std.math performance (SSE vs. real)

[Walter Bright via Digitalmars-d]

On 6/29/2014 9:54 AM, Andrei Alexandrescu wrote:
> On 6/29/14, 8:50 AM, Iain Buclaw via Digitalmars-d wrote:
>> On 29 June 2014 15:59, Andrei Alexandrescu via Digitalmars-d
>> <digitalmars-d at puremagic.com> wrote:
>>> On 6/28/14, 9:36 PM, H. S. Teoh via Digitalmars-d wrote:
>>>>
>>>> On Sat, Jun 28, 2014 at 05:16:53PM -0700, Walter Bright via Digitalmars-d
>>>> wrote:
>>>>>
>>>>> On 6/28/2014 3:57 AM, Russel Winder via Digitalmars-d wrote:
>>>>
>>>> [...]
>>>>
>>>>>> Or indeed when calculating anything to do with money.
>>>>>
>>>>>
>>>>> You're better off using 64 bit longs counting cents to represent money
>>>>> than using floating point. But yeah, counting money has its own
>>>>> special problems.
>>>>
>>>>
>>>> For counting money, I heard that the recommendation is to use
>>>> fixed-point arithmetic (i.e. integer values in cents).
>>>
>>>
>>> A friend who works at a hedge fund (after making the rounds to the NYC large
>>> financial companies) told me that's a myth. Any nontrivial calculation
>>> involving money (interest, fixed income, derivatives, ...) needs floating
>>> point. He never needed more than double.
>>>
>>> Andrei
>>>
>>
>> I would have thought money would use fixed point decimal floats.
>
> And what meaningful computation can you do with such? Using fixed point for
> money would be like the guy in Walter's story rounding to two decimals after
> each step in the calculation.
>
> Even for a matter as simple as average price for a share bought in multiple
> batches you need floating point.

I can see using floating point for the calculation, but the final result should 
be stored as whole pennies.