1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
|
/*
* Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "rtc_base/memory/aligned_malloc.h"
#include <stdlib.h> // for free, malloc
#include <string.h> // for memcpy
#include "rtc_base/checks.h"
#ifdef _WIN32
#include <windows.h>
#else
#include <stdint.h>
#endif
// Reference on memory alignment:
// http://stackoverflow.com/questions/227897/solve-the-memory-alignment-in-c-interview-question-that-stumped-me
namespace webrtc {
uintptr_t GetRightAlign(uintptr_t start_pos, size_t alignment) {
// The pointer should be aligned with `alignment` bytes. The - 1 guarantees
// that it is aligned towards the closest higher (right) address.
return (start_pos + alignment - 1) & ~(alignment - 1);
}
// Alignment must be an integer power of two.
bool ValidAlignment(size_t alignment) {
if (!alignment) {
return false;
}
return (alignment & (alignment - 1)) == 0;
}
void* GetRightAlign(const void* pointer, size_t alignment) {
if (!pointer) {
return nullptr;
}
if (!ValidAlignment(alignment)) {
return nullptr;
}
uintptr_t start_pos = reinterpret_cast<uintptr_t>(pointer);
return reinterpret_cast<void*>(GetRightAlign(start_pos, alignment));
}
void* AlignedMalloc(size_t size, size_t alignment) {
if (size == 0) {
return nullptr;
}
if (!ValidAlignment(alignment)) {
return nullptr;
}
// The memory is aligned towards the lowest address that so only
// alignment - 1 bytes needs to be allocated.
// A pointer to the start of the memory must be stored so that it can be
// retreived for deletion, ergo the sizeof(uintptr_t).
void* memory_pointer = malloc(size + sizeof(uintptr_t) + alignment - 1);
RTC_CHECK(memory_pointer) << "Couldn't allocate memory in AlignedMalloc";
// Aligning after the sizeof(uintptr_t) bytes will leave room for the header
// in the same memory block.
uintptr_t align_start_pos = reinterpret_cast<uintptr_t>(memory_pointer);
align_start_pos += sizeof(uintptr_t);
uintptr_t aligned_pos = GetRightAlign(align_start_pos, alignment);
void* aligned_pointer = reinterpret_cast<void*>(aligned_pos);
// Store the address to the beginning of the memory just before the aligned
// memory.
uintptr_t header_pos = aligned_pos - sizeof(uintptr_t);
void* header_pointer = reinterpret_cast<void*>(header_pos);
uintptr_t memory_start = reinterpret_cast<uintptr_t>(memory_pointer);
memcpy(header_pointer, &memory_start, sizeof(uintptr_t));
return aligned_pointer;
}
void AlignedFree(void* mem_block) {
if (mem_block == nullptr) {
return;
}
uintptr_t aligned_pos = reinterpret_cast<uintptr_t>(mem_block);
uintptr_t header_pos = aligned_pos - sizeof(uintptr_t);
// Read out the address of the AlignedMemory struct from the header.
uintptr_t memory_start_pos = *reinterpret_cast<uintptr_t*>(header_pos);
void* memory_start = reinterpret_cast<void*>(memory_start_pos);
free(memory_start);
}
} // namespace webrtc
|
