FatRat loss in precision from String

[rbt]

This occurs at the boundary of what a Rat can handle.

say '-0.1234567890123456774144'.FatRat;
#-0.123456789012345677   # Incorrect. Lost 4144

say '-0.123456789012345677414400000000000001'.FatRat;
# -0.123456789012345677414400000000000001   # Correct. Even larger value is maintained

Welcome to Rakudo™ v2022.07.
Implementing the Raku® Programming Language v6.d.
Built on MoarVM version 2022.07.

[colomon]

I think this is probably a precision issue in the output, rather than a problem with the actual stored FatRat.

'-0.1234567890123456774144'.FatRat.nude (-588687844335297 4768371582031250)

(switch to bc) scale=50 -588687844335297/4768371582031250 -.12345678901234567741440000000000000000000000000000

So it has the correct numerator and denominator internally, it's just not displaying all the digits when you output it.

--Sol

On Fri, Nov 25, 2022 at 3:51 PM rbt @.***> wrote:

This occurs at the boundary of what a Rat can handle.

say '-0.1234567890123456774144'.FatRat;

-0.123456789012345677 # Incorrect. Lost 4144

say '-0.123456789012345677414400000000000001'.FatRat;

-0.123456789012345677414400000000000001 # Correct. Even larger value is maintained

Welcome to Rakudo™ v2022.07.

Implementing the Raku® Programming Language v6.d.

Built on MoarVM version 2022.07.

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[2colours]

For the interested: this seems to be the method that produces the actual output: https://github.com/rakudo/rakudo/blob/63ead8d3d230010a6a5837be02437a202aea56b2/src/core.c/Rational.pm6#L112