How Can We Achieve Deterministic Floating-Point Results in .NET?

Coercing Floating-Point Calculations for Deterministic Results in .NET

Driven by the pursuit of consistent results across machines in .NET, developers grapple with the challenge of floating-point determinism. Without built-in solutions like Java's fpstrict, the issue appears to be insurmountable. While some have resorted to cumbersome fixed-point math, others have explored the potential of explicit casting.

As suggested by CLR engineer David Notario, inserting explicit casts after every floating-point operation may lead to predictable behavior. However, Eric Lippert cautions that the C# compiler merely gives a "hint" to the runtime to enable narrowing. It remains unclear whether this hint translates into the necessary IL conversions.

Delving into the C# specifications and the CLR specifications, we confirm that:

1. The C# compiler indeed inserts a conv.r4 opcode in the IL when an explicit cast to float is present in the source code.
2. The CLR spec mandates that a conv.r4 instruction truncates a value to its native size.

Despite this, explicit casting alone is insufficient to guarantee reproducibility across machines. The CLR potentially allows results to be stored in higher precision FPU registers during intermediate calculations. Assigning to a static field or array element can also force truncation.

Other factors, such as FPU settings, can still introduce variations. To ensure truly reproducible arithmetic, developers are advised to consider using integers instead.

The above is the detailed content of How Can We Achieve Deterministic Floating-Point Results in .NET?. For more information, please follow other related articles on the PHP Chinese website!