truncate/1 incorrect

[UWN]

?- X is truncate(1.0e300).
   X = 9223372036854775807, unexpected. % should be much much larger
?- X is 1.0*truncate(1.0e300).
   X = 9.223372036854776e18, unexpected.
   X = 1.0e300. % expected, but not found

[UWN]

In fact,

?- between(1,400,N),F is 10**N,V is truncate(F), V = 9223372036854775807.
   N = 19, F = 1.0e19, V = 9223372036854775807, unexpected
;  ...
;  N = 308, F = 1.0e308, V = 9223372036854775807, unexpected
;  error(evaluation_error(float_overflow),(**)/2).
   evaluation_error(float_overflow). % expected, but not found directly

[UWN]

?- 0x7fffffffffffffff = 9223372036854775807.
   true.

[triska]

From a preliminary glance, I found:

scryer-prolog/src/machine/dispatch.rs

Line 938 in 00e6e32

self.machine_st.interms[t - 1] = truncate(n1, &mut self.machine_st.arena);

But the function that may yield a more correct result (if rounded) seems to be trunc (not truncate) (dubious!). @bakaq, @adri326, I would greatly appreciate your input and help with this, thank you a lot!

[adri326]

Oh this is the place I couldn't find again while working on this part of the codebase. rnd_i casts f (an f64) into an i64 and then into an Integer. The fix would be to use Integer::try_from(f) instead

[adri326]

Yup, that does the trick :)