I'm trying to load some decimal values from a file but I can't work out the correct way to take the raw values and convert them into decimals.
I've read the file out into a byte array, and each chunk of four bytes is supposed to represent one decimal value. To help figure it out, I've constructed a table of how the decimal values 1 through to 46 are represented as four byte chunks.
For instance, the number 1 appears as 0,0,128,63 the number 2 as 0,0,0,64 and so on up to 46, which is 0,0,56,66. The full table is available here .
There is also another series of numbers which go to three decimal places and include negatives, which is here .
The only documentation I have states
They are stored least significant byte first: 1's, 256's, 65536's, 16777216's. This makes the hex sequence 01 01 00 00 into the number 257 (decimal). In C/C++, to read eg a float, do: float x; fread(&x, sizeof(float), 1, fileptr);
However I'm using .NET's File.ReadAllBytes method so this isn't much help. If anyone can spare a few minutes to look at the examples files and see if they can spot a way to convert the values to decimals I'd be most grateful.
You can use BitConverter.ToSingle to read a float value from a byte array, so to get a sequence of floats, you could do something like this:
byte[] data = File.ReadAllBytes(fileName);
int count = data.Length / 4;
Debug.Assert(data.Length % 4 == 0);
IEnumerable<float> values = Enumerable.Range(0, count)
.Select(i => BitConverter.ToSingle(data, i*4));
Have you looked into using the BitConverter class? It converts between byte arrays and various types.
Edit: MSDN has a helpful comment on the documentation for BitConverter at http://msdn.microsoft.com/en-us/library/system.bitconverter_methods(v=vs.85).aspx :
public static decimal ToDecimal(byte[] bytes)
{
int[] bits = new int[4];
bits[0] = ((bytes[0] | (bytes[1] << 8)) | (bytes[2] << 0x10)) | (bytes[3] << 0x18); //lo
bits[1] = ((bytes[4] | (bytes[5] << 8)) | (bytes[6] << 0x10)) | (bytes[7] << 0x18); //mid
bits[2] = ((bytes[8] | (bytes[9] << 8)) | (bytes[10] << 0x10)) | (bytes[11] << 0x18); //hi
bits[3] = ((bytes[12] | (bytes[13] << 8)) | (bytes[14] << 0x10)) | (bytes[15] << 0x18); //flags
return new decimal(bits);
}
public static byte[] GetBytes(decimal d)
{
byte[] bytes = new byte[16];
int[] bits = decimal.GetBits(d);
int lo = bits[0];
int mid = bits[1];
int hi = bits[2];
int flags = bits[3];
bytes[0] = (byte)lo;
bytes[1] = (byte)(lo >> 8);
bytes[2] = (byte)(lo >> 0x10);
bytes[3] = (byte)(lo >> 0x18);
bytes[4] = (byte)mid;
bytes[5] = (byte)(mid >> 8);
bytes[6] = (byte)(mid >> 0x10);
bytes[7] = (byte)(mid >> 0x18);
bytes[8] = (byte)hi;
bytes[9] = (byte)(hi >> 8);
bytes[10] = (byte)(hi >> 0x10);
bytes[11] = (byte)(hi >> 0x18);
bytes[12] = (byte)flags;
bytes[13] = (byte)(flags >> 8);
bytes[14] = (byte)(flags >> 0x10);
bytes[15] = (byte)(flags >> 0x18);
return bytes;
}
The .NET library implemented Decimal.GetBytes()
method internally.
I've used the decompiled .NET library to create a simple conversion methods between decimal and byte arrary - you can find it here:
https://gist.github.com/eranbetzalel/5384006#file-decimalbytesconvertor-cs
EDIT : Here is the full source code from my link.
public decimal BytesToDecimal(byte[] buffer, int offset = 0)
{
var decimalBits = new int[4];
decimalBits[0] = buffer[offset + 0] | (buffer[offset + 1] << 8) | (buffer[offset + 2] << 16) | (buffer[offset + 3] << 24);
decimalBits[1] = buffer[offset + 4] | (buffer[offset + 5] << 8) | (buffer[offset + 6] << 16) | (buffer[offset + 7] << 24);
decimalBits[2] = buffer[offset + 8] | (buffer[offset + 9] << 8) | (buffer[offset + 10] << 16) | (buffer[offset + 11] << 24);
decimalBits[3] = buffer[offset + 12] | (buffer[offset + 13] << 8) | (buffer[offset + 14] << 16) | (buffer[offset + 15] << 24);
return new Decimal(decimalBits);
}
public byte[] DecimalToBytes(decimal number)
{
var decimalBuffer = new byte[16];
var decimalBits = Decimal.GetBits(number);
var lo = decimalBits.Value[0];
var mid = decimalBits.Value[1];
var hi = decimalBits.Value[2];
var flags = decimalBits.Value[3];
decimalBuffer[0] = (byte)lo;
decimalBuffer[1] = (byte)(lo >> 8);
decimalBuffer[2] = (byte)(lo >> 16);
decimalBuffer[3] = (byte)(lo >> 24);
decimalBuffer[4] = (byte)mid;
decimalBuffer[5] = (byte)(mid >> 8);
decimalBuffer[6] = (byte)(mid >> 16);
decimalBuffer[7] = (byte)(mid >> 24);
decimalBuffer[8] = (byte)hi;
decimalBuffer[9] = (byte)(hi >> 8);
decimalBuffer[10] = (byte)(hi >> 16);
decimalBuffer[11] = (byte)(hi >> 24);
decimalBuffer[12] = (byte)flags;
decimalBuffer[13] = (byte)(flags >> 8);
decimalBuffer[14] = (byte)(flags >> 16);
decimalBuffer[15] = (byte)(flags >> 24);
return decimalBuffer;
}
As others have mentioned, use the BitConverter
class, see the example below:
byte[] bytez = new byte[] { 0x00, 0x00, 0x80, 0x3F };
float flt = BitConverter.ToSingle(bytez, 0); // 1.0
bytez = new byte[] { 0x00, 0x00, 0x00, 0x40 };
flt = BitConverter.ToSingle(bytez, 0); // 2.0
bytez = new byte[] { 0, 0, 192, 190 };
flt = BitConverter.ToSingle(bytez, 0); // -0.375
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