Is it worth it to implement it in hardware? If yes why? If not why not?
Sorry I thought it is clear that I am talking about Decimal Rational Numbers! Ok something like decNumber++ for C++, decimal for .NET... Hope it is clear now :)
Why aren't Floating-Point Decimal numbers hardware accelerated like Floating-Point Binary numbers?
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Some IBM processors have dedicated decimal hardware included (Decimal Floating Point | DFP- unit).
In contribution of answered Sep 18 at 23:43 Daniel Pryden
the main reason is that DFP-units need more transistors in a chip then BFP-units. The reason is the BCD Code to calculate decimal numbers in a binary environment. The IEEE754-2008 has several methods to minimize the overload. It seems that the DPD hxxp://en.wikipedia.org/wiki/Densely_packed_decimal method is more effective in comparison to the BID hxxp://en.wikipedia.org/wiki/Binary_Integer_Decimal method.
Normally, you need 4 bits to cover the decimal range from 0 to 9. Bit the 10 to 15 are invalid but still possible with BCD. Therefore, the DPD compress 3*4=12 bit into 10 bit to cover the range from 000 to 999 with 1024 (10^2)possibilities.
In general it is to say, that BFP is faster then DFP. And BFP need less space on a chip then DFP.
The question why IBM implemented a DFP unit is quite simple answered: They build servers for the finance market. If data represents money, it should be reliable.
With hardware accelerated decimal arithmetic, some errors do not accour as in binary. 1/5 = 0.2 => 0.0110011001100110011001100110... in binary so recurrent fractions could be avoided.
And the overhelming round() function in excel would be useless anymore :D (->function =1*(0,5-0,4-0,1) wtf!)
hope that explain your question a little!
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