Issue: Bounday values that breaks VM

[karlosmid]

Hi!
We have found following issue:

d = Decimal.new("1E-924963747")
Decimal.to_float(d)

This kills VM (after some time)

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    (decimal 2.1.1) lib/decimal.ex:1696: Decimal.pow10/1
    (decimal 2.1.1) lib/decimal.ex:1696: Decimal.pow10/1
    (decimal 2.1.1) lib/decimal.ex:1687: Decimal.ratio/2
    (decimal 2.1.1) lib/decimal.ex:1501: Decimal.to_float/1
    iex:5: (file)

With

Erlang/OTP 26 [erts-14.1.1] [source] [64-bit] [smp:12:12] [ds:12:12:10] [async-threads:1] [jit]

Interactive Elixir (1.15.6) - press Ctrl+C to exit (type h() ENTER for help)

[ericmj]

On my machine it doesn't kill the VM, but I do get a SystemLimitError exception after a while.

In the ratio/2 implementation https://github.com/ericmj/decimal/blob/v2.1.1/lib/decimal.ex#L1686-L1687, or as a pre-check, we are missing checks for DBL_MIN and DBL_MAX as described here https://www.exploringbinary.com/correct-decimal-to-floating-point-using-big-integers/. There is no point in trying to create a larger or smaller float as they cannot be represented.

[karlosmid]

Hi, thank you for explanation. Our problem is that we get through protobuf this extra small integer. And in concurrent env, at the end we get out of memory for to_float calculation.
We will implement on our side DBL_MIN and DBL_MAX checks.
If you would like, I can do for Decimal this PR request.
Thanks again for creating this awesome library!

[ericmj]

Yes, any contributions would be very welcome. Thank you!

[wojtekmach]

Fixed in #207.