Double implicitly converted to real

[bearophile]

Charles McAnany Wrote:

> I noticed that one of the guarantees in TDPL is that any code that is valid in both C
> and D should compile with the same result.

This is almost true (there are few differences, in D fixed-size arrays are managed by value instead of by pointer, and global floating point variables are initialized to NaN instead of 0), but only where all C compilers themselves give the same results.

Floating point operations are based on a standard implementation, but I think in practice different optimizations cause different C compilers to not give exactly the same result when floating point values are used (even the same CPU gives different results if you use the FP stack with 80 bit reals or if you use 64 bit doubles in SSE registers). So small differences are expected. Your program is designed to blow up those small differences.


> It seems D is implicitly converting double to real. Is this the usual behavior?

DMD compiler sometimes uses real values for intermediate values, so such differences are not so unexpected.

Bye,
bearophile