Formatting BigDecimal loses precision

[JayXon]

require"big"
pi="3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067982148086513282306647093844609550582231725359408128481117450284102701938521105559644622948954930381964428810975665933446128475648233786783165271201909145648566923460348610454326648213393607260249141273724587".to_big_d
puts pi.round(100)
puts "%.100f"%pi

3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117068
3.1415926535897931159979634685441851615905761718750000000000000000000000000000000000000000000000000000

https://play.crystal-lang.org/#/r/hfg9

[JayXon]

BigFloat too

[HertzDevil]

GMP BigFloat is fundamentally limited, so we have to reimplement everything ourselves unless we switch to MPFR: #11410

BigDecimal should work.