Cannot find the sqrt of a BigDecimal with unlimited precision

[ryan-williams]

import spire.algebra._, spire.implicits._
Field[BigDecimal].fromDouble(0).sqrt

throws:

java.lang.ArithmeticException: Cannot find the sqrt of a BigDecimal with unlimited precision.
  at spire.std.BigDecimalIsNRoot.sqrt(bigDecimal.scala:43)
  at spire.std.BigDecimalIsNRoot.sqrt$(bigDecimal.scala:41)
  at spire.std.BigDecimalAlgebra.sqrt(bigDecimal.scala:177)
  ... 36 elided

Affects 0.13.0 and (org.typelevel) 0.14.1

BigDecimalIsField.fromDouble returns a BigDecimal with UNLIMITED precision; I don't have context to know if that is unconditionally a bug or not.

[ryan-williams]

NB: changing UNLIMITED to DECIMAL64 in BigDecimalIsField.fromDouble results in FpFilterTest Orientation test for degenerate case failing, though it seems like that test may not really be verifying anything useful.

[denisrosset]

@non, is it related to the stuff that you fixed yesterday?

[kschwarz1116]

Not super familiar with how precision is supposed to work, but this doesn't seem like it's an issue yet. (And arguably, it seems like the behavior makes sense). Might make sense to close.