[meta] failed asserts in int128.nim

[narimiran]

This is a meta-issue, which tries to collect all the issues that are open because some assert in int128.nim has failed. The idea is to have all of them in once place, because one fix might potentially close multiple issues.

1. int128.nim(68, 11) `arg.sdata(3) == -1` out of range [AssertionDefect]

   • ---> for both issues, the value of args.sdata(3) is low(int32) (-2147483648)
   • [ ] https://github.com/nim-lang/Nim/issues/8868
   • [ ] https://github.com/nim-lang/Nim/issues/9326

2. int128.nim(71, 11) `arg.sdata(3) == 0` out of range [AssertionDefect]

   • [x] https://github.com/nim-lang/Nim/issues/12684

3. int128.nim(72, 11) `arg.sdata(2) == 0` out of range [AssertionDefect]

   • ---> for all issues, the value of args.sdata(2) is 1
   • [x] https://github.com/nim-lang/Nim/issues/6834
   • [ ] https://github.com/nim-lang/Nim/issues/8141
   • [ ] https://github.com/nim-lang/Nim/issues/12938
   • [ ] https://github.com/nim-lang/Nim/issues/14193
   • [ ] https://github.com/nim-lang/Nim/issues/17974

4. int128.nim(330, 11) `false` overflow [AssertionDefect]

   • [x] https://github.com/nim-lang/Nim/issues/12636
   • [x] https://github.com/nim-lang/Nim/issues/12897

First three points (lines 68, 71, 72) are part of proc toInt64*(arg: Int128): int64. The last point (line 330) is part of proc `*`(a: Int128, b: uint32): Int128.

[krux02]

I looked into this because I thought there would be a bug in int128. But these are all overflow and out of range error messages. The error messages could be improved for sure, but here is no bug in int128.