在 2018/9/22 18:08, Vincent Lefevre 写道: > Bug reported here: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87390 > (note that the tests do not involve constants, these are just about > implicit type conversions). > That's about contraction. The behavior in the OP can only be observed when no optimization is enabled (i.e. with `-O0`) or when strict standard compliance is requested (i.e. with `-std=c99` or `-ansi`) and no `-ffp-contract=fast` is in effect. It is irrelevant to this issue. Contraction is about what happens within a floating-point operation, but in your program (the standard says) `2147483647` is converted to type `float` before the floating-point comparison, so it behaves as if you had added a cast like `f == (float)2147483647`. This implicit conversion can be observed by compiling the program in question with `-Wconversion`. You already had precision loss BEFORE the comparison which is irrecoverable by any evaluation method. -- Best regards, LH_Mouse
