[metapost] Accuracy of numbersystem double
taco at elvenkind.com
Tue Feb 11 10:00:00 CET 2014
On 10 Feb 2014, at 22:21, Daniel H. Luecking <luecking at uark.edu> wrote:
> 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.
The numbersystem ‘double’ is a standard C language ‘double’. On
all modern systems that should translate to EEE 754 double-precision
binary floating-point format binary64.
> (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?
It would be quite straightforward to change ‘decimal’ so that it matches
the input reader ?
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