyright (C) 2008 Apple Inc. All Rights Reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 *    notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 *    notice, this list of conditions and the following disclaimer in the
11 *    documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
14 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
17 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
18 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
19 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
20 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
21 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
23 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#ifndef WTF_StdLibExtras_h
27#define WTF_StdLibExtras_h
28
29#include <wtf/Assertions.h>
30
31// Use these to declare and define a static local variable (static T;) so that
32//  it is leaked so that its destructors are not called at exit. Using this
33//  macro also allows workarounds a compiler bug present in Apple's version of GCC 4.0.1.
34#ifndef DEFINE_STATIC_LOCAL
35#if COMPILER(GCC) && defined(__APPLE_CC__) && __GNUC__ == 4 && __GNUC_MINOR__ == 0 && __GNUC_PATCHLEVEL__ == 1
36#define DEFINE_STATIC_LOCAL(type, name, arguments) \
37    static type* name##Ptr = new type arguments; \
38    type& name = *name##Ptr
39#else
40#define DEFINE_STATIC_LOCAL(type, name, arguments) \
41    static type& name = *new type arguments
42#endif
43#endif
44
45// OBJECT_OFFSETOF: Like the C++ offsetof macro, but you can use it with classes.
46// The magic number 0x4000 is insignificant. We use it to avoid using NULL, since
47// NULL can cause compiler problems, especially in cases of multiple inheritance.
48#define OBJECT_OFFSETOF(class, field) (reinterpret_cast<ptrdiff_t>(&(reinterpret_cast<class*>(0x4000)->field)) - 0x4000)
49
50// STRINGIZE: Can convert any value to quoted string, even expandable macros
51#define STRINGIZE(exp) #exp
52#define STRINGIZE_VALUE_OF(exp) STRINGIZE(exp)
53
54/*
55 * The reinterpret_cast<Type1*>([pointer to Type2]) expressions - where
56 * sizeof(Type1) > sizeof(Type2) - cause the following warning on ARM with GCC:
57 * increases required alignment of target type.
58 *
59 * An implicit or an extra static_cast<void*> bypasses the warning.
60 * For more info see the following bugzilla entries:
61 * - https://bugs.webkit.org/show_bug.cgi?id=38045
62 * - http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43976
63 */
64#if (CPU(ARM) || CPU(MIPS)) && COMPILER(GCC)
65template<typename Type>
66bool isPointerTypeAlignmentOkay(Type* ptr)
67{
68    return !(reinterpret_cast<intptr_t>(ptr) % __alignof__(Type));
69}
70
71template<typename TypePtr>
72TypePtr reinterpret_cast_ptr(void* ptr)
73{
74    ASSERT(isPointerTypeAlignmentOkay(reinterpret_cast<TypePtr>(ptr)));
75    return reinterpret_cast<TypePtr>(ptr);
76}
77
78template<typename TypePtr>
79TypePtr reinterpret_cast_ptr(const void* ptr)
80{
81    ASSERT(isPointerTypeAlignmentOkay(reinterpret_cast<TypePtr>(ptr)));
82    return reinterpret_cast<TypePtr>(ptr);
83}
84#else
85#define reinterpret_cast_ptr reinterpret_cast
86#endif
87
88namespace WTF {
89
90/*
91 * C++'s idea of a reinterpret_cast lacks sufficient cojones.
92 */
93template<typename TO, typename FROM>
94inline TO bitwise_cast(FROM from)
95{
96    COMPILE_ASSERT(sizeof(TO) == sizeof(FROM), WTF_bitwise_cast_sizeof_casted_types_is_equal);
97    union {
98        FROM from;
99        TO to;
100    } u;
101    u.from = from;
102    return u.to;
103}
104
105// Returns a count of the number of bits set in 'bits'.
106inline size_t bitCount(unsigned bits)
107{
108    bits = bits - ((bits >> 1) & 0x55555555);
109    bits = (bits & 0x33333333) + ((bits >> 2) & 0x33333333);
110    return (((bits + (bits >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24;
111}
112
113// Macro that returns a compile time constant with the length of an array, but gives an error if passed a non-array.
114template<typename T, size_t Size> char (&ArrayLengthHelperFunction(T (&)[Size]))[Size];
115#define WTF_ARRAY_LENGTH(array) sizeof(::WTF::ArrayLengthHelperFunction(array))
116
117// Efficient implementation that takes advantage of powers of two.
118template<size_t divisor> inline size_t roundUpToMultipleOf(size_t x)
119{
120    COMPILE_ASSERT(divisor && !(divisor & (divisor - 1)), divisor_is_a_power_of_two);
121
122    size_t remainderMask = divisor - 1;
123    return (x + remainderMask) & ~remainderMask;
124}
125
126// Binary search algorithm, calls extractKey on pre-sorted elements in array,
127// compares result with key (KeyTypes should be comparable with '--', '<', '>').
128// Optimized for cases where the array contains the key, checked by assertions.
129template<typename ArrayType, typename KeyType, KeyType(*extractKey)(ArrayType*)>
130inline ArrayType* binarySearch(ArrayType* array, size_t size, KeyType key)
131{
132    // The array must contain at least one element (pre-condition, array does conatin key).
133    // If the array only contains one element, no need to do the comparison.
134    while (size > 1) {
135        // Pick an element to check, half way through the array, and read the value.
136        int pos = (size - 1) >> 1;
137        KeyType val = extractKey(&array[pos]);
138
139        // If the key matches, success!
140        if (val == key)
141            return &array[pos];
142        // The item we are looking for is smaller than the item being check; reduce the value of 'size',
143        // chopping off the right hand half of the array.
144        else if (key < val)
145            size = pos;
146        // Discard all values in the left hand half of the array, up to and including the item at pos.
147        else {
148            size -= (pos + 1);
149            array += (pos + 1);
150        }
151
152        // 'size' should never reach zero.
153        ASSERT(size);
154    }
155
156    // If we reach this point we've chopped down to one element, no need to check it matches
157    ASSERT(size == 1);
158    ASSERT(key == extractKey(&array[0]));
159    return &array[0];
160}
161
162} // namespace WTF
163
164using WTF::binarySearch;
165
166#endif // WTF_StdLibExtras_h
167