Python fails on math

Robert Kern robert.kern at
Thu Feb 24 11:40:45 EST 2011

On 2/24/11 5:55 AM, Steven D'Aprano wrote:
> On Wed, 23 Feb 2011 13:26:05 -0800, John Nagle wrote:
>> The IEEE 754 compliant FPU on most machines today, though, has an 80-bit
>> internal representation.  If you do a sequence of operations that retain
>> all the intermediate results in the FPU registers, you get 16 more bits
>> of precision than if you store after each operation.
> That's a big if though. Which languages support such a thing? C doubles
> are 64 bit, same as Python.

C double *variables* are, but as John suggests, C compilers are allowed (to my 
knowledge) to keep intermediate results of an expression in the larger-precision 
FPU registers. The final result does get shoved back into a 64-bit double when 
it is at last assigned back to a variable or passed to a function that takes a 

Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco

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