1 /*
2 * Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
10
11 #include "system_wrappers/include/aligned_malloc.h"
12
13 #include <memory.h>
14 #include <stdlib.h>
15
16 #ifdef _WIN32
17 #include <windows.h>
18 #else
19 #include <stdint.h>
20 #endif
21
22 #include "typedefs.h" // NOLINT(build/include)
23
24 // Reference on memory alignment:
25 // http://stackoverflow.com/questions/227897/solve-the-memory-alignment-in-c-interview-question-that-stumped-me
26 namespace webrtc {
27
GetRightAlign(uintptr_t start_pos,size_t alignment)28 uintptr_t GetRightAlign(uintptr_t start_pos, size_t alignment) {
29 // The pointer should be aligned with |alignment| bytes. The - 1 guarantees
30 // that it is aligned towards the closest higher (right) address.
31 return (start_pos + alignment - 1) & ~(alignment - 1);
32 }
33
34 // Alignment must be an integer power of two.
ValidAlignment(size_t alignment)35 bool ValidAlignment(size_t alignment) {
36 if (!alignment) {
37 return false;
38 }
39 return (alignment & (alignment - 1)) == 0;
40 }
41
GetRightAlign(const void * pointer,size_t alignment)42 void* GetRightAlign(const void* pointer, size_t alignment) {
43 if (!pointer) {
44 return NULL;
45 }
46 if (!ValidAlignment(alignment)) {
47 return NULL;
48 }
49 uintptr_t start_pos = reinterpret_cast<uintptr_t>(pointer);
50 return reinterpret_cast<void*>(GetRightAlign(start_pos, alignment));
51 }
52
AlignedMalloc(size_t size,size_t alignment)53 void* AlignedMalloc(size_t size, size_t alignment) {
54 if (size == 0) {
55 return NULL;
56 }
57 if (!ValidAlignment(alignment)) {
58 return NULL;
59 }
60
61 // The memory is aligned towards the lowest address that so only
62 // alignment - 1 bytes needs to be allocated.
63 // A pointer to the start of the memory must be stored so that it can be
64 // retreived for deletion, ergo the sizeof(uintptr_t).
65 void* memory_pointer = malloc(size + sizeof(uintptr_t) + alignment - 1);
66 if (memory_pointer == NULL) {
67 return NULL;
68 }
69
70 // Aligning after the sizeof(uintptr_t) bytes will leave room for the header
71 // in the same memory block.
72 uintptr_t align_start_pos = reinterpret_cast<uintptr_t>(memory_pointer);
73 align_start_pos += sizeof(uintptr_t);
74 uintptr_t aligned_pos = GetRightAlign(align_start_pos, alignment);
75 void* aligned_pointer = reinterpret_cast<void*>(aligned_pos);
76
77 // Store the address to the beginning of the memory just before the aligned
78 // memory.
79 uintptr_t header_pos = aligned_pos - sizeof(uintptr_t);
80 void* header_pointer = reinterpret_cast<void*>(header_pos);
81 uintptr_t memory_start = reinterpret_cast<uintptr_t>(memory_pointer);
82 memcpy(header_pointer, &memory_start, sizeof(uintptr_t));
83
84 return aligned_pointer;
85 }
86
AlignedFree(void * mem_block)87 void AlignedFree(void* mem_block) {
88 if (mem_block == NULL) {
89 return;
90 }
91 uintptr_t aligned_pos = reinterpret_cast<uintptr_t>(mem_block);
92 uintptr_t header_pos = aligned_pos - sizeof(uintptr_t);
93
94 // Read out the address of the AlignedMemory struct from the header.
95 uintptr_t memory_start_pos = *reinterpret_cast<uintptr_t*>(header_pos);
96 void* memory_start = reinterpret_cast<void*>(memory_start_pos);
97 free(memory_start);
98 }
99
100 } // namespace webrtc
101