https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87390
--- Comment #23 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> --- (In reply to jos...@codesourcery.com from comment #22) > 6.3.1.8 specifies *types*. It only gives some partial information about > *evaluation formats*, which is essentially a consequence of information > elsewhere (it states the possibility of wider evaluation formats, while > never requiring them to be used, and states that when they are used they > don't affect the types). No, this does not reflect the historical practice. Information in 6.3.1.8 predates information you can find elsewhere. You can see a C89 draft here: https://port70.net/~nsz/c/c89/c89-draft.html 3.2.1.5 Usual arithmetic conversions[*] (which was the old 6.3.1.8) already has: "The values of operands and of the results of expressions may be represented in greater precision and range than that required by the type; the types are not changed thereby." but information you can now find in 5.2.4.2.2 is not present (in particular, FLT_EVAL_METHOD does not exist). [*] https://port70.net/~nsz/c/c89/c89-draft.html#3.2.1.5 > I think 5.2.4.2.2 has the main specification of > when wider evaluation formats are used. It completes information from 6.3.1.8. But if FLT_EVAL_METHOD = -1, this is just like old C89 behavior and its clause 3.2.1.5 (corresponding to 6.3.1.8 in C99). > I think the combined effect of > 5.2.4.2.2 and 6.3.1.5 is that the particular form of implicit conversion > involved in the usual arithmetic conversions does not *remove* excess > range and precision from an operand to an operator that applies the usual > arithmetic conversions, but that this does not result in excess precision > being *introduced* by such an implicit conversion when the argument was of > integer type, in the absence of any explicit wording providing for such > conversions to result in a value with excess precision. 5.2.4.2.2p8 does not have specific rules for integer types. It says "[...] values subject to the usual arithmetic conversions [...] are evaluated to a format whose range and precision may be greater than required by the type." This is quite clear: values subject to the usual arithmetic conversions can either be floating-point values or integer values, as described in "6.3.1.8 Usual arithmetic conversions". And for FLT_EVAL_METHOD = 2, the format in question is long double.
