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 "webrtc/system_wrappers/include/aligned_malloc.h" 12 13 #include <memory.h> 14 #include <stdlib.h> 15 16 #if _WIN32 17 #include <windows.h> 18 #else 19 #include <stdint.h> 20 #endif 21 22 #include "webrtc/typedefs.h" 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 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. 35 bool ValidAlignment(size_t alignment) { 36 if (!alignment) { 37 return false; 38 } 39 return (alignment & (alignment - 1)) == 0; 40 } 41 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 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 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
