99 lines
3.2 KiB
C++
99 lines
3.2 KiB
C++
/*
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* Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "rtc_base/memory/aligned_malloc.h"
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#include <stdlib.h> // for free, malloc
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#include <string.h> // for memcpy
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#ifdef _WIN32
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#include <windows.h>
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#else
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#include <stdint.h>
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#endif
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// Reference on memory alignment:
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// http://stackoverflow.com/questions/227897/solve-the-memory-alignment-in-c-interview-question-that-stumped-me
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namespace webrtc {
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uintptr_t GetRightAlign(uintptr_t start_pos, size_t alignment) {
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// The pointer should be aligned with |alignment| bytes. The - 1 guarantees
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// that it is aligned towards the closest higher (right) address.
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return (start_pos + alignment - 1) & ~(alignment - 1);
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}
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// Alignment must be an integer power of two.
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bool ValidAlignment(size_t alignment) {
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if (!alignment) {
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return false;
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}
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return (alignment & (alignment - 1)) == 0;
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}
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void* GetRightAlign(const void* pointer, size_t alignment) {
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if (!pointer) {
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return NULL;
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}
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if (!ValidAlignment(alignment)) {
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return NULL;
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}
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uintptr_t start_pos = reinterpret_cast<uintptr_t>(pointer);
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return reinterpret_cast<void*>(GetRightAlign(start_pos, alignment));
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}
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void* AlignedMalloc(size_t size, size_t alignment) {
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if (size == 0) {
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return NULL;
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}
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if (!ValidAlignment(alignment)) {
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return NULL;
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}
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// The memory is aligned towards the lowest address that so only
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// alignment - 1 bytes needs to be allocated.
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// A pointer to the start of the memory must be stored so that it can be
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// retreived for deletion, ergo the sizeof(uintptr_t).
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void* memory_pointer = malloc(size + sizeof(uintptr_t) + alignment - 1);
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if (memory_pointer == NULL) {
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return NULL;
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}
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// Aligning after the sizeof(uintptr_t) bytes will leave room for the header
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// in the same memory block.
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uintptr_t align_start_pos = reinterpret_cast<uintptr_t>(memory_pointer);
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align_start_pos += sizeof(uintptr_t);
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uintptr_t aligned_pos = GetRightAlign(align_start_pos, alignment);
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void* aligned_pointer = reinterpret_cast<void*>(aligned_pos);
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// Store the address to the beginning of the memory just before the aligned
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// memory.
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uintptr_t header_pos = aligned_pos - sizeof(uintptr_t);
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void* header_pointer = reinterpret_cast<void*>(header_pos);
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uintptr_t memory_start = reinterpret_cast<uintptr_t>(memory_pointer);
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memcpy(header_pointer, &memory_start, sizeof(uintptr_t));
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return aligned_pointer;
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}
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void AlignedFree(void* mem_block) {
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if (mem_block == NULL) {
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return;
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}
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uintptr_t aligned_pos = reinterpret_cast<uintptr_t>(mem_block);
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uintptr_t header_pos = aligned_pos - sizeof(uintptr_t);
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// Read out the address of the AlignedMemory struct from the header.
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uintptr_t memory_start_pos = *reinterpret_cast<uintptr_t*>(header_pos);
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void* memory_start = reinterpret_cast<void*>(memory_start_pos);
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free(memory_start);
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}
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} // namespace webrtc
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