Line data    Source code

       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             : #ifdef _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           0 : 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           0 :   return (start_pos + alignment - 1) & ~(alignment - 1);
      32             : }
      33             : 
      34             : // Alignment must be an integer power of two.
      35           0 : bool ValidAlignment(size_t alignment) {
      36           0 :   if (!alignment) {
      37           0 :     return false;
      38             :   }
      39           0 :   return (alignment & (alignment - 1)) == 0;
      40             : }
      41             : 
      42           0 : void* GetRightAlign(const void* pointer, size_t alignment) {
      43           0 :   if (!pointer) {
      44           0 :     return NULL;
      45             :   }
      46           0 :   if (!ValidAlignment(alignment)) {
      47           0 :     return NULL;
      48             :   }
      49           0 :   uintptr_t start_pos = reinterpret_cast<uintptr_t>(pointer);
      50           0 :   return reinterpret_cast<void*>(GetRightAlign(start_pos, alignment));
      51             : }
      52             : 
      53           0 : void* AlignedMalloc(size_t size, size_t alignment) {
      54           0 :   if (size == 0) {
      55           0 :     return NULL;
      56             :   }
      57           0 :   if (!ValidAlignment(alignment)) {
      58           0 :     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           0 :   void* memory_pointer = malloc(size + sizeof(uintptr_t) + alignment - 1);
      66           0 :   if (memory_pointer == NULL) {
      67           0 :     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           0 :   uintptr_t align_start_pos = reinterpret_cast<uintptr_t>(memory_pointer);
      73           0 :   align_start_pos += sizeof(uintptr_t);
      74           0 :   uintptr_t aligned_pos = GetRightAlign(align_start_pos, alignment);
      75           0 :   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           0 :   uintptr_t header_pos = aligned_pos - sizeof(uintptr_t);
      80           0 :   void* header_pointer = reinterpret_cast<void*>(header_pos);
      81           0 :   uintptr_t memory_start = reinterpret_cast<uintptr_t>(memory_pointer);
      82           0 :   memcpy(header_pointer, &memory_start, sizeof(uintptr_t));
      83             : 
      84           0 :   return aligned_pointer;
      85             : }
      86             : 
      87           0 : void AlignedFree(void* mem_block) {
      88           0 :   if (mem_block == NULL) {
      89           0 :     return;
      90             :   }
      91           0 :   uintptr_t aligned_pos = reinterpret_cast<uintptr_t>(mem_block);
      92           0 :   uintptr_t header_pos = aligned_pos - sizeof(uintptr_t);
      93             : 
      94             :   // Read out the address of the AlignedMemory struct from the header.
      95           0 :   uintptr_t memory_start_pos = *reinterpret_cast<uintptr_t*>(header_pos);
      96           0 :   void* memory_start = reinterpret_cast<void*>(memory_start_pos);
      97           0 :   free(memory_start);
      98             : }
      99             : 
     100             : }  // namespace webrtc