ken@aiai.ed.ac.uk (Ken Johnson) (09/11/89)
In article <575@calmasd.Prime.COM> wlp@calmasd.Prime.COM (Walter Peterson) writes: >C has bitwise operators for AND (&), OR (|) and XOR (^) and boolean >operator for AND (&&) and OR (||), but not for XOR (^^). [...] Why >make people go to the trouble of writing something like >(a || b) && (!(a && b)) when a ^^ b is so much "cleaner". I can't tell you why ^^ isn't in the language, but note that A^^B would probably have a property that the above longer expression does not have, namely: A && B and A || B each evaluate the second argument only if necessary, and at most once. In some cases, evaluating A ^^ B by your suggested method would require evaluating A or B more than once. So a more suitable expression might be int X1, Y1; if ((X1 = A) && (!(X2 = B))) || (X2 && !X1) {...} Or you could just use goto's -- I think they would be justified here if you explain what they do. -- Ken Johnson, AI Applications Institute, 80 South Bridge, Edinburgh EH1 1HN E-mail ken@aiai.ed.ac.uk, phone 031-225 4464 extension 212 `I have read your article, Mr. Johnson, and I am no wiser than when I started.' -- `Possibly not, sir, but far better informed.'
bazza@hppad.HP.COM (Carlos Bazzarella) (09/13/89)
/ hppad:comp.lang.c / wlp@calmasd.Prime.COM (Walter Peterson) / 5:52 pm Sep 10, 1989 / Perhaps someone can answer a question that has bugged me since I first learned C almost 10 years ago. C has bitwise operators for AND (&), OR (|) and XOR (^) and boolean operator for AND (&&) and OR (||), but not for XOR (^^). Why? What happened to the boolean XOR operator ? If && makes sense for the boolean AND and || makes sense for the boolean OR, why doesn't ^^ make sense for the boolean XOR ? Most assemblers that I know have XOR as a single instruction so why make people go to the trouble of writing something like (a || b) && (!(a && b)) when a ^^ b is so much "cleaner". Can anyone tell me why this was left out of the language ? Is there any chance that some future version of ANSI-C will have it ? -- Walt Peterson. Prime - San Diego R&D (Object and Data Management Group) "The opinions expressed here are my own." ----------
bazza@hppad.HP.COM (Carlos Bazzarella) (09/13/89)
Ops!! response 3 was caused by accident
when I was reading the note. I didn't
know how to recover from the mistake.
I am sorry for the inconvinience.
Carlos Bazzarella.