[Cython] constant folding for floats?

[Robert Bradshaw]

On Apr 6, 2009, at 10:38 AM, Stefan Behnel wrote:

> Carl Witty wrote:
>> On Mon, Apr 6, 2009 at 10:15 AM, Stefan Behnel wrote:
>>> should we enable constant folding for floats by using the decimal  
>>> module?
>>
>> I don't think so.
>>
>> 1) Is there any advantage to doing constant folding in Cython instead
>> of letting the C compiler do it?
>
> Well, yes. In many situations, Cython can use values that are known at
> compile time to generate simpler code, e.g. avoid Python type  
> conversions
> or move code sections into C completely. Loops are a great example.  
> Cython
> 0.12 will bring another couple of enhancements here.
>
> Not sure if this really applies to float values, so we might end up
> postponing this discussion until there is a concrete reason to  
> enable this.
>
>
>> 2) If I write a constant floating-point expression, I expect it to be
>> evaluated according to IEEE rounding rules.  (So I would prefer doing
>> the constant folding using Python floats, which will usually match  
>> the
>> computations performed in the target, rather than the decimal module,
>> which won't match the target.)
>
> Makes sense to me.

+1 Using the decimals module here seems strange. Note that one needs  
to use repr rather than str to get enough digits to accurately  
represent constants in the source.

- Robert