Hi Tianyou, I am not enough of a physicist to know what “the qualification of the ground state energy in a quantum system” means, but this does not sound like a Clang bug to me. You did not say whether `a` in your example is a float or a double, but the minimum legal values for these types are the constants FLT_MIN and DBL_MIN. There is no need to try to compute them. Exceeding the range of values representable in a type — [FLT_MIN, FLT_MAX] or [DBL_MIN, DBL_MAX] — is undefined behavior, so the compiler is free to emit anything.
Thanks, Matt > On May 26, 2020, at 20:31, Tianyou via cfe-users <cfe-users@lists.llvm.org> > wrote: > > Hello everyone, > I found some questionable behaviors in the clang compiler. > I tried to calculate the smallest number in my machine with clang. I did it > by looping as: > a = a / 1.73 > In g++, after 1358 loops, I found that a = 4.94066E-324, and the value of a > never changes from loop 1358 till the end 1500 loop. > It is questionable for me that a non zero real number here a = 4.94066E-324 > divided by a non zero and non one real number here 1.73 will keep the same > value. The phenomenon seems to the qualification of the ground state energy > in a quantum system. > Is this bug for the clang compiler? > I tested my code with, g++ (Apple LLVM version 10.0.0, clang-1000.10.44.4) on > Macintosh. I also tried a = a / 1.7, a = a / 1.77. > All have similar results. A ground state qualification and unchanged value of > a. > I guess that it is related to the binary system used by the computer system. > Here with my codes. > > Best wishes > Tianyou Yi > Postdoc researcher in National Tsing Hua University > > Best wishes > Tianyou Yi > Please send me to > yitianyo...@qq.com > yitianyou9...@gzemail.cn > > > > _______________________________________________ > cfe-users mailing list > cfe-users@lists.llvm.org > https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
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