danielmarjamaki added inline comments. ================ Comment at: clang-tidy/misc/LongCastCheck.cpp:97 @@ +96,3 @@ + + if (!CastType->isIntegerType() || !SubType->isIntegerType()) + return; ---------------- LegalizeAdulthood wrote: > danielmarjamaki wrote: > > LegalizeAdulthood wrote: > > > Why don't you check for casting a `float` expression to a `double` or > > > `long double`? > > > > > > Isn't this the exact same issue? > > > > > > If so, add a test case for casting a `float` expression to `double` and a > > > test case for casting a `double` expression to a `long double`. > > in theory yes.. but somehow that feels strange to me. yes there will > > possibly be loss of precision in some decimals, that is normal when using > > floating point numbers. if such loss of precision would be unwanted then > > float should be avoided to start with. > > > > so I do agree in theory but I don't think I would feel good about adding > > such warnings. > > > For floating-point quantities, when I think of the term "precision" I am > thinking of the number of bits allocated to the mantissa. This may or may > not be correct terminology according to floating-point experts, but from what > I can tell it seems to agree with how the term is used on wikipedias [[ > https://en.wikipedia.org/wiki/Floating_point | article on floating-point ]]. > > So while digits are technically lost when we add a small floating-point > quantity to a large floating-point quantity (the large quantity gobbles up > all the bits of the mantissa and the small quantity has its least-significant > mantissa bits discarded), the precision of the result isn't changed -- the > number of bits in the mantissa is the same for the result as it was for the > inputs. > > To then take a quantity of N bits of mantissa and cast that to a quantity of > M bits of mantissa where M > N seems just as pointless as the approach of > casting an `int` to a `long`. The extra tokens for casting do absolutely > nothing and are redundant as far as the computation as written is concerned. It does feel strange to me. But I think you are technically right. I can implement it and see what warnings that generates.
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