Now I'm nearly glad to have sent this "illegal" code to list, because this discussion was very interesting to me. But as Michael said, if you put "#include <stdio.h>" above it and turn "int" to "unsigned int" you will have nice deterministic C code and it does still miscompile. FYI, the code is developed from a orginal MD4 hash routine of the Samba 3 suite that miscompiles on my machine and during making it little and easy to see whether there is a compiler bug or not lazyness made me use "int" from the original "uint32" type. But the compilers of all people tested it with "int" seem to take the same path through "undefined chaos" even with O2 :-) Thanks to all Daniel -----Ursprüngliche Nachricht----- Von: Robert Dewar [mailto:dewar@xxxxxxxx] Gesendet: Mittwoch, 17. November 2004 14:07 An: Steven Bosscher Cc: Luca Benini; Dave Korn; 'Gerald Pfeifer'; 'Beschorner Daniel'; gcc@xxxxxxxxxxx; gcc-help@xxxxxxxxxxx Betreff: Re: gcc 3.3 / i386 / -O2 question Steven Bosscher wrote: > Hah, but there you are. Define "non-altering-semantic-option" > for something that according to the standard does not *have* > semantics. Reminds me of a famous exchange in the discussion of Algol-68 semantics at one meeting. Someone asked Charles Lindsay what undefined meant. He replied that it could mean anything, up to and including "unimaginable chaos". Geerhardt Goos then enquired (in a rather emphatic manner) "But how can I implement unimaginable chaos in my compiler?") :-) One interesting paragraph in the Algol-68 report specifies that at any point in the execution of the program, further elaboration of the program can be "interrupted", and that if such an interrupt occurs, further semantics are undefined. Sounds a bit drastic, until you learn that the paragraph derived from a discussion of what the situation was if an earthquake occurred during the execution of a program, causing the computer to be destroyed. Operating in a formal mode, the committee decided that they could not have a specification that would require conforming compilers to ensure against the possibility of earthquakes :-)
