XCAS float precision

[Albert Chan]

(10-04-2018 07:22 PM)parisse Wrote:  Xcas is using longfloats (via MPFR) for representation of floats having more than 14 digits.

Thanks you. It now make sense.

pibf := 3.141592653589793 // bigfloat
pi53 := 3.141592653 + 5.89793-10 // machine float

evalf(pibf, 20) => 3.1415926535897928940 // big float confirmed
evalf(pi53, 20) => 3.14159265359 // pi53 is 0.5 ULP bigger than pibf

It seems when big float mixed with machine float, big-float is "demoted".

evalf(pibf + 0.0, 20) => 3.14159265359
pibf - pi53 //==> 0.0

pibf == pi53 //==> true, big float demoted before comparison.