modulus redux

[Andrei Alexandrescu]

Walter Bright wrote:
> Andrei Alexandrescu wrote:
>> Don wrote:
>>> Close, but that's technically not true in the case where abs(a/b) > 
>>> long.max. (The integer doesn't have to fit into a 'long').
>>
>> But if real is 79-bit long (as on Intel), the largest integer that 
>> could fit without loss in 1 << 63, and that would fit in a long. Are 
>> you saying r could spill into large integers that cannot be 
>> represented without loss?
> 
> The definition is without regard to the size of integral types. It only 
> means "integer".
> 
> 
>>> In IEEE754, r= a % b is defined by the mathematical relation r = a  – 
>>> b  * n , where n is the integer nearest the exact number a/b ; 
>>> whenever abs( n  – a/b) = 0.5 , then n is even. If r == 0 , its sign 
>>> is the same as a.
>>
>> I take it D does not define a % b the IEEE 754 way (that's why I 
>> eliminated that mention). Is that correct?
> 
> No, it is defined as fmod, which is IEEE754 %. In fact, it is quite 
> literally implemented by the FPREM instruction which is the same used 
> for fmod().
> 
> Hmm, I just noticed that the code generator should use FPREM1 instead to 
> get IEEE conformance. Darn.
> 
> http://www.sesp.cse.clrc.ac.uk/html/SoftwareTools/vtune/users_guide/mergedProjects/analyzer_ec/mergedProjects/reference_olh/mergedProjects/instructions/instruct32_hh/vc108.htm 
> 
> 
> http://www.sesp.cse.clrc.ac.uk/html/SoftwareTools/vtune/users_guide/mergedProjects/analyzer_ec/mergedProjects/reference_olh/mergedProjects/instructions/instruct32_hh/vc109.htm 
> 

http://d.puremagic.com/issues/show_bug.cgi?id=3171

What are friends for?


Andrei