[metapost] Accuracy of numbersystem double

[Daniel H. Luecking]

I would like to know a few details of numbersystem double.

(1) I assume a double is stored in binary format with some fixed 
number of significant binary places. If not, I'd be pleased to 
know that.

(2) If so, how many binary places? It seems 52, but I'd like to know for sure.

Also, I can understand why   show X;  might round to 15 decimal 
places, but it seems to me that there should be some way to display 
a value with full accuracy.   decimal X  does not produce that.  In fact  
X = scantokens decimal X  is false for the assignment 
X := 3.1415926535897934;  in MetaPost 1.803 (TeX Live 2013/W32TeX). 
This reduces its usefulness in debugging. 

(3) So: is there a way to display accurate values of variables in 
numbersystem double?

Regards,
Dan

Daniel H. Luecking
Department of Mathematical Sciences
University of Arkansas
Fayetteville, Arkansas