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Use Span<byte> to read BAT in VirtualPC disk images, making it up to 38 times faster.

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Natalia Portillo
2019-03-12 01:01:54 +00:00
parent b076186e93
commit 79bfe67f41
1 changed files with 10 additions and 38 deletions
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48
DiscImageChef.DiscImages/VHD/Read.cs
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@@ -32,6 +32,7 @@
using System;
using System.IO;
using System.Runtime.InteropServices;
using System.Text;
using DiscImageChef.Checksums;
using DiscImageChef.CommonTypes;
@@ -39,7 +40,6 @@ using DiscImageChef.CommonTypes.Enums;
using DiscImageChef.CommonTypes.Exceptions;
using DiscImageChef.CommonTypes.Interfaces;
using DiscImageChef.Console;
using DiscImageChef.Helpers;
namespace DiscImageChef.DiscImages
{
@@ -399,51 +399,23 @@ namespace DiscImageChef.DiscImages
blockAllocationTable = new uint[thisDynamic.MaxTableEntries];
// Safe and slow code. It takes 76,572 ms to fill a 30720 entries BAT
/*
byte[] bat = new byte[thisDynamic.maxTableEntries * 4];
imageStream.Seek((long)thisDynamic.tableOffset, SeekOrigin.Begin);
imageStream.Read(bat, 0, (int)(thisDynamic.maxTableEntries * 4));
for (int i = 0; i < thisDynamic.maxTableEntries; i++)
blockAllocationTable[i] = BigEndianBitConverter.ToUInt32(bat, 4 * i);
DateTime endTime = DateTime.UtcNow;
DicConsole.DebugWriteLine("VirtualPC plugin", "Filling the BAT took {0} seconds", (endTime-startTime).TotalSeconds);
*/
// How many sectors uses the BAT
uint batSectorCount = (uint)Math.Ceiling((double)thisDynamic.MaxTableEntries * 4 / 512);
int batSectorCount = (int)Math.Ceiling((double)thisDynamic.MaxTableEntries * 4 / 512);
byte[] batSectorBytes = new byte[512];
byte[] bat = new byte[thisDynamic.MaxTableEntries * 4];
imageStream.Seek((long)thisDynamic.TableOffset, SeekOrigin.Begin);
imageStream.Read(bat, 0, batSectorCount);
// Unsafe and fast code. It takes 4 ms to fill a 30720 entries BAT
for(int i = 0; i < batSectorCount; i++)
{
imageStream.Seek((long)thisDynamic.TableOffset + i * 512, SeekOrigin.Begin);
imageStream.Read(batSectorBytes, 0, 512);
// This does the big-endian trick but reverses the order of elements also
Array.Reverse(batSectorBytes);
BatSector batSector = Marshal.ByteArrayToStructureLittleEndian<BatSector>(batSectorBytes);
// This restores the order of elements
Array.Reverse(batSector.blockPointer);
if(blockAllocationTable.Length >= i * 512 / 4 + 512 / 4)
Array.Copy(batSector.blockPointer, 0, blockAllocationTable, i * 512 / 4, 512 / 4);
else
Array.Copy(batSector.blockPointer, 0, blockAllocationTable, i * 512 / 4,
blockAllocationTable.Length - i * 512 / 4);
}
ReadOnlySpan<byte> span = bat;
blockAllocationTable =
MemoryMarshal.Cast<byte, uint>(span).Slice(0, (int)thisDynamic.MaxTableEntries).ToArray();
for(int i = 0; i < blockAllocationTable.Length; i++)
blockAllocationTable[i] = Swapping.Swap(blockAllocationTable[i]);
DateTime endTime = DateTime.UtcNow;
DicConsole.DebugWriteLine("VirtualPC plugin", "Filling the BAT took {0} seconds",
(endTime - startTime).TotalSeconds);
// Too noisy
/*
for (int i = 0; i < thisDynamic.maxTableEntries; i++)
DicConsole.DebugWriteLine("VirtualPC plugin", "blockAllocationTable[{0}] = {1}", i, blockAllocationTable[i]);
*/
// Get the roundest number of sectors needed to store the block bitmap
bitmapSize = (uint)Math.Ceiling((double)thisDynamic.BlockSize / 512
// 1 bit per sector on the bitmap
/ 8