Jeff Muizelaar [:jrmuizel] Reporter
	Description • 15 years ago

qcms has a bunch of code like:

float p;
...
p *= 65535.;

Since the type of 65535. is a double this code will promote p to a double to do the multiply. This causes the, likely unintended, conversion to double and conversion back to float.

It would be nice if we could warn about situations like this.

	Prarthana
	Comment 1 • 15 years ago

I am a student from SJCE, Mysore India and would like to take up this bug.

	Nathan Froyd [:froydnj]
	Comment 2 • 13 years ago

FWIW, GCC >= 4.6 already has an option to do this (-Wdouble-promotion).  The implementation was straightforward; I don't think it would be too hard to port it to clang, if it's not already there.

	(dormant account)
	Comment 3 • 13 years ago

Sounds like a good minor reason to bump gcc...if anyone feels bored :)

	Chris Peterson [:cpeterson]
	Comment 4 • 6 years ago

clang also supports the -Wdouble-promotion warning:

> warning: implicit conversion increases floating-point precision: A to B

https://clang.llvm.org/docs/DiagnosticsReference.html#wdouble-promotion

	Chris Peterson [:cpeterson]
	Comment 5 • 6 years ago

P5 because this warning is very noisy and, AFAIU, is a performance problem, not a correctness bug.

	Sylvestre Ledru [:Sylvestre]
	Comment 6 • 6 years ago

I don't think we will ever fix that, closing.