Чтение файла частями байтов, которые делятся на 6. Замените необходимые байты в каждом чанке и запишите каждый чанк в другой файл перед чтением следующего чанка.
Вы также можете попытаться выполнить чтениеследующего блока параллельно с записью следующего блока:
using( var source = new FileStream(@"c:\temp\test.txt", FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
using( var target = new FileStream(@"c:\temp\test.txt", FileMode.Open, FileAccess.Write, FileShare.ReadWrite))
{
await RewriteFile(source, target);
}
}
private async Task RewriteFile( FileStream source, FileStream target )
{
// We're reading bufferSize bytes from the source-stream inside one half of the buffer
// while the writeTask is writing the other half of the buffer to the target-stream.
// define how many chunks of 6 bytes you want to read per read operation
int chunksPerBuffer = 1;
int bufferSize = 6 * chunksPerBuffer;
// declare a byte array that contains both the bytes that are read
// and the bytes that are being written in parallel.
byte[] buffer = new byte[bufferSize * 2];
// curoff is the start-position of the bytes we're working with in the
// buffer
int curoff = 0;
Task writeTask = Task.CompletedTask;
int len;
// Read the desired number of bytes from the file into the buffer.
// In the first read operation, the bytes will be placed in the first
// half of the buffer. The next read operation will read them in
// the second half of the buffer.
while ((len = await source.ReadAsync(buffer, curoff, bufferSize).ConfigureAwait(false)) != 0)
{
// Swap the bytes in the current buffer.
// When reading x * 6 bytes in one go, every 1st byte will be replaced by the 4th byte; every 2nd byte will be replaced by the 5th byte.
for (int i = curoff; i < bufferSize + curoff; i += 6)
{
Swap(ref buffer[i], ref buffer[i + 4]);
Swap(ref buffer[i + 1], ref buffer[i + 5]);
}
// wait until the previous write-task completed.
await writeTask.ConfigureAwait(false);
// Start writing the bytes that have just been processed.
// Do not await the task here, so that the next bytes
// can be read in parallel.
writeTask = target.WriteAsync(buffer, curoff, len);
// Position the pointer to the beginnen of the other part
// in the buffer
curoff ^= bufferSize;
}
// Make sure that the last write also finishes before closing
// the target stream.
await writeTask.ConfigureAwait(false);
}
Приведенный выше код должен прочитать файл, поменять местами байты и параллельно перезаписать в тот же файл.