FractionApprox rejects inputs above 0x7FFFFFFF because they cannot be stored
as a fraction, but the check was one-sided while the sign is stripped right
after it. A large negative value therefore reached the continued-fraction loop
and overflowed the terms it accumulates. ICSharpCode.Decompiler is built with
CheckForOverflowUnderflow, so that aborted decompilation of the whole member
instead of wrapping.
Found by fuzzing nuget.org; reproduces on MathNet.Numerics, whose constants
reach the approximation through their ratio to PI.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
Siegfried Pammer