of_string for unsigned integers does not raise exception on negative inputs

[anton-trunov]

Actual behavior

Here is a toplevel session:

μ> #require "stdint";;
μ> "-1" |> Stdint.Uint128.of_string |> Stdint.Uint128.to_string;;
- : string = "340282366920938463463374607431768211455"

Basically, this is the maximum 128-bit unsigned integer. It behaves the same for the rest of bit widths.

Expected behavior

Raises an exception according to the description here:

ocaml-stdint/lib/stdint.mli

Lines 292 to 297 in 48f97cd

	(** Convert the given string to an integer of type [t].
	The string is read in decimal (by default) or in hexadecimal, octal
	or binary if the string begins with [0x], [0o] or [0b] respectively.
	Raise [Failure "*_of_string"] if the given string is not a valid
	representation of an integer, or if the integer represented exceeds
	the range of integers representable in type [t]. *)

:

[rgrinberg]

Yes, that seems confusing. @rixed what do you think?

[rixed]

Given the quoted documentation and the fact that other Int modules seem to raise an exception (although not Failure but Invalid_arg, which looks better to me), I'd say that Uint128.of_string should indeed raise.
I would favor if all of the of_string functions would raise the same exception BTW.