On Sunday, July 13, 2003, at 1:11PM, M. Warner Losh wrote: > In message: <20030713152154.GA96653_at_stack.nl> > Jilles Tjoelker <jilles_at_stack.nl> writes: > : The compiler moans about (T)(-1) >= 0 as well. Is the assumption that > : (unsigned type)(-1) is never zero valid? > > yes. There are no known machines where -1 == 0 for types of different > signs. Further, the C standard says that it must behave as if it is a > two's complement machine, and I think that C++ says so too. > I am pretty certain you can do one's compliment in the C99 standard, and that some of that is implementation/platform dependant. See section 6.2.6.2 of the C99 standard which enumerates the following 3 negative number representations: ¡Xthe corresponding value with sign bit 0 is negated (sign and magnitude); ¡Xthe sign bit has the value-(2^N )(two¡¦s complement); ¡Xthe sign bit has the value-(2^N -1) (one¡¦s complement). further: "Which of these applies is implementation-defined, as is whether the value with sign bit 1 and all value bits zero (for the first two), or with sign bit and all value bits 1 (for one¡¦s complement), is a trap representation or a normal value. Inthe case of sign and magnitude and one¡¦scomplement, if this representation is a normal value it is called a negative zero. " Yes... a negative 0. > Warner > _______________________________________________ > freebsd-current_at_freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to > "freebsd-current-unsubscribe_at_freebsd.org"Received on Sun Jul 13 2003 - 09:25:58 UTC
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