I'd like to be able to get the bits from a System.Decimal value and then convert that to the string representation of the value, much like Decimal.ToString() would do but I have a hard time coming up with the algorithm.
So I have something like this:
decimal d = 1403.45433M;
int[] nDecimalBits = decimal.GetBits(d);
// How to convert the 4 integers in nDecimalBits to a string
// that contains "1403.45433"?
I know the binary layout of the decimal - the first 3 integers contain the value bits and the last integer contains the sign bit and the scaling factor.
I tried searching for the algorithm using various search terms but decimal is mostly used as a synonym for 'floating-point number' so my searches turned up answers to unrelated problems.
Any help would be appreciated.
Edit: in response to some answers, I need to send the bits to a different platform where the value needs to be reconstructed. System.Decimal and any of its member functions are not available there, so I need to grab the bits and translate them to a string.
If I had a choice, I'd obviously use ToString() but then I wouldn't need to ask.
Since you cannot use ToString(), you might want to check out how the mono developers implemented this:
- https://github.com/mono/mono/blob/master/mcs/class/corlib/System/NumberFormatter.cs
The entry point is NumberToString(string, decimal, IFormatProvider).
The interesting part is InitDecHexDigits(uint, ulong), which gets called like this
InitDecHexDigits ((uint)bits [2], ((ulong)bits [1] << 32) | (uint)bits [0]);
and does the "bit juggling and shifting" thing to convert the three integers into binary coded decimals (_val1 to _val4), which can then be (trivially) converted into a string.
(Don't get confused by the fact that they call it "hex representation". It's binary coded decimal digits.)
You can use the Decimal constructor Decimal(Int32[]) to convert your value back:
Decimal Constructor (Int32[])
Initializes a new instance of Decimal to a decimal value represented in binary and contained in a specified array.
Afterwards, you can use ToString if you want.
Example:
decimal d = 1403.45433M;
int[] nDecimalBits = decimal.GetBits(d);
decimal d2 = new decimal(nDecimalBits);
string s = d2.ToString();
It's does not algoritm, but i suppose it should help.
Decimal bits structure:
The binary representation of a Decimal
number consists of a 1-bit sign, a
96-bit integer number, and a scaling
factor used to divide the integer
number and specify what portion of it
is a decimal fraction. The scaling
factor is implicitly the number 10,
raised to an exponent ranging from 0
to 28.
The return value is a four-element
array of 32-bit signed integers.
The first, second, and third elements
of the returned array contain the low,
middle, and high 32 bits of the 96-bit
integer number.
The fourth element of the returned
array contains the scale factor and
sign. It consists of the following
parts:
Bits 0 to 15, the lower word, are
unused and must be zero.
Bits 16 to 23 must contain an exponent
between 0 and 28, which indicates the
power of 10 to divide the integer
number.
Bits 24 to 30 are unused and must be
zero.
Bit 31 contains the sign; 0 meaning
positive, and 1 meaning negative.
Is there any major reason you can't just use the decimal constructor?
new decimal(nDecimalBits).ToString();
